At the moment, nobody knows for sure whether or not changes in the Sun's luminosity can cause long-term climate changes. There have been various studies done, most since the advent of global warming, that have tried to address this. The conclusions have been interesting:

The Sun is not responsible for the recent warming of the Earth.
It's not yet known whether or not the Sun has influenced climate in the past.

Here are some studies (one supporting each side of the long-term debate):

A report by the National Research Council (available here) found that sunspot activity could be a major contributor to small changes in the Sun's brightness. There is a periodic trend in sunspot activity that lasts 11 years, and studies have considered this when looking at long-term trends. One target of inquiry is the Maunder Minimum, a period of low sunspot activity:

The Maunder Minimum coincided with the Little Ice Age, a short period of low temperatures. In fact, the Sun may be entering a similar period within the next few decades. Observations could show whether or not there is a link between the two events.

However, the NRC concluded that it is hard, if not impossible, to find any data supporting theories that there is a long-term patter. Hal Maring summarized it best:

  Hal Maring, a climate scientist at NASA headquarters who has studied the report, notes that “lots of interesting possibilities were suggested by the panelists.  However, few, if any, have been quantified to the point that we can definitively assess their impact on climate.”

In the paper Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model by Holger et al., periods called Dansgaard–
Oeschger events were studied. These are climate oscillations lasting 1,470 years. Holger et al. analyzed ice cores from Greenland and attempted to model solar forcing, the amount of energy absorbed by Earth or radiated into space. They also used the ocean and atmosphere to account for changes (the NRC report, too, concluded that solar effects can trickle down through the atmosphere and other parts of Earth). Their conclusion was that, despite the fact that no records of 1,470-year solar cycle exist, the analysis supported a connection between solar variability and changes in Earth's climate.

Before anyone gets too excited, I'll add this: 1) I haven't been able to find any comments from other scientists on the paper, so I'm not sure how well-received it was, and 2) The 1,470-year cycle can not account for long-term glacial periods, or the recent rise in global temperatures.

Another potentially interesting (and paywalled) paper can be found here. An informative website is here, but I'm not sure if it's entirely neutral. It does seem to present both sides, though.

I'll end on this: Whether or not the Sun severely impacts the Earth's climate, Milankovitch cycles are the biggest influence on ice ages.

It will take some pretty drastic changes in the Sun's luminosity to change the glacial periods . . . which the Sun will be undergoing in about billion years or so. It will still be on the main sequence, and will stay there for 4.4 billion years more, but it will have brightened by about 10%.

Once of the consequences of this will be that the Earth will lose its oceans. Through a process called the "moist greenhouse" effect, water heats up and reaches the atmosphere, where the hydrogen atoms are freed from the oxygen atoms and escape to space. This occurs at a tiny, tiny rate at present, but in about one billion years, the Sun will be bright enough that this will occur at a catastrophic rate.

That places the last glacial period somewhere between now and one billion years in the future. To figure this out, we have to look at long term patterns, such as Milankovitch Cycles. This graph illustrates them best:

From the present day to the far right, though, is only 800,000 years. That's unhelpful. This graph, while a bit clearer, shows only the variations without accounting for any changes in the Sun's luminosity (though that will not affect us during the next 800,000 years!).

Here's the actual answer to your question: We don't know. That's because some parts of the Earth will be affected more by the Sun's brightening that others. For example, the NRC found that the Pacific Ocean experienced a strong relationship with solar activity. So as the Sun gets brighter, some areas could still be strongly affected by Milankovitch cycles, while others might find themselves getting hotter than they would normally be.

We can be sure of one thing, though: It will certainly be before one billion years from now!


Near-Surface Investigations: FWI vs. MASW

I think there are some initial exploratory abstracts out there on the topic, e.g., http://www.earthdoc.org/publication/publicationdetails/?publication=75396 . But not much yet.

My view is that that MASW (multichannel analysis of surface waves) is simply so much more robust in practice compared to FWI (full waveform inversion, which really doesn't work as spectacularly well as some papers may suggest; the method requires a LOT of iterative and hands-on work, and is furthermore extremely computationally demanding, without always giving dramatically better results compared to travel-time tomographies...)... hence, I think that MASW will remain the standard in the coming future, until FWI truly becomes a 'cheap' and 'hands-off' method, which could easily take another 15+ years, I imagine...


Regarding forest fire season and using robotic devices for proactive efforts before any fires

This is counterproductive, both ecologically and economically, and is also well beyond the capabilities of current robots.

Ecologically counterproductive
Forests have evolved to live with, and in many cases, to depend on forest fires. Aggressive fire prevention by the US Forest Service and other agencies throughout much of the 20th century resulted in unintended consequences. Many native species need fire to reproduce. For example, the pinecones of lodgepole pines remain sealed shut for years and only open when exposed to the high heat of a forest fire. Decades of active fire suppression led to the replacement of some of those native species by invasive ones.

Another unintended consequence was making large fires even larger. Some of the most intense fires happened in areas where small fires had been successfully suppressed for a number of years. The resultant buildup of dead wood, brush, and smaller trees gave fires a way to spread to the canopy level, something that didn't happen so often when small fires regularly burned away that lower level of fuel.

Economically counterproductive
One of the biggest fire threats to people is those people who insist on living in forested areas and then let the trees grow right next to their houses. The simplest solution: Don't do that then! The Forest Service and others offer education to homeowners on how to make their homes more fire resistant, and in some cases, polices areas to ensure homeowners are following some minimum standard.

Another solution, one not yet adopted by the Forest Service, is an approach taken by the Federal Emergency Management Agency with regard those who live in the most flood-prone areas. After flooding one too many times, FEMA essentially forces homeowners to sell their houses at market value to FEMA. FEMA then promptly tears them down and marks the area as uninsurable. This might appear to be a waste of money, but in the long run it saves FEMA money, and potentially saves lives. Texas and some other states take even more drastic measures with coastal properties. A house is condemned once the coast line has eroded to the point that it is closer than some minimal distance of the house.

We can't build such robots, yet
The terrain where forests grow is not exactly suitable to robots. Much of the forested land in the contiguous US is mountainous. What isn't mountainous is dotted with bogs, swamps, and lakes. The weather is often rather nasty. An autonomous robot that could navigate and survive through such terrain is far in the future. Adding the ability to clean up terrain is even further in the future.

Aggressive fire suppression requires clearing out shrubs such as chaparral, which is rather tough stuff, dead and down trees that can be several meters in diameter, and small to medium sized non-canopy trees whose trunk can be up to a meter or so in diameter. This is not the job for little goat-sized robots. This is a job for an industrial-sized robot, and ED-209 won't cut it.


What is the evidence it is feasible to reverse ocean acidification by adding large quantities of a base (bicarb soda)?

Instead of using sodium bicarbonate why not use limestone instead? Limestone is already used on an industrial scale to neutralise acids and acidic solutions. Also, sodium bicarbonate needs to be manufactured, whereas limestone just needs to be dug up. The manufacturing of sodium bicarbonate would unnecessarily use energy and potentially create more carbon dioxide if it were to be used to neutralise the worlds oceans.

Danny Harvey of the University of Toronto has already looked into this. His solution is to deposit 4 Gt/a of limestone into the oceans. To put this in perspective, global coal production in 2013 was nearly double this at 7.823 Gt and it is more than global iron ore production in 2014 of 3.22 Gt.

The mining of so much limestone would be a massive and expensive undertaking. Then there are the added costs of grinding the limestone to $40 \mu m$, as specified by Danny Harvey. Added to this would be the cost of depositing the finely ground limestone to the oceans. Because the limestone could not be expected to be dumped at one coastal location and then disperse globally, this would require a fleet of ships to deposit the limestone all over the oceans.

The other things to consider include:

Are there sufficient quantities of easily obtainable limestone to do
this?
What would such a use of limestone do to the supply and cost of
cement, used for construction, etc.?
What impact would such a huge annual deposition of limestone have of
ocean life forms and biodiversity?

The other thing that Danny Harvey states in his document is that 4 Gt of limestone would need to be deposited in the oceans annually for at least 200 years for "a modest additional benefit".


Could the Dead Sea dry up? and if so, when?

The Dead Sea salt is almost equally Mg-chloride and Na-chloride at about four times normal sea-salt salinity. This combination is extremely hygroscopic whilst, at this ultra low elevation and high temperature, there is very high humidity. People who try to towel themselves dry after swimming in the Dead Sea find that they can't - the salt absorbs atmospheric moisture as fast as they can towel it off. In addition to the chemical characteristics of the salt, at such high concentrations the water vapour pressure at the liquid surface is almost nothing. Therefore, it will require extreme and very prolonged dessiccation to dry out the Dead Sea completely. On the other hand the sea-level still has a long way to drop before it becomes a sort of slushy paste.


Why rely on climate models as opposed to paleoclimate data?

We need both paleodata and models, in fact the relationship between paleodata and the climate at a certain time is typically evaluated through models. Paleodata does not actually measure climate observables directly (tempreture/pressure/salinity/other) but instead is (e.g.) a geochemical quantity related to one of those.

For example, the two most frequently used records are the Antarctica EPICA ice core record and the Lisiecki Raymo benthic stack. The isotopes in these records are affected by temperature at a point on the planet and global ice volume, but how that relates to global temperature and the size of individual ice sheets requires inference from climate models.

Further, climate (or earth systems) models can allow us to probe what could happen in addition to what did happen. Current CO2 levels are reaching a point not seen in the ice core record (our most direct records) and so we need increasingly complex models to get a handle on the range of possibilities.


Does general relativity influence climate (vs Newtonian mechanics)

In short: No. Unless multi-million timescales are considered.

The reason we keep teaching Newtonian mechanics, is because it is a VERY accurate approximation of a more general theory (general relativity) within the regimes of speed and gravity acceleration found in everyday life. Therefore, all the relativistic corrections to Newtonian mechanics in the Earth system are negligible. Both, for the internal operations of the climate and for the evolution of its orbital parameters on timescales of hundreds of millennia or shorter.

One effect, would be the minor role that apsidal precession have on the change of distribution of incoming solar energy described by the Milankovic cycles. But that can arguably considered negligible.

But perhaps the most important contribution would be the influence of relativistic corrections in Earth's orbit eccentricity variations on multi-million years timescales.

State-of-the-art orbital solutions for the long-term motion of the Earth like La2010, do use relativistic correction, however they are rather small. The way the corrections are included in the model are described by Saha & Tremaine (1994), where they point that:

  General relativistic effects in planetary motion have fractional
  amplitude of order $\frac{k^2}{c^2 r} \sim 10^{-8}$ at $r = 1 \,  \textbf{AU}$.

Meaning that the correction correspond to a 0.000001% of the total variation of the orbital parameters. Unquestionably, even such small corrections have a cumulative effect over multi-million years timescales. Varadi et. at. (2003), compares the output of a model using relativistic corrections (solid line) with one not using them (dashed line), and the following figure show the results over 3 million years, where can be observed that significant differences arise after 300,000 years.

However, it is reasonable to consider that such small corrections would have been overcome at some point in the past by some other unaccounted effects, like large meteorite impacts (or fly-by), solar storms, etc. Remember that La2010 go back 50 million years and other models go back several billion years, when such events were rather common. So, I would still argue that relativistic corrections are not very significant. However, in a chaotic system like Earth's climate, you can never rule out that a negligible forcing could have had an important effect.

Of course the answer would be different (and the relative importance higher) if we consider a planet orbiting extremely close to a super-massive star. But, I'm assuming you are mostly considering planets similar to Earth in that regard.

There are also some claims (the Damhsa Theory) that gravitational waves might have play a role in the very long term climate evolution of Earth. However, I'm not capable to really assess the validity of such theory, but I have to admit I'm skeptical about it. I've posted a question about that in Physics SE, an there seem to be wide consensus that such effect would be exceedingly small to ever deserve any kind of consideration.


The green material indicates the potential presence of copper & the shiny bits on the lower left & mid right of the specimen look metallic, but that could be just glint in the picture.

Also, there are two groves on the lower right which may indicate a soft metal like copper.

If it is metallic it could be native copper or it could be lump of copper from a foundry.


Does anyone know of a DBMS with global geospatial search?

The best open-source and free geospatial database is in my opinion PostGIS. It is easy to use and has a huge support group (also for example at  https://gis.stackexchange.com/)

It also connect to all sorts of different open-source programs and web-interfaces which should make data editing, viewing and sharing easy.

It can handle the date-line and the poles:

 4.2.3.2.
 What about the date-line and the poles?
 All the calculations have no conception of date-line or poles, the coordinates are spherical (longitude/latitude) so a shape that crosses the dateline is, from a calculation point of view, no different from any other shape.

(http://postgis.net/docs/manual-1.5/ch04.html#id358535)

Link: http://postgis.net/


Is Atacama Desert cloudy or cloudless most of the year?

The Atatacma desert comprise a very large area of more than 100,000 square kilometers, that host very different climates. The main factors driving the climatic variability are the distance to the Pacific ocean and elevation. This latter factor is very strong, as the Atacama desert covers a formidable elevation range, from sea level to almost 7,000 m, at the summit of Ojos del Salado, the highest volcano in the world.

The highest areas, that also happen to be further of the sea, are the driest and less cloudy. The weather pattern you mention of common foggy conditions only happens very close to the coast, extending inland only about 10 km or a few tens of kilometers trough low lying valleys. And is produced by fog that forms over the sea penetrate inland. It is called camanchaca, but it doesn't cross the coastal mountain range.

The pattern of cloudiness throughout the desert can be visualized using a dataset produced by NASA's Surface meteorology and Solar Energy, in particular the satellite derived Monthly Averaged Clear Sky Days (i.e. cloud cover less than 10%) over a 22-year period (July 1983 - June 2005). It has a resolution of 1°, so about 110 km here. That means that the central area of the desert is covered by just 12 cells, nevertheless it will be enough to see the pattern I mention.

The following figure shows the central section of the Atacama dessert using official IGM 1:500.000 maps in the left. And the mean clear skies dataset on the right for the very same area. The numbers refer to the 22-year mean clear sky days per month.

Now the interpretation will be easier if we overlay those two figures as in one as shown below:

From there you can see how there is a fairly large variability in the amount of clear sky days. From a few at the coast, to about a week over the coastal mountains to about two weeks east of the coastal mountains. Peaking at 17 days per month over the Salar de Atacama (a value surpassed only by the Sahara desert and the interior of Antarctica). Then, it is no coincidence that ALMA observatory, the largest radio telescope in the world, is located there, just east of the salar de Aatacama.

As mentioned before, topography is the main factor controlling this pattern. Even close to the coast, some mountain tops can have remarkable clear sky records, as is the case of the 2,635 m high Mount Paranal were the VLT observatory is located at just 15 km from the coast (falling on the lower left cell with 9 clear sky days in the figure above).

Finally, going back to your question: Both the astronomers and your geography text book are right, but each one is referring to a different area of the Atacama desert. And looking at the above data, it is right to say that the coastal part of the Atacama desert is cloudy most of the year. However, a fairly large area in the interior is cloudless most of the year.


If it rains harder, does it mean the rain's duration will be shorter?

The intensity of a rainstorm does not actually cause the duration of the precipitation to be shorter. There is a strong correlation, but not in the sense you may be implying here (let me get back to that in moment).
First you have to dispel the model that a cloud is a big container of water, and if it "rains harder", the cloud will run out of water quicker and the rain event will be shorter in duration. Rain doesn't really work like that.
The atmosphere everywhere (even outside the cloud) contains lots and lots and lots of water. And under a stable combination of temperature, pressure, and humidity, all that moisture is perfectly happy to exist in a completely gaseous state. But as differing air masses (different temperatures, pressure, and humidity) start to collide, the local atmospheric conditions can fall outside the range where water can exist in a completely gaseous state. That is known as the dew point.
A cloud is where two differing atmospheric conditions have met, and the resulting condensed water droplets simply do not have sufficient weight to overcome the updraft speed of the air around it. If the air masses mix slowly, the rate of condensation will occur slowly and over a longer period of time. The resulting clouds may simply "evaporate" as the local conditions stabilize, or the condensing water may slowly precipitate over the ground (gentle rain), or the precipitation may never reach the ground at all (virga). These gentler atmospheric changes tend to play out over longer periods of time because the air masses are moving more slowly so it takes longer for the differences to mix and settle down into a new steady state.
Here's the part where I talk about intensity
If two air masses have widely varying conditions (think warm moist air over the ocean meeting dryer hotter conditions over the land) and they meet more abruptly (higher wind speeds), this causes a more-violent disturbance; the moisture from the air will condense more quickly, the rain falls faster and harder, and the whole thing ends (relatively speaking) more quickly.
But the duration tends to be shorter because the reaction between the differing masses is occurring at a faster rate — so the whole event will generally play out more quickly. But it is perfectly conceivable that "harder rain" can last much longer if the storm system continues to pull in more of the moist atmosphere around it. In extreme circumstances, that's pretty much what a hurricane is; the storm itself gets so big that it starts to create it's own system that pulls in more and more atmosphere around it. The rain doesn't simply stop when all the rain has fallen out of the original clouds. It actually (continually) makes new clouds/precipitation as it continues to draw in the atmosphere surrounding it.
But speaking in broad generalities, the faster the disturbance occurs, the faster the moisture will condense, the harder the precipitation will fall, the more quickly the conditions will stabilize, and the duration of the rain will be less.


What is that spooky humming sound heard in earthquake footages?

Wailing sirens.

Examples 1, 2 where you see people come running out, i.e. exactly when you'd expect sirens, or 3, or 4 and 5 where they are explicitly mentioned.


Answer to this question is very well given at Physics forum pointed out by @gerrit. In short, Light should be strong enough in order to notice its colour by human eyes. Even on full moon night, light from the moon is 10 times less luminous than the dark limit of civil twilight hence we don't perceive sky color or even moon colour like we do during the day.


What factors bring sand into or out of the beach?

The amount of sand on the beach at any one time is a dynamic quasi-equilibrium between a whole raft of processes. These include wave power, frequency and direction, seabed angle, longshore drift, rips and undertow, wind strength, direction and continuity, fetch, coastal geomorphology, sediment availability, offshore currents, and probably other variables.

The entire system is too complex to summarize here, so I recommend Robin Davidson-Arnott's excellent book: 'An introduction to coastal processes and geomorphology'. Cambridge University Press, 2010.


The trouble with geothermal gradients is they are not the same everywhere. It is generally accepted that the geothermal gradient is 25-30 °C/km but there can be local variations. In South Australia the gradient is generally 30° C/km, but in the deeper parts of the Cooper Basin the gradient is 55-60 °C/km. Elsewhere, at a depth of 200 ft the temp is 11 C. In the UK the average geothermal gradient is 26 °C/km, but locally it can be in excess of 35°C/km.
With near surface depths, the ground temperature will vary with depth according to the time of day.

So to get an accurate geothermal map for your region would require localized data.


As you state, wind chill "is the cooling of a body due to the passing-flow of lower temperature air.

Because of this, wind chill only occurs when then air had capacity to absorb heat from a body - thus chilling the body. The capacity of air to absorb heat from a body is dependent on the temperature difference between the air and the body, and the humidity of the air.

In determining the ability of the air to absorb heat , the wet bulb temperature must be used, in conjunction with the dry bulb. Wind chill and [heat index] (https://en.wikipedia.org/wiki/Heat_index) are related.

In a hot environment, such as a very hot day in a desert, a wind chill factor usually will usually not exist. Under such conditions is it possible to a body to over heat and experience heat stress and hyperthermia, which can lead to death. Also, one has to be careful so that wind burn doesn't occur.


What does 'forcing' mean?

The PDSI is calculated from model output data. Models do not predict all relevant variables but some data need to be provided externally from the user. These externally provided data are denoted as "forcing" because they "force" the model to move in one direction (colloquially speaking). You might also call it "drive" a model -- but "to force" is the established expression in science.

In this case

In this particular case, the authors use observational data as input data for the model calculations. Therefore, the authors write

  The PDSI is calculated from a water-balance model forced with observed precipitation and temperature...

Other situations

One might force a model also with data from other models. A river run-off model might get input data from an atmospheric/meteorological model, which predicts precipitation and solar radiation at surface level. We could write

  The river run-off model ABC is forced by modeled precipitation and radiation of the XYZ meteorological model.


How does MSLP change with elevation? trying to interpolate MSLP

So the Mean Sea level pressure is defined (simply) as the pressure of the station, corrected to sea level. However, methodological problems occur over terrain, such as assumptions that may not be true.

A common method used to correct the pressure is called the barometric equation. One assumption, for example, is that the mean temperature of the previous 12 hours is used to determine the average temperature of the imaginary atmosphere (where the terrain actually is). Of course this generates problems, such as the idea that the mean temperature used is not representative, the lack of lapse rate information, etc. These problems can yield to extraordinary MSLP gradients that may or may not actually exist in reality.


Are there locations on Earth that only have one season?

Due to the obliquity of the Earth, no place would truly have a single season, which in this answer is taken as having consistent conditions, particularly in terms of temperature and precipitation.

An environment that would qualify as having minimal seasonality are in the equatorial tropics, which according to the article Climatic seasonality, resource bottlenecks,
and abundance of rainforest birds:
implications for global climate change (Williams and Middleton, 2008) due to the almost consistent insolation, as shown below:

Image source - the blue line represents the yearly trends across the year for  equatorial regions.

Although, according to the article, the temperature remains fairly constant, precipitation can have alternating wet and dry periods, and can affected by other climatic factors (depending on location) such as El Niño, monsoons etc.

However, according to the Köppen climate classification system, the closest environment that would have minimal seasonality is classified as Af, which are warm moist rainforest, located in the areas shown below:

Image source

An example of a location in such an environment is the city of Andagoya, Colombia, South America, (latitude 5N, elevation 65m) which has the following annual temperature and precipitation:

Image source: Climate Classification and Climatic Regions of the World, which describes the classification Af as lying within the influence of the Intertropical Convergence Zone (ITCZ) and experiencing very little variation in temperature and precipitation throughout the year.


What are the implications of the recent discovery that plants regulate their temperature around 21°C?

I am shooting a bit for the hip here to be honest, this answer is opinion, not a researched position, but...

To imply that a object, be it plant, animal, or inanimate object with the ability to self regulate their temperature has the ability to have implications on climate change on a global scale, at least a positive one, ignores the physical laws of entropy.  That statement assumes that by positive effects means slowing of warming.

Entropy as a basic rule of physics always increases.  For this purpose, you can consider entropy to be the total energy in the system, with the energy of concern here being "heat".  If a plant (or anything) raises its temperature, it also extracts that heat from somewhere else.  If the surrounding environment is warmer, it can do that by simply absorbing heat, otherwise it does that by using other energy by chemical or physical processes.  These processes always are net zero in entropy or increase entropy thus increase total system energy usually seen as heat.  The same is true when the plant needs to lower its temperature, it can exchange heat with surrounding environment or through physical or chemical means lower its temperature, but doing so will again either be net zero energy or an increase in energy/heat.

Plants do have an almost exemption of this rule though, they grow, and in doing so the store some energy, temporarily taking some of that energy out of the equation.  This stored energy, and thus heat, is then released when the plant dies and decays, is used as food, or when millions of years of the stored energy is used in the form of fossil fuels, again resulting in a net increase in total entropy in the system.

Plants can and are used for localized climate moderation, but the contribution that would be applied to their ability to regulate their own temperature I would think is somewhere between insignificant and a slight negative in terms of slowing global warming.  The more significant aspect is in areas like slowing ground heating of denuded areas, cleaning pollutants from the air, storing of energy for later use, and many other aspects of plant chemistry and relationship with its environment.  For instance, the shade provided by a single tree I would guess outweighs any effect cause by temperature regulation of many trees.  I would be happy to see any study to the contrary, but I do not see that as possible within the known laws of physics.


Are there natural-forcings climate projections over the 21st century?

You’re right that there were no future natural forcings experiments defined in the CMIP5 protocol.  The reason being simply that the modeling groups thought that other experiments were more deserving of their limited computing time.  Compare this with the much stronger call for the historicalNat and historicalGHG experiments, which were required for detection and attribution studies.  Individual modeling centers may have run future natural forcings experiments, but that will be hit and miss, and there wasn’t an experiment name to lodge the outputs to in the CMIP5 database.  Incidentally, the situation with the RCP (all forcings) experiments themselves was actually a bit imperfect, because the implementations of future natural forcings were left to the discretion of each modeling group:

  … It is recommended that either volcanic aerosols should be omitted entirely from the control and future runs, or, alternatively, the same background aerosol should be prescribed in both runs.
  It is recommended that some representation of the solar cycle be included in the 20th and 21st century simulations, though that is left up to the discretion of the modeling groups.

  Source: Taylor et al (2011).  A summary of the CMIP5 experiment design. (pdf)

There was a further recommendation for how future solar irradiance forcing should be represented:

  In CMIP5, climate projections were based on a stationary-Sun scenario, obtained by simply repeating solar cycle 23, which ran from April 1996 to June 2008 (Lean and Rind, 2009).

  Source: Matthes et al (2017).  Solar forcing for CMIP6 (v3.2), Geosci. Model Dev., 10, 2247-2302, https://doi.org/10.5194/gmd-10-2247-2017

But, in practice, groups did slightly different things from each other, so you usually have to check the output file metadata and any associated journal papers for individual model runs to get an idea of the details.

This is clearly not a crazy question though, because in CMIP6 some future natural forcings experiments have been defined, albeit in the lower priority tiers. Specifically, the Detection and Attribution MIP (DAMIP) includes ssp245-GHG and ssp245-nat experiments, and the volcano MIP (VolMIP) has the volc-cluster-21C experiment.  If you dig down into those you’ll find that future solar variability is derived more or less the way you describe, i.e., projecting forward based on a set of statistical time series models trained on past variability.  Note, however, that Matthes et al are careful to point out that this is a projection not a prediction:

  As of today, predicting solar activity up to 2300 is very challenging, if not impossible… The unusually long solar cycle number 23 that ended in 2009, and the weak one (no. 24) that followed came as a surprise, and manifested our evident lack of understanding of the solar cycle.

Conversely, future volcanic forcing in ssp245-nat will be prescribed as a near-constant background forcing:

  Volcanic forcing will be ramped up from the value at the end of the historical simulation period (2015) over 10 years to the same constant value prescribed for the piControl simulations in the DECK, and then will be kept fixed.

  Source: O'Neill et al (2016). The Scenario Model Intercomparison Project (ScenarioMIP) for CMIP6. Geosci. Model Dev., 9, 3461-3482, http://doi.org/10.5194/gmd-9-3461-2016

So why not a statistical model for volcanic emissions?  This forcing is episodic rather than cyclic and is prescribed to the CMIP models as several variables on latitude-height-time grids.  As you hint at in your question, this is too many degrees of freedom to pin down satisfactorily from just the 1850-2005 record.  Even if it could be done, you then have the problem of how to use the statistical model, given that each climate model will only run a few realisations of a particular projection.  Do you generate one scenario to be shared by all models, or do you let each group generate its own scenarios using the statistical model?  Either way, you can’t explore enough of the parameter space to avoid ending up with a CMIP6 ensemble containing decadal variability that is strongly influenced by forcing scenarios that are extremely unlikely to happen.

As I understand it, the current assumption is that volcanic forcing is stationary and, in the absence of knowing the future sequence of eruptions, its effect on slowly varying climate components like ocean heat content is best represented by a constant mean forcing.


What is the methodology to analyze future climatic extremes using the results of climate models?

Your question is fairly broad, and slightly vague so I don't know if I will be able to answer it in one go. If you would like any clarification, let me know.

How are predictions made?

The basic process generally used for probabilistic forecasting of the global climate is something like:

Take one or more general circulation models (GCMs), and run multiple simulations over the projection period.

GCMs are models that attempt to replicate the physics of the climate system, including land and ocean processes. They can not replicate the physics exactly, because:

they operate on scales of a few hundred meters at minimum, and so physical processes (which usually operate on much smaller scales) are scaled up and parameterised to work on the larger scale; and
because for some of the physical processes (especially those that have to be parametrised to larger scales), there is not enough data to adequately fit them. When this happens, those model parameters are usually calibrated - a large number of runs are made, with different values for those parameters, and then the best parameter values are chosen.

Usually, you run the model for some period prior to the projection period, so that you can compare that to observations (spin-up period).
You need to provide input data to the model. Mostly, this just consists of solar forcing (changes in the sun's output), as well as expected greenhouse gas (GHG) emissions, and aerosol emissions (both human and volcanic).
Simulation output is in the same format as your observational data, and generally includes all of the important variables - temperature, precipitation, etc.

Put all of those simulations in an ensemble.

Often, simulations are "bias corrected", which usually means they are changed so that the model average matches the observation average over some period prior to the projection period - this might be the last 30-40 years. This is to allow for model drift (which is mostly chaotic, and can happen in any direction).
The distribution of the simulations in the ensemble is used to create probabilistic projections. For example, each simulation has a mean global annual temperature. You could make the assumption that the errors in the simulations are normally distributed (over the ensemble), and so make an estimate of that distribution, and use that to make probabilistic estimates. This is basically saying that if ~50% of the models are over a certain temperature, you expect that (assuming the models, the input data, and assumptions they are based on are reliable*) there's a 50% chance that the global annual temperature of the earth would be over that temperature. A similar process can be used for the maximum temperature, or any other variable, and any statistics, including extremes indices. None of these predictions is a single value - they are always probabilistic, although it's probably quite common for only the mean of that distribution to be reported.
How you combine the information from the simulations in the ensemble is somewhat up to you. The basic method is as described above, and uses minimal assumptions about the data. It's also common for researchers to use a weighting methodology to estimate the ensemble mean, for example performance-based weighting, where models that perform better over the period before the projection are weighted more highly, with the assumption that they will perform better over the projection period too. Or you could weight based on model independence (if you're using multiple models), by weighting models that are less like other models more highly, in order to minimise bias from particular types of models (e.g. Bishop and Abramowitz 2013). [I have a paper in review at the moment that investigates the efficacy of some of these methods, I'll link to it when it comes out]
Can this process predict changes in 1000-year events? Yes, potentially, even when the projection period is usually more like 100 years. This is because 1 in 1000-year events are actually defined inversely - that is, they are thought to have a 0.1% chance of occurring in any given year. If your ensemble projects over 100 years, but has 100 simulations, then there are 10,000 years in which that a 1 in 1000 might occur. If you see it occurring 20 times, or 4 times, then you might get suspicious that things are changing. You probably need more than that to get a statistically significant result, but there are ensembles out there that are really big (e.g. Stainforth et al, 2005, which had 2,578 simulations totalling over 100,000 simulated
years, and  I think some of the ClimatePrediction.net have tens of thousands of simulations). Even without those large ensembles, if you assume particular distributions of extreme events where probability is a simple function of extremeness (e.g. Log-normal distribution or similar), then you can probably say something about large extremes based on the change in behaviour of less extreme events. Unfortunately, I am not aware of any experiments that look at the likely changes to very extreme events.

* Model reliability is obviously a fairly active field of debate and research. Suckling and Smith (2012) indicates that GCM-based ensembles are better than basic statistical models, but probably not currently much better than some more advanced statistical models. However, that still means that they're at least on-par with the best options we have for forecasting, unless you're in to reading chicken entrails.

References

Bishop, C.H. & Abramowitz, G., 2013. Climate model dependence and the replicate Earth paradigm. Climate Dynamics, 41(3-4), pp.885–900. Available at: http://link.springer.com/article/10.1007/s00382-012-1610-y [Accessed September 17, 2013].
Stainforth, D.A. et al., 2005. Uncertainty in predictions of the climate response to rising levels of greenhouse gases. Nature, 433(7024), pp.403–406. Available at: http://www.nature.com/nature/journal/v433/n7024/abs/nature03301.html.
Suckling, E.B. & Smith, L.A., 2013. An Evaluation of Decadal Probability Forecasts from State-of-the-Art Climate Models*. Journal of Climate, 26(23), pp.9334–9347. Available at: http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00485.1 [Accessed January 8, 2015].


How will sea level rise be distributed across the globe?

There are many factors involved, so this is worth yet another answer. At the end of his/her answer aretxabaleta states:

  In general, the areas near the poles have a negative trend (sea level is dropping, not rising) because of the Glacial Isostatic Adjustment (GIA) as the crust is still rebounding from the previous glaciation. In mid-latitudes, on the other hand the sea level rise rates are maximum

In those locations however, there is a stronger effect:

The ice masses themselves exert a large gravitational pull on the surrounding water, resulting in a lowering of the sea level around those masses (Greenland, Antarctica) when the ice melts.
This may seem counter-intuitive, and is best explained by looking at what happens when the ice masses grow:

The gravitation of the growing mass pulls water towards it. The resulting sea level rise on the edges of the ice mass is therefore larger than the eustatic (global, uniform, across the world) sea level decrease that occurs because of the water moving into the ice. The effect is that near the ice mass, sea level actually rises, and far away it falls faster than 'expected'.

When the ice melts the reverse happens: sea level close to the ice mass will drop, sea level far away will rise more than 'expected'.

To give this some actual numbers:
The eustatic sea level rise corresponding to the melting of the Greenland and West Antarctic ice caps is both approx. 6 meters.
Here in Europe (I live in the Netherlands) however, the Greenland melt would 'only' result in approx. 3 meters rise, because that is relatively close, but the West Antarctic melt would result in something like 8-9 meters extra water.

This picture shows the relative effect calculated for water running of West Antarctica. You should read the numbers as a multiplication factor to apply to amount of sea level rise in the case of a uniform distribution.

  Sea level change associated with a uniform thinning of the West Antarctic Ice Sheet (WAIS). Their result, reproduced in Fig. 1(a), was normalized by the eustatic sea level change (i.e. the change computed assuming that the meltwater entered the present-day ocean uniformly). [...] The map shows a peak sea level rise greater than 25 per cent above the eustatic value in the north Pacific and more than 20 per cent above the eustatic in the north Atlantic and Indian Oceans. In addition, the sea level fall is greater than five times the eustatic amplitude in the ocean adjacent to the West Antarctic.

On the robustness of predictions of sea level fingerprints
J. X. Mitrovica, N. Gomez, E. Morrow, C. Hay, K. Latychev, M. E. Tamisiea
14 October 2011
DOI: 10.1111/j.1365-246X.2011.05090.x


How are spherulitic structures formed in basalt rock?

According to the image that you provided, what you are seeing are not spherulites, but rather epoxy bubbles. More on that later. I will first answer what are spherulites:

Spherical features observed in thin sections can form by several ways.

Devitrification - this is the recrystallisation of glass. I think it is more common in rhyolitic rocks than in basaltic rocks. As the glass is a non-stable amorphous phase, there is a solid state transition of the glass to quartz or feldspars. The centre of the spherulite is usually some kind of an disturbance in the glass. Could be a crystal nuclei or a small bubble. Here is a magnificent example of a spherulite in rhyolite, from the beautiful collection of Bernardo Cesare:

Filling of amygdules - this usually happens in more basic rocks, for example basalts. A rounded cavity is left due to the presence of gas bubbles during solidification. In this case, the minerals grow from the walls of the cavity inwards, filling the empty space (in contrast to the inside to outside growth pattern of spherulites). The minerals that grow are usually zeolites, clays, quartz and various other hydrothermal minerals. I remember seeing a magnificent example of epidote filling an amygdule once in a basalt. Here's an example of an amygdule from the Imperial College Rock Library:

Notice how it doesn't completely fill in the gas cavity.

These are the two most common ways in which this can form. However, in your case I think the answer is less exciting than this. I am pretty sure that your rounded objects are simply bubbles in the epoxy. Here's why:

They are perfectly rounded. This rarely happens naturally.
They are completely empty.
The actual rock is to the left of that image. Most of the area covered in your image does not seem to have any real rock in it, unless it is glassy but I doubt it because there is rock on the left.
That 4-sided halo around it occurs almost entirely in artificial bubbles created during the sample preparation process. You can put it a λ plate and see that opposite sides have similar colours (either red or blue).


Is there a high-temperature, non-magnetic glue that doesn't dissolve in water?

Your question is quite similar to one that I asked some time ago, with the additional requirement that the glue be insoluble in water, which unfortunately excludes sodium and potassium silicate. Like you, I've found Ceramabond (albeit 571, not 569, in my case) to be too magnetic. I suspect that there's an element of random variation here. It's not (as far as I know) specifically formulated to be completely non-magnetic, so there may be some batches which are more magnetic than others. Khakhalova and Feinberg (2014) investigated some other high-temperature ceramic adhesives and found that they were also too magnetic for use with weakly magnetic samples. However, they do make one useful suggestion:

  It may be possible for rock and paleomagnetic labs to reduce the concentration of magnetic contamination in Omega cements, for
  example, by sending the powder through a very clean Franz magnetic separator
  multiple times.

I haven't yet heard of anyone actually doing this, but it certainly seems worth trying. They also write that

  We’ve contacted Omega Engineering Inc. regarding the iron concentrations in their
  cements and their technical staff are
  currently exploring whether it would be
  possible to produce a high purity, high
  temperature cement specifically for rock
  magnetic and paleomagnetic applications.

I don't know if anything has come of those attempts in the three years since the article was published, but you could email the authors and/or Omega to find out.

References

Khakhalova, Evgeniya and Feinberg, Josh M. (2014).
The iron that binds: The unexpectedly strong magnetism of high-temperature ceramic cements commonly used in rock magnetic experiments. IRM Quarterly, 24(2), url: http://www.irm.umn.edu/quarterly/irmq24-2.pdf


Is the Arctic already ice-free during summer?

You can follow the sea ice extent here at http://polarportal.dk/en/sea-ice-and-icebergs/

And here at http://nsidc.org/arcticseaicenews/

There is a lot of things you can not see in regular maps as they fill in the area with ice as open sea on their products,It is the same for land areas too they do not change the maps if the ground is covered by snow.

So the answer to your question,There is still an ice cover in the arctic even if it is starting to get dangerously low at the end of summer.

As a side note it does look like the arctic ice cover is melting a lot faster this year than what it have done the last ten years on average,You can see a more detailed and year by year graph here https://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/ for both arctic and antarctic sea ice


Why is this area colder than the surrounding hotter area?

The Himalayas and the Tibetan Plateau have high elevation and temperature drops with altitude up until the tropopause. The temperature on the map is measured and modeled on the land surface, regardless of elevation. You can also see that the temperatures in e.g. Ethiopia and the Caucasus Mountains are lower than surrounding lowlands.

At latitudes around 30 degrees (north and south), the air is dry and hot due to global circulation pattern. The weather patterns are also controlled by the topography, humid air can't pass the mountain range as it's forced to an altitude where the temperature force it to condensate. That is why the Gobi desert is hot and warm in the summer.

I hope this answers your question.


How much rain falls on the Earth each year?

That's a tricky question, it will vary from year to year but we can narrow it down with some assumptions so I can give an answer. The assumptions will be:

All precipitation over the sea will become liquid in contact with the sea surface and will be considered as rain.
Precipitation over Antarctica is negligible at a global scale.

The second one is pretty reasonable: look at the global distribution of precipitation on the era of satellite data (reference).

With these assumptions we only need to compute the amount of solid precipitation on land (outside Antarctica) and subtract it from the global total. And we can do so using the data provided by the Global Precipitation Climatology Centre, which provide both the global mean precipitation on land:

And the fraction of liquid precipitation on land:

I've downloaded both datasets in ASCII format, and computed that the mean percentage of liquid precipitation is 74.1%, but we can't use that value, because it might be strongly affected by areas with little precipitation. So if we compute a cell by cell total SOLID precipitation per year, and multiply that for the surface of a 1°x 1° cell (considering the effects of latitude), we get a total of solid precipitation for 2016 of 1.5e13 m³.

So with the additional assumption that 2016 was a representative year. That will take your total precipitation of 5.1e14 m³ per year to 5.0e14 m³ per year of RAIN only.

Perhaps we should have expected that there is not much of a difference given that most of the rainfall happen on the sea (The total precipitation on land for 2016 was 1.1e14 m³ meaning that the 13.6% was solid and 86.4% was rain).

Now if you want to consider snowfall over the sea, I don't know of a model with such output product. Therefore, you can make a simple model or make some assumptions to use Sea Surface Temperature to figure out if precipitation will turn to rain at some high above the surface.

But again, if you look at the map of global distribution of precipitation, the fraction coming from latitudes at which you could expect sea surface snow is rather small, so the correction coming from snowfall over the sea is likely to be a pretty small one too.


Why is there a bend in the Lomonosov Ridge?

Firstly, just including the map of the ridges, in particular the Lomonosov Ridge and the characteristic bend visible near the North Pole:

Image Source

Based on magnetic anomaly observations, Cochran et al. (2006) theorise that the bend visible in the Lomonosov Ridge formed over a 3-6 million year period where there may have been a non-transform offset connecting a seafloor spreading region in the west Eurasian Basin with the continued continental rifting to the east, that continued propogating eastward resulting in the area of oblique spreading.

According to the Cochran et al. article, the tectonic spreading occurred around 53-56 million years ago, which according to models from Shephard et al. (2013) was associated with the opening of the Eurasia Basin.

Note: Cochran et al. refer to the eastern side as that on the Siberian side of the 'bend' and consequently, the western side being in the direction of North America.

Specifically, Cochran et al. conclude that

  The prominent bend in the Lomonosov Ridge near the Pole corresponds to an approximately 50 km offset in Marvin Spur. The offset of the marginal ridge is consistent with the presence of a short extensional segment located between two long transforms.

References

Cochran et al. 2006, Morphology and structure of the Lomonosov Ridge, Arctic Ocean, Geochemistry, Geophysics, Geosystems

Shephard et al. 2013, The tectonic evolution of the Arctic since Pangea breakup:
Integrating constraints from surface geology and geophysics
with mantle structure Earth-Science Reviews


Does this peer-reviewed study (referenced in Forbes) contradict the accepted position that climate change is real?

I want to know if that article has been refuted anywhere

Yes. You can read all about it in the blog post
James Taylor misinterprets study by 180 degrees.

In short, the original paper was designed to test the view of "professional geologists", which in this case are members of the Association of Professional Engineers and Geoscientists of Alberta. The vast majority of them work in the fossil fuel industry. Therefore, those are people whose livelihood depends on the extraction of fossils fuels. This is not exactly the most unbiased crowd...

The article by James Taylor is spinning the original study into claiming that it applies to all geoscientists. The original authors of the study actually replied to Taylor's article saying:

  First and foremost, our study is not a representative survey. Although
  our data set is large and diverse enough for our research questions,
  it cannot be used for generalizations such as “respondents believe …”
  or “scientists don’t believe …”

(This is taken from a secondary source here)

In short, the article is not from "Forbes" (i.e., presenting the opinion of Forbes magazine). It was published in Forbes, but written by a lying climate denier. He has misinterpreted the original study, as evident by two independent analyses and by the reply of the authors themselves.

So to answer your question:

  Does this peer-reviewed study contradict the accepted position that climate change is real?

This peer-reviewed study does not contradict anything. Climate change is overwhelmingly accepted by all scientists. What this peer-reviewed study shows is that those who deny the realities of climate change are those employed by the fossil fuel industry, particularly people in top management positions.

Also, quoting myself from the comments:

  The study correctly showed that people employed by the fossil fuel
  industry tend to disagree that climate change is anthropogenic. The
  Forbes article generalised this to all scientists. This is wrong. The
  authors of the study said this is wrong.

I will finish with some anecdotes. I am a geoscientist at a top Australian University. Every single one of the scientists here accept the climate change is a major threat to modern human civilisation as we know it. In a previous university where many people were involved with fossil fuel research, people accepted the realities of climate change. They were involved with the research because they either tried to find better ways of fossil fuels (realising that renewables are not there yet, and nuclear is unfortunately not an option), or because they have to pay their rent and feed their children. None denied that climate change is real, and none denied that the fossil fuel industry is the leading cause of it. We geoscientists all understand that the major driving force of the fossil fuel industry and climate change denialism is political, financial (usually old white rich men who don't care about anything but their own monetary benefit) and not scientific.


Where to start with P190s Seismic Navigation Files?

It should be easy to spot the lat and lon coordinates. Have you found the spec? http://www.seg.org/documents/10161/77915/ukooa_p1_90.pdf


Craters actually can be identified by formation of high-pressure materials such as diamonds or stishovites and coesites (varieties of shocked quartz). A good example of this is the Popigai crater in Russia.

Pressures and temperatures at subduction zones are usually too low to form big diamonds but microdiamonds (10-80 microns) were discovered within metamorphic rocks related to continental collisions. There are five well confirmed diamond-bearing terranes, the Kokchetav massif of Kazakhstan, Dabie and Quinlin in China, the Western Gneiss Region of Norway, the Erzgebirge massif of Germany, and the Kimi complex of the Greek Rhodope (according to the paper http://www.pnas.org/content/104/22/9128.long).


Could the magnetic field influence tectonic forces

The electromagnetic force and related field is a strong force at very small distances (governs the way the proton and electron are held to an atom) but is relatively weak over large distances.  I don't see how that small force could act on processes involved in the convection of the mantle.  If memory serves, the iron in magmas preserves the force of the electromagnetic field on earth at the time the magma cools to form rock. It leaves its imprint but has no affect on the process or origin of magmatism much less the convection that drives plate tectonics


Well, kind of, depending on what you really mean.

We're being rather vague with our terms, and so it shouldn't be surprising if the answer doesn't meet our expectations.

We could interpret all these terms to conclude that such a situation will only rarely, or even never, happen.
But allowing some reasonable latitude (pardon the pun) in our definitions, we can come up with a reasonable response of "yes".

The Sun can only be "directly overhead" of one spot at a time, where the line between the Earth's center and the sun intersects the Earth's surface. Because the Earth is spinning on its axis and also moving in its orbit,  that spot is constantly changing latitude and longitude.

The Tropic of Cancer isn't a single-point "location" but a circle that stretches around the Earth.

At the exact moment of the summer solstice, the Sun is directly overhead one point on the Tropic of Cancer and one point only. That point slowly spirals down through the tropics until it reaches a corresponding point on the Tropic of Capricorn at the winter solstice. And then it begins the trip back up.

That's what happens in the geometrically-idealized definition of "directly overhead".  We can allow a small tolerance, and as the tolerance gets bigger, the spot of "direct overheadness" spreads out into a disk, which covers more and more of the Tropic of Cancer around the moment of the Solstice, due to the spot's E-W motion being much greater than its N-S motion.

Although the spot's change in latitude over time isn't linear , it's a reasonable approximation for this exercise.  The spot moves about 0.18 degrees north or south in a day, all the while circling the Earth. Around the Solstice it will move 0.09 degrees north and 0.09 south. The Sun's angular size in the sky is 0.5 degrees, so, it's reasonable to conclude that yes, the Sun is directly overhead every point of the Tropic of Cancer at some time around the summer solstice.

(The solstice does't always happen on June 21, but depending on the tolerance, some degree of direct-overheadness will be the situation  for a few days before and after the solstice).

So now, we get to your last two tricky terms: "noon" and "June 21" , which believe it or not are in conflict for this example.

There is a local "noon" (defined by when the Sun is the highest in the sky it can get) and a clock "noon" (defined by your time zone). Only people at lucky longitudes in their time zones get to have them coincide.  But "June 21" is defined by those very time zones.  And so the sun can be "directly overhead" at "noon" on June 21 only around those lucky meridians. Elsewhere the sun will be directly overhead at some time other than noon.


Pyroclastic density currents interpretation

The name of the cavities are lithophysae. They show that the current has high volatile content. Vapor phase devitrification is the origin of litophysae. Pyroclasts in the curremt maintain their volatile content till compaction. volatiles escapes from the clasts during deposition to the weakness zones of the flowage. After exsolution, the laminae (source of the volatile) will be compacted and vapor phase minerals tridymite, crystobalite and feldpspar crystallized.

The cavities don't have to be on the top of the pyroclastic density current. They may occur on the flowage shearing surfaces and a syn-depositional incident.

The answer is not complete but it may give some idea.


Why is the jet stream stronger in winter?

I'll look at the climates of the town of Inuvik In Canada's Northwest Territory at a latitude of 68°21′42″N against that of Mexico City at a latitude of 19°26'N. In July, the daily mean temperatures are 14.1°C in Inuvik and 18.2°C in Mexico City — a difference of 4.1°C.

Compare that small difference with the daily mean temperatures in January of -26.9°C in Inuvik and 14.6°C in Mexico City – a huge difference of 41.5°. That factor of ten increase in the temperature difference in winter over summer drives a lot more north-south circulation in the winter compared to the summer, which in turn makes the jet streams stronger in winter compared to summer.


Why are these patterns of scattered sunlight aligned to the local horizontal and vertical directions?

Note: All of the links in this answer point to various parts of Les Cowley's excellent Atmospheric Optics site. Les combines photographs, simulated images, and descriptions of the underlying physics to beautifully portray and explain a number of different optical effects in our atmosphere.

Note: The imagery on that site is copyrighted. Please do not edit this answer to portray images from that site.

That's a very nice picture that shows a number of ice halos. Ice crystal halos are caused by various shapes of ice crystals. Some of these halos such as the small circle that encircles the Sun in the image in the question are easily seen at all latitudes. Others only appear in very high latitudes, and even there they are rather infrequent.

The small circle is the 22° halo. This is a frequently seen halo, much more common than rainbows. It's caused by poorly aligned hexagonal prism ice crystals. If you look closely, you'll see that the sky is darker inside the 22° halo. This is similar to how the sky is darker outside the primary bow of a rainbow. Unlike a rainbow, the color separation is very small, making the 22° halo white rather than colored. If you look closely, you can see that the inner edge has a bit of a reddish tinge.

The two bright spots on the sides of the 22° halo are sun dogs. These result from hexagonal plates of ice with their large faces nearly horizontal. The curve the intersects the Sun, runs parallel to the horizon, and intersects the 22° halo at the sun dogs is the parhelic circle. Parhelic circles result from sunlight reflecting off nearly vertical faces of ice crystals. The mustache atop the 22° halo is the upper tangent arc. Tangent arcs result from ice crystals that form hexagonal columns rather than hexagonal plates. As is the case with the 22° halo, sun dogs, parhelic circles, and tangent arcs are fairly common.

The partial circle outside the 22° halo is the not so common supralateral arc, or possibly the even rarer 46° halo. Atop that is the circumzenithal arc.


Does the configuration of a confined layer change the storage?

Under normal conditions a layer of gravel has more hydraulic conductivity in comparison to sand. Check this table with a hydraulic conductivity k per soiltype

The storage in the aquifer with gravel will be larger than in sand if the same thickness is used. Otherwise you should take the thickness into account as well (= Transmissivity: kD).


How does soil fertility differ between Scandinavia and Russia

I don't know much about Scandinavia in the 1500's, and in particular, how much was forested. However, one can say that the whole area was previously glaciated, with much of the topsoil being eroded away by ice, so soils generally tend to be thin, immature, sandy and nutrient poor. We do know that conifers predominated, leaving a soil-litter of pine needles. This latter has a high cation exchange capacity that leads to acid flushes whenever it rains after a long dry period. This acidity tends to leach out nutrients and adds small concentrations of toxic metals. These conditions do not help the soil's fertility. In addition, the valley floors often accumulate peat, hence high organic carbon and acidity.
The geology of Scandinavia is complex, and difficult to generalize. Periglacial outwash in Sweden and Denmark would have given rise to some fertile areas, especially where there is limestone to counteract the tendency to acidity. So compared to Russia, Scandinavian soil and agricultural potential is more variable.
As regards climate, coastal Norway is much warmer than either eastern Scandinavia and Russia on account of proximity to the Gulf Stream Drift. It also has higher rainfall, so the effective growing season is longer. Northern Scandinavia and Russia have close to 24 hours sunlight per day in high summer, so one wonders whether two growing seasons per year for some crops might be feasible? Are there any agronomists out there who can advise on this question?


Maximum temperature possible on earth on a day

Maximum temperature over what area? There are of course local hot spots at hydrothermal and volcanic centers which far exceed the generally excepted maximum recorded temperature, of 58 deg C in Libya (as you correctly state). Many other high temperature anomalous areas exist in areas where there are no met sites to record them. For example, in the Afar triangle depression in the horn of Africa, or in the foothills of the Jebel Akhdar in Oman. In the latter case the steep slopes of black harzburgite rock re-radiates high summer insolation to well into the 50s, but as far as I know, the maximum temperature has never been investigated. Then there is the time-scale. Global warming will almost certainly increase the maximum recorded temperatures over the coming decades and centuries.

On the geological time scale, the sun's radiance is very slowly increasing, so it is only a matter of time (billions of years) before the planet gets so hot that photosynthesis will cease - in which case whatever humanity evolves into will eventually fry.


The problem is the increase in the rate of sea level rise. I pulled out some approximate numbers from the figure you presented:

Can you see now how the sea level is rising much faster today than a century ago?

Sea level rise, as well as climate change are normal things on Earth history. However, most times they happen at a very slow rate, allowing ecosystems and other processes to adapt to the change.

For example, if the climate changes over several hundreds of years, animals and even tree populations can "move" towards the side of their distribution where climate is still good for them. But if the climate changes in 50 years, all the trees can die before they had time to grow in the areas where they could thrive in the new climate.

In the case of sea level rise. The delta of a river for example, stays in equilibrium with the sea level because of the accumulation of sediments carried by the river. If the sea level rises slowly, the sediments can fill the delta and keep it roughly at sea level. But if the see level rises too quick for the sedimentation to keep up, it will be flooded by the sea, killing all the animals and people that live on such fertile environments.

Analogously, coastal infrastructure have a given lifetime. Let's say 50 years. If the sea level doesn't change much over that period (8.5 cm at the 1880-1940 rate), there is no problem. Once the infrastructure gets replaced, the new building will be set a bit higher.
However, in the next 50 years the sea level could rise 50 cm, or even more (it would be 19 cm if we assume the last rate from the figure won't increase any further), and that is a big deal. That could mean that much coastal infrastructure will be flooded, and maybe destroyed during storms.

In places like Bangladesh there are hundred of millions of people that could be displaced due to sea level rise if the rate keeps increasing. People that will also need to find a new home.

Coastal infrastructure loss, coastal erosion and immigration could be some of the worst expressions of fast sea level rise.

ADDITION

Given the interest risen by this question I'm adding here some data beyond what is presented by the OP, and brought to my attention by @Bobson in the comments. It comes from the paper Recent global sea level acceleration started over 200 years ago? and shows a sea level reconstruction going back to 1700, and it shows also the changes in rate over that period. This is summarized in their figure 3:

Here you can clearly see how, with some ups and downs, the rate of sea level rise have been increasing over the last few centuries. And notably the current rate, about 20 years after the end of this plot is already out of the scale, and around 3.2 mm/year as pointed also by other answers.

I would highlight the following from their abstract:

  Sea level rose by 6 cm during the 19th century and 19 cm in the 20th
  century.Superimposed on the long-term acceleration are quasi-periodic
  fluctuations with a period of about 60 years. If the conditions that
  established the acceleration continue,then sea level will rise 34 cm
  over the 21st century. Longtime constants in oceanic heat content and
  increased ice sheet melting imply  that  the latest
  Intergovernmental Panel on Climate Change (IPCC) estimates of sea
  level are probably too low.

Regarding to whether this is caused by humans or not, I rather stay out of that argument and point that our best science and models suggest that lowering $\text{CO}_2$ emissions can make a significant impact in slowing down sea level rise in the upcoming centuries, so we should ACT NOW, and stop arguing whether it was or not our fault in the first place.


Are the other causes of an earthquake (e.g. volcanic eruptions) the cause of the "sudden slip" which is the main cause of an earthquake?

When you look at a table of all the major historic earthquakes they are all related to plate tectonics, either directly or indirectly. These are all of the magnitude 7 to 9 events, and most of the magnitude 4 to 6 events. The linkage with volcanic eruptions is real, but weak. Again, most but not all, of the world's volcanoes are generated by plate tectonic processes, the main exceptions being intra-plate movement over mantle hot spots. As we get down to lesser magnitudes we are getting into greater frequencies. It is roughly a logarithmic relation ship, so for every major earthquake, there are thousands of low to medium level earthquakes and millions of small micro-seismic events - the latter being so small that nobody notices - except for geophysicists. There is a host of processes which give rise to low-level seismicity, such as submarine slope failures, turbidites, sedimentary compaction, thermal contraction, magma redistribution at depth, erosive load shedding, after-shock adjustments, landslides, mudslides, rock-falls, rapid draw-down in reservoirs, mining subsidence, fracking, and probably a load of other stuff that I can't think of right now.

So it's roughly a matter of scale. The USGS is correct that serious earthquakes are all caused by plate tectonics. On the other hand, your other source was right, that some seismicity can be caused in a multitude of ways.

Afterthought: Probably someone will point out very rare exceptions, such as major bolides crashing into Earth and causing shock waves right through the planet. But such are extremely abnormal.


The plates are not as rigid as you think. You seem to be imagining the situation as something like this: I boil an egg and take the shell off in pieces, but I can't take a piece of shell from the end and make it lay flat on the side of the egg. However, rock is not that rigid on scales of thousands of kilometres and millions of years (I don't think there exists any material which would be that rigid). Also, Earth's equatorial bulge is tiny relative to its diameter -- less than 50km. Tectonic plates move very slowly, and there is plenty of time for them to deform as they move.


Is a complete global flood physically possible on Earth?

Just to add some further discussion to @Pont and @fre0n excellent answers.

The problem of the water needed to submerge the world during the Genesis flood have been discussed for centuries. The narrative could seem legit as  traces of marine condition can be seen even in high mountains. The Biblical flood was the most logic explanation for marine fossils and wave patterns far away from any coast. Moreover, at the time when the Bible was written in the Levant, there might still have been a collective memory of sudden sea level rise from the possible opening of Bosporus and flooding of the Black Sea. Other experiences, as tsunamis formed in the tectonic active Eastern Mediterranean would also add to the idea of flooding as a divine respond to human actions.

Early scientists that described and compared features in the nature, e.g. Ibn-Sinaa, could also see that some rocks was formed by water. They added the superposition principle, that younger rocks are situated above older rocks and that the processes that formed the rocks continues today and must have taken long time. What they could see, describe and test was a continuation of the earlier ideas of flooding, but they used reason instead of dogma. Modern disciplines of science, as radiometric dating and taxonomy, have further refined our understanding of time and the relation between water and dry ground, but we are still building on the traditions of earlier scholars as Ibn-Sinaa. Sometimes we prove them wrong, just like future scientists will (hopefully) prove us wrong, but the human wish to understand the nature around us can easily be traced back to Old Testament and before.

Sea levels are constantly changing during the history of Earth. There is a number of parameters that controls the global sea level, some are slow but have a large impact. E.g. during Ordovician, the sea level might have been 3-400m higher than today. Not enough to reach the foot of modern Mt Ararat, but the planet was certainly more blue when the first fishes appeared. Also during Cretaceous, the sea level was 2-300m higher than today and more recent, in early Holocene, the sea level was 120m lower than today. Our ancestors could walk (and maybe a short swim or paddle) from Asia to Alaska, from Java to Australia, and across the Black Sea.

So where did the water go? At colder conditions water can be be trapped in ice shields, glaciers. Antarctica and Greenland holds a rather large fraction of the global fresh water. But most water are in the oceans, and larger sea level changes must be caused by changes of the oceans.

The oceanic crust is, relatively to the continental crust, thin and soft, but get harder and chemically heavier with age. The oceanic crust press down the asthenosphere and this results in more space for water, and the sea level sinks (in relation to the geoid). Mid-ocean volcanism on the other hand lifts the seafloor and forces the sea level to rise. Temperature of water is also a factor to consider. Warm water is has less density and occupies larger volume.

The total change in sea level in the past 500 million years have been estimated to about 500m, this is impressive, but far more than the 3,896m of Mt Ararat, that was supposed to be covered in the Genesis flood narrative. As mentioned, there might be more water trapped in the mantle transition zone, but it's hard to see how it could have slipped out to form liquid water, and even more difficult, how it could get back to the mantle, against gravity, after the flood.

However, as a homage to the Biblical believes, there could be an interesting link between sea level changes and mass extinction. Changing sea levels, especially when it happens rapidly, results in new conditions that species might not have time to adapt to. The connection is discussed in this article by Hallam and Wignall, 1999 (Mass extinctions and sea-level changes). The article is also a good example of scientific methods and reason. The language in a scientific article might not be so colorful as in Genesis, but it can open a world far more complex and wonderful than any dogma.

Finally, a reading tip:
One solution is proposed in Umberto Eco's The Island of the Day Before, maybe the water was borrowed from another day, as the Earth contains two days, separated by the date line.


No, this is not enough.

Relative humidity is defined as the water vapour partial pressure relative relative to the saturation water vapour pressure:

$$
\phi  =  {{e_w} \over {{e^*}_w}}
$$

where ${e^*}_w$ is the equilibrium vapour pressure (which may be relative to either liquid water, or to ice), and $e_w$ is the partial pressure of water.

${e^*}_w$ can be calculated using the Clausius-Clapeyron relation, but to get $e_w$ you need some information on the water content.  This information may come in many forms:

Water vapour mixing ratio (the number of water molecules per unit volume)
Specific humidity (the mass of water per unit volume)
Partial pressure of water vapour ($e_w$)
Dew point, which is the temperature at which $e_w = e^*_w$.

The one you are most likely to find on meteorology websites is the dew point temperature.  Basically, if you have two of temperature, dew point temperature, and relative humidity, you can calculate the third.  For example, see this University of Miami calculator.


How is relative humidity determined from a wet and dry bulb readings?

Edit: 1 May 2021
The following procedure uses the less accurate method from page 455 onward from the scanned sections of the book pictured below, from the original answer.
The procedure is a multistage process ideally suited to either a spreadsheet or programming code.
The equations use SI units.
1. Calculate the saturated vapor pressure at the dry bulb temperature
This is done using the equation:
$P''_{ws} \ = \ 0.61078\ e\ ^{17.27T_{dry}/(273.3+T_{dry})} \ \ kPa$
Where $T_{dry}$ is the dry bulb temperature.
2. Calculate the saturated vapor pressure at the wet bulb temperature
This is done using the equation:
$P'_{ws} \ = \ 0.61078\ e\ ^{17.27T_{wet}/(273.3+T_{wet})} \ \ kPa$
Where $T_{wet}$ is the wet bulb temperature.
3. Calculate the moisture content of saturated air at the wet bulb temperature
Use the equation: $r_o \ = \ \frac{18.016 \ (1.0048)P'_{ws}} {28.9664 \ (P_{atm}-1.0048)P'_{ws}} \ \ kg/kg$
Where $P_{atm}$ is atmospheric pressure
4. Calculate the enthalpy of water vapor pressure at the wet bulb temperature
$H'_{wo} \ = \ -0.00000662 \ t_{wet}^3-0.000194 \ t_{wet}^2+1.8375 \ t_{wet}+2500.83 \ \ kJ/kg$
5. Calculate the enthalpy of liquid water at the wet bulb temperature
$H'_{wl} \ = \ 0.0000063 \ t_{wet}^3-0.000727 \ t_{wet}^2+4.2058 \ t_{wet}+0.03 \ \ kJ/kg$
6. Calculate the enthalpy of water vapor pressure at the dry bulb temperature
$H'_{wi} \ = \ -0.00000662 \ t_{dry}^3-0.000194 \ t_{dry}^2+1.8375 \ t_{dry}+2500.83 \ \ kJ/kg$
7. Calculate the moisture content of saturated air at the wet bulb temperature
$r \ = \ \frac{r_o*(H'_{wo}-H'_{wl})-(1.005 \ t_{dry}-1.005 \ t_{wet})}{(H'_{wi}-H'_{wl})} \ \ kg/kg$
8. Calculate the vapor pressure
$P_w \ = \ \frac{r \ P_{atm}} {1.0048 \ (18.016/28.9664+r)} \ \ kPa$
9. Calculate the relative humidity
$\phi \ = \ P_w/P''_{ws}$

Previous Answer - scans from relevant pages from reference book
I'm going to go old school with this one.
The following pictures are the relevant pages from: Environmental Engineering in South African Mines, The Mine Ventilation Society of South Africa, 1989, pp 451-455. They give the psychometric equations that are required to calculate relative humidity from wet & dry bulb temperatures.

For simplicity, I use the less accurate equations on p455, section 9.2.
As a slight diversion, the other way to measure wet & dry bulb temperatures is to use a whirling hygrometer. The wet bulb temperature is always read first because it will start to warm as soon as the hygrometer stops whirling.


How to calculate residence time for an element in a reservoir?

Steady state is when the size of the reservoirs doesn't change with time (because inflow=outflow). The size of each reservoir is the number inside the boxes and the flow rates are the numbers beside the arrows.
If you calculate the total inflow/outflow from each reservoir, you can use the relationship you did enunciate at the start of the question to easily calculate residence times.

However, according to the diagram those reservoirs are not in steady state. So either the question is ill posed, or you are supposed to make some approximations (or a more complex calculation, but I don't think that's the case).


Lake Manasarovar v.s. Lake Rakshastal: fresh-water v.s. salt-water

You pretty much answered the question yourself.  Lake Rakshastal, along with most of the lakes along the Tibetan plateau is, indeed an endorheic lake.  The important meaning of that term is that there is no outflow from that basin.  Water evaporates, but as with any evaporative process, the minerals in the water stay behind and become more concentrated.  Since Lake Manasrovar flows into Lake Rakshastal, the water that leaves takes the minerals in contains with it, leading to a much lesser concentration left behind as new water flows in, and, most importantly, out of that lake.


Where does the Amazon River really begin?

From an Earth Science standpoint, it's meaningless to ask about the "source" of a river in this way.  The "source" of a river is the rainfall within its drainage basin, which percolates down into groundwater, and the "river" appears where the land has eroded down below the water table.

The Amazon has an enormous drainage basin:

and every point in it is its "source" in some way.

The trouble with your question is that it asks about the "source" of a river in a way that you first have to define what you consider the "source". Does a stream begin where its name begins? Where water first permanently flows above ground? Most of the time? Some of the time? Anywhere there's a big enough pile of wet leaves?

In Brazil, the part of the river above its confluence with the Rio Negro at Manaus has its own name -- the Solimões, so you could say the "Amazon" proper begins at Manaus. But this is thousands of miles from the river's farthest upper reaches.

The Wikipedia article on the Amazon River has the following to say about its "farthest source":

  The headwaters of the Apurímac River on Nevado Mismi had been considered for nearly a century as the Amazon’s most distant source, until a 2014 study found it to be the Cordillera Rumi Cruz at the headwaters of the Mantaro River in Peru. The Mantaro and Apurímac join, and with other tributaries form the Ucayali River, which in turn meets the Marañón River upstream of Iquitos, Peru, to form what countries other than Brazil consider to be the main stem of the Amazon.

But because a tunnel associated with the Tablachaca Dam diverts water away from a big loop of the Mantaro River, effectively shortening it, all you'll ever get now is an argument about what's "really" the furthest source.


Why does the wind periodically change direction?

For the answer to why there is wind, see: Where does wind come from?

That establishes the forces at work driving the wind, namely:

non-linear advection of momentum
the pressure gradient force (PGF)
the Coriolis force
friction

Friction is less over water than over land, and so the wind will tend to flow more parallel to the isobars than they will over land at the earths surface.  The force balance between the PGF, Coriolis and friction is easy to conceptualize:

Image taken from University of Illinois at Urbana-Champaign, credits at http://ww2010.atmos.uiuc.edu/(Gh)/abt/aknw/dvlp.rxml

In this we can see that see that wind will flow with low pressure to its left, and cross the isobars slightly toward the low pressure.  The angle of the wind crossing the isobars is related to friction.  The direction of the wind is related to the orientation of the isobars and friction.  The speed of the wind is related to the spacing between isobars (close = fast, far = slow).

However, this only explains a steady-state wind in equilibrium, which is great for theoretical explanations but is too idealized for the real atmosphere.  In your observations on the lake, the flow is not steady-state and that pesky non-linear term is at work.

The lowest level of the atmosphere is called the boundary layer, and this extends from the surface to roughly 1 - 2 km.  During the daytime this boundary layer is "well mixed", which just means it has a uniform potential temperature and moisture profile and it is turbulent.  To really over-simply turbulence, consider swirling motions of different sizes.  At the largest sizes these swirls are the size of the depth of the boundary layer.  At the smallest sizes the swirls are on the scale of millimeters, and there are swirls at all of the intermediate sizes.

Let us just consider the biggest of the swirls.  The top of these swirls are at the top of the boundary layer where the wind is typically faster (it can be slightly faster, or much faster).  This swirl will mix some of this momentum down to the surface, at the bottom of the swirl.  These swirls are moving around as well, not sitting in one place.  Where the swirls are, there will be a different wind velocity than where they arent, and it will depend on the orientation of the wind, the swirl and the momentum being mixed downward to the surface.  If you were standing at one place, this would give you the effect you observe, winds that change direction and/or speed.

Now consider all of the different sizes of eddies doing this, and things become a mess (turbulence!).  On some days the this effect is small and you might just notice subtle changes in the wind, and on other days you might have strong gusts and "bumpy" air.

Finally, lets get back to the lake. The lake has a temperature flux and a momentum flux with the air above it, which produce changes in the wind.  All of this wind is moving mass around and the net result of this is that the wind is causing the pressure field to evolve, and these changes feedback into the wind.

The above effects can be rolled into the non-linear and friction terms in the momentum equation, which are the reasons that your observations of the wind periodically change directions.


When calculating flood recurrence intervals, do you use annual instantaneous peak flows?

I think you should just follow the guidelines provided by the USGS for this calculations (http://water.usgs.gov/osw/bulletin17b/dl_flow.pdf). From there you can read:

  "Flood events can be analyzed using either annual or partial-duration series. The annual flood series is based on the maximum flood peak for each year. A partial-duration series is obtained by taking all flood peaks equal to or greater than a predefined base flood".

They also provide a list of FAQs (http://water.usgs.gov/osw/bulletin17b/bulletin_17B.html) and a way to calculate them.


First, let me link a variety of popular science articles which can give you some background explanation. Here are Scientific American, Smithsonian, and Audubon magazines.

The 'smoking gun' evidence linking birds and dinosaurs is the evolution of feathers. Feathers are a feature that set the birds apart morphologically from the rest of the tetrapods, and indeed from the rest of all animals. All birds have feathers and nothing that isn't a bird has feathers. So a logical place to start looking for the origin of birds is the origin of feathers.

Since the dawn of modern paleontology, there had always suspected links between dinosaurs and birds due to the fossils of Archaeopteryx found in the 1860s. Thomas Huxley claimed the two groups were related as early as 1863. But it wasn't until recent decades that the fossil record started being filled in with definitive links between Archaeopteryx and therapod dinosaurs, such as more species intermediate between birds and therapods and fossil impressions indicating that some therapods had feathers.

The rest is just filled in by logical deduction, or Occam's Razor. There is clear evidence that all birds have feathers, and no other animals alive today have feathers. There is now clear evidence that therapods had very similar skeletons to birds with feathers about 150 million years ago. There is also evidence that many therapods had feathers, a trait otherwise confined to birds.

Let our null hypothesis be that the origin of birds is unknown, and our alternative hypothesis be that birds evolved from dinosaurs. Given the similarities noted above (and, keep in mind, the evidence is much stronger for scientists who specialize in this area), do you think there is enough evidence to reject the null hypothesis and conclude that birds evolved from dinosaurs? If not, are there any plausible alternative hypotheses?

The great thing about science is that you never have to take someone else's word for it. Everyone has the right to be a skeptic, just keep an open mind and look at the evidence and you can draw your own conclusions.


Effects of Centrifugal Force on Gravity Vectors?

I'm guessing I'm being sold a bridge with his numbers, but can't tell for sure.

You're being sold a bridge with his numbers. If he had done the math correctly he would have obtained a deflection of 33.58 cm at 45° geocentric latitude rather than 17.245 cm. The youtube comments show a number of errors. Two key errors are that the commenter assumes that

Local vertical points directly toward the center of the Earth.
Gravitational acceleration due to the Earth's mass points in the same direction.

What those youtube comments do show is that the Earth is not quite a sphere. A closer approximation is an oblate spheroid. That said, his comments fall into the wronger than wrong category. Quoting Isaac Asimov,

  When people thought the Earth was flat, they were wrong. When people thought the Earth was spherical, they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together.

Note that I qualified latitude in the above as geocentric. Geodesists have multiple concepts of latitude. Geocentric latitude is the angle between a line to the center of the Earth and the Earth's equatorial plane. Geodetic latitude is the angle between the normal to the reference ellipsoid and the Earth's equatorial plane. Yet another concept is astronomical latitude, which is the angle between true vertical and the Earth's equatorial plane.

The difference between geocentric and geodetic latitude is at its greatest at 45°. A geocentric latitude of 45° is equivalent to a geodetic latitude of 45° 11' 32.7". Converting that 11' 32.7" difference to radians and multiplying by 100 meters results in 33.58 cm. The difference between geodetic and astronomical latitude is called the deflection of the vertical (or vertical deflection). The deflection of the vertical is rather small, less than 2' (two minutes of arc) even in extremely mountainous terrain. Typical values are a few tens of arc seconds.

What this means is that an oblate spheroid is a better model of the Earth's shape than a sphere. That does not mean a flat Earth model is correct. The Earth's flattening (how squished the Earth is at the poles versus the at the equator) is rather small. The poles are 22 km closer to the center of the Earth than is the equator. Percentage-wise, that's a 0.345% difference.

The reason an oblate spheroid is a better model of the Earth's shape than a sphere is because the Earth is spinning. That spin does two things: It results in a centrifugal acceleration from the perspective of an observer fixed with respect to the rotating Earth, and it results in an equatorial bulge. If the Earth was a uniform density liquid, the spin would make the Earth naturally relax into an oblate spheroidal shape. "Straight down", the combined effects of gravitational and centrifugal acceleration (geodesists call this "gravity" to distinguish it from gravitation) would be exactly normal to the surface.


Is the ocean a carbon sink when considering only the biospheric component?

Yes, the marine biosphere is a carbon sink, and a very important one. It is known that the oceans produce more oxygen and biologically consume more carbon dioxide than all the tropical rainforests. This is done by microscopic blue-green algae, cyanobacteria and phytoplankton of many kinds. Also by green algae such as seaweeds, by sea grass meadows, and by coral reefs which are built of calcium carbonate synthesised by the corals themselves. Sea grass is an interesting plant, related to land grasses but able to survive and prosper in shallow seas where there is plenty of light and suitable soil. It is very important for the marine ecosphere. As on land, there are marine deserts where there is very little biological activity, and other areas that are teeming with life.

The question arises of how much of this captured carbon remains in the sea. The answer is most of it, but it is impossible to give exact figures. Some of the marine biomass is removed by various means, fishing for example, but that does not mean that all the carbon is returned to the atmosphere. Sea birds consume a lot of fish, and much of their guano is deposited on land, and some of them die on land, but again not all the carbon is returned to the atmosphere. There are enormous deposits of guano on the coast of South America and some Pacific islands, which are mined for fertiliser. The bodies of dead marine creatures, and sometimes live ones, are often consumed by other marine creatures. A dead whale, for example, provides a feast for all sorts of marine carnivores and scavengers. Much of the marine biomass eventually sinks to the ocean floor, where it becomes part of the ooze and sediment.


The top expression is basically the depth-averaged velocity. Meanwhile the second expression only applies to geostrophic flows. The depth-averaged velocity can be caused by many mechanisms, with the geostrophic balance being one of them. The most common ones are the wind and the tides (but also differences in atmospheric pressure, sloping bottoms, ...). Both tides and wind create a barotropic pressure gradient that has to be compensated by other forces in the Navier-Stokes equations, with friction being the most common one. The geostrophic balance is a specific solution of the NS equations that neglects the effects of friction and any other forces. John Wilkin (Rutgers) has some good notes on how to estimate these currents from observations.

The barotropic pressure gradient is also the integral result for the entire water column. A good illustration is the thermal wind example:  You need a difference in slope between isobaric (pressure) and isopycnal (density) surfaces to give you a baroclinic gradient. In theory in a barotropic fluid the flow is the same at all depths: $u(z)=u_{bt}$. Clearly, in practice, any fluid will have boundary layers in which that is not the case.