Need different temperature change data sets explained Nasa's temperature record is showing temperature increase. When I confronted a climate change skeptic with it, he replied that the data has been tempered with, and that there are different data sets which do not show temperature increase.

The exact reply was:


  According to RSS, UAH and radiosonde global temp anomaly datasets,
  there hasn't been a global warming trend in 20 years;
  
  http://www.woodfortrees.org/plot/rss/from:1996.6/to:2015.7/plot/rss/from:1996.6/to:2015.7/trend/plot/esrl-co2/from:1996.6/to:2015.7/normalise/trend/plot/esrl-co2/from:1996.6/to:2015.7/normalise
  
  GISS and HADCRUT4 datasets have added heat to raw temperature data to
  artificially keep the warming trend going as NOAA freely admits:
  
  https://www.ncdc.noaa.gov/img/climate/research/ushcn/ts.ushcn_anom25_diffs_urb-raw_pg.gif


This sounds reasonable to me.

Can anyone familiar with climate science explain why there are several data-sets, and why they are saying different things, and why NASA's set is the correct one?
There are several climate datasets around the world, two in America - NASA's GISTEMP, and NOAA's MLOST, and one in the UK - HadCRUT. These are the main datasets but there are others around the world, China, Japan etc.

The datasets differ slightly in the starting date, number of met stations included, degree of interpolation, and the way they get round the problem of lack of met stations in oceanic areas. 

As to being 'tampered with', this is a subtle malicious implication that the data has been fudged. It is also an insult to the scientific integrity of the thousands of climate scientists involved, whose aim, as in all of science, is to get at the truth. Of course, the data have been 'processed'. This is an essential part of data quality control to interpolate missing data, and to ensure consistency of the data set. But no data has been 'tampered with' in the sense of trying to lead to false conclusions.
One of the striking features of all the global datasets is that, despite minor differences, they all show the same basic characteristics of an accelerating global temperature - the 'hockey stick graph'. 

There is much dishonesty about, but not with the climate scientists. It is the climate skeptics who are being dishonest (not to mention scientifically incompetent).