FILE - Smoke pours from a chimney at a cement plant in Binzhou city, in eastern China's Shandong province, Thursday, Jan. 17, 2013. Scientists from around the world have gathered in Stockholm in September... (Associated Press) 
 
 FILE - Smoke pours from a chimney at a cement plant in Binzhou city, in eastern China's Shandong province, Thursday, Jan. 17, 2013. Scientists from around the world have gathered in Stockholm in September... (Associated Press) 
 
 Top scientists from a variety of fields say they are about as certain that global warming is a real, man-made threat as they are that cigarettes kill. 
 
 They are as sure about climate change as they are about the age of the universe. They say they are more certain about climate change than they are that vitamins make you healthy or that dioxin in Superfund sites is dangerous. 
 
 They'll even put a number on how certain they are about climate change. But that number isn't 100 percent. It's 95 percent. 
 
 And for some non-scientists, that's just not good enough. 
 
 There's a mismatch between what scientists say about how certain they are and what the general public thinks the experts mean, experts say. 
 
 That is an issue because this week, scientists from around the world have gathered in Stockholm for a meeting of a U.N. panel on climate change, and they will probably issue a report saying it is "extremely likely" _ which they define in footnotes as 95 percent certain _ that humans are mostly to blame for temperatures that have climbed since 1951. 
 
 One climate scientist involved says the panel may even boost it in some places to "virtually certain" and 99 percent. 
 
 Some climate-change deniers have looked at 95 percent and scoffed. After all, most people wouldn't get on a plane that had only a 95 percent certainty of landing safely, risk experts say. 
 
 But in science, 95 percent certainty is often considered the gold standard for certainty. 
 
 "Uncertainty is inherent in every scientific judgment," said Johns Hopkins University epidemiologist Thomas Burke. "Will the sun come up in the morning?" Scientists know the answer is yes, but they can't really say so with 100 percent certainty because there are so many factors out there that are not quite understood or under control. 
 
 George Gray, director of the Center for Risk Science and Public Health at George Washington University, said that demanding absolute proof on things such as climate doesn't make sense. 
 
 "There's a group of people who seem to think that when scientists say they are uncertain, we shouldn't do anything," said Gray, who was chief scientist for the U.S. Environmental Protection Agency during the George W. Bush administration. "That's crazy. We're uncertain and we buy insurance." 
 
 With the U.N. panel about to weigh in on the effects of greenhouse gas emissions from the burning of oil, coal and gas, The Associated Press asked scientists who specialize in climate, physics, epidemiology, public health, statistics and risk just what in science is more certain than human-caused climate change, what is about the same, and what is less. 
 
 They said gravity is a good example of something more certain than climate change. Climate change "is not as sure as if you drop a stone it will hit the Earth," Princeton University climate scientist Michael Oppenheimer said. "It's not certain, but it's close." 
 
 Arizona State University physicist Lawrence Krauss said the 95 percent quoted for climate change is equivalent to the current certainty among physicists that the universe is 13.8 billion years old. 
 
 The president of the prestigious National Academy of Sciences, Ralph Cicerone, and more than a dozen other scientists contacted by the AP said the 95 percent certainty regarding climate change is most similar to the confidence scientists have in the decades' worth of evidence that cigarettes are deadly. 
 
 "What is understood does not violate any mechanism that we understand about cancer," while "statistics confirm what we know about cancer," said Cicerone, an atmospheric scientist. Add to that a "very high consensus" among scientists about the harm of tobacco, and it sounds similar to the case for climate change, he said. 
 
 But even the best study can be nitpicked because nothing is perfect, and that's the strategy of both tobacco defenders and climate deniers, said Stanton Glantz, a medicine professor at the University of California, San Francisco and director of its tobacco control research center. 
 
 George Washington's Gray said the 95 percent number the Intergovernmental Panel on Climate Change will probably adopt may not be realistic. In general, regardless of the field of research, experts tend to overestimate their confidence in their certainty, he said. Other experts said the 95 percent figure is too low. 
 
 Jeff Severinghaus, a geoscientist at the Scripps Institution of Oceanography, said that through the use of radioactive isotopes, scientists are more than 99 percent sure that much of the carbon in the air has human fingerprints on it. And because of basic physics, scientists are 99 percent certain that carbon traps heat in what is called the greenhouse effect. 
 
 But the role of nature and all sorts of other factors bring the number down to 95 percent when you want to say that the majority of the warming is human-caused, he said. 
 
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 Seth Borenstein can be followed at http://twitter.com/borenbears ||||| Media playback is unsupported on your device Media caption Climate change "threatens our planet, our only home", warns Thomas Stocker, IPCC co-chair 
 
 A landmark report says scientists are 95% certain that humans are the "dominant cause" of global warming since the 1950s. 
 
 The report by the UN's climate panel details the physical evidence behind climate change. 
 
 On the ground, in the air, in the oceans, global warming is "unequivocal", it explained. 
 
 It adds that a pause in warming over the past 15 years is too short to reflect long-term trends. 
 
 The panel warns that continued emissions of greenhouse gases will cause further warming and changes in all aspects of the climate system. 
 
 To contain these changes will require "substantial and sustained reductions of greenhouse gas emissions". 
 
 Image caption Projections are based on assumptions about how much greenhouse gases might be released 
 
 After a week of intense negotiations in the Swedish capital, the summary for policymakers on the physical science of global warming has finally been released. 
 
 The first part of an IPCC trilogy, due over the next 12 months, this dense, 36-page document is considered the most comprehensive statement on our understanding of the mechanics of a warming planet. 
 
 It states baldly that, since the 1950s, many of the observed changes in the climate system are "unprecedented over decades to millennia". 
 
 Document IPCC Summary for Policymakers [3MB] Most computers will open PDF documents automatically, but you may need Adobe Reader Download the reader here 
 
 Each of the last three decades has been successively warmer at the Earth's surface, and warmer than any period since 1850, and probably warmer than any time in the past 1,400 years. 
 
 "Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and that concentrations of greenhouse gases have increased," said Qin Dahe, co-chair of IPCC working group one, who produced the report. 
 
 Speaking at a news conference in the Swedish capital, Prof Thomas Stocker, another co-chair, said that climate change "challenges the two primary resources of humans and ecosystems, land and water. In short, it threatens our planet, our only home". 
 
 Since 1950, the report's authors say, humanity is clearly responsible for more than half of the observed increase in temperatures. 
 
 Media playback is unsupported on your device Media caption Dr Rajendra Pachauri said he was confident the report would convince the public on global climate change 
 
 But a so-called pause in the increase in temperatures in the period since 1998 is downplayed in the report. The scientists point out that this period began with a very hot El Nino year. 
 
 "Trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends," the report says. 
 
 Prof Stocker, added: "I'm afraid there is not a lot of public literature that allows us to delve deeper at the required depth of this emerging scientific question. 
 
 "For example, there are not sufficient observations of the uptake of heat, particularly into the deep ocean, that would be one of the possible mechanisms to explain this warming hiatus." 
 
 "Likewise we have insufficient data to adequately assess the forcing over the last 10-15 years to establish a relationship between the causes of the warming." 
 
 However, the report does alter a key figure from the 2007 study. The temperature range given for a doubling of CO2 in the atmosphere, called equilibrium climate sensitivity, was 2.0C to 4.5C in that report. 
 
 In the latest document, the range has been changed to 1.5C to 4.5C. The scientists say this reflects improved understanding, better temperature records and new estimates for the factors driving up temperatures. 
 
 What is the IPCC? In its own words, the IPCC is there "to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts". The offspring of two UN bodies, the World Meteorological Organization and the United Nations Environment Programme, it has issued four heavyweight assessment reports to date on the state of the climate. These are commissioned by the governments of 195 countries, essentially the entire world. These reports are critical in informing the climate policies adopted by these governments. The IPCC itself is a small organisation, run from Geneva with a full time staff of 12. All the scientists who are involved with it do so on a voluntary basis. 
 
 In the summary for policymakers, the scientists say the rise in ocean waters will proceed at a faster rate than we have experienced over the past 40 years. Global mean sea level rise for 2081−2100, the document says, is projected to be between 26cm (at the low end) and 82cm (at the high end), depending on the greenhouse emissions path this century. 
 
 The scientists say ocean warming dominates the increase in energy stored in the climate system, accounting for 90% of energy accumulated between 1971 and 2010. 
 
 For the future, the report states that warming is projected to continue under all scenarios. Model simulations indicate that global surface temperature change by the end of the 21st Century is likely to exceed 1.5 degrees Celsius, relative to 1850. 
 
 Prof Sir Brian Hoskins, from Imperial College London, told BBC News: "We are performing a very dangerous experiment with our planet, and I don't want my grandchildren to suffer the consequences of that experiment." 
 
 Follow Matt on Twitter. ||||| STOCKHOLM — The world’s top climate scientists on Friday formally embraced an upper limit on greenhouse gases for the first time, establishing a target level at which humanity must stop spewing them into the atmosphere or face irreversible climatic changes. They warned that the target is likely to be exceeded in a matter of decades unless steps are taken soon to reduce emissions. 
 
 Unveiling the latest United Nations assessment of climate science, the experts cited a litany of changes that were already under way, warned that they were likely to accelerate and expressed virtual certainty that human activity is the main cause. “Climate change is the greatest challenge of our time,” said Thomas F. Stocker, co-chairman of the Intergovernmental Panel on Climate Change, the United Nations-sponsored group of scientists that produced the report. “In short, it threatens our planet, our only home.” 
 
 The panel, in issuing its most definitive assessment yet of the risks of human-caused warming, hoped to give impetus to international negotiations toward a new climate treaty, which have languished in recent years in a swamp of technical and political disputes. The group made clear that time was not on the planet’s side if emissions continued unchecked. 
 
 “Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes,” the report said. “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.” 
 
 The new report is a 36-page summary for world leaders of a 900-page report that is to be released next week on the physical science of climate change. That will be followed by additional reports in 2014 on the most likely impacts and on possible steps to limit the damage. A draft of the summary leaked last month, and the final version did not change greatly, though it was edited for clarity. 
 
 Going well beyond its four previous analyses of the emissions problem, the panel endorsed a “carbon budget” for humanity — a limit on the amount of the primary greenhouse gas, carbon dioxide, that can be produced by industrial activities and the clearing of forests. No more than one trillion metric tons of carbon could be burned and the resulting gases released into the atmosphere, the panel found, if planetary warming is to be kept below 3.6 degrees Fahrenheit (2 degrees Celsius) above the level of preindustrial times. That temperature is a target above which scientists believe the most dangerous effects of climate change would begin to occur. 
 
 Just over a half-trillion tons have already been burned since the beginning of the Industrial Revolution, and at the rate energy consumption is growing, the trillionth ton will be burned sometime around 2040, according to calculations by Myles R. Allen, a scientist at the University of Oxford and one of the authors of the new report. More than three trillion tons of carbon are still left in the ground as fossil fuels. 
 
 Once the trillion-ton budget is exhausted, companies that wanted to keep burning fossil fuels would have to come up with ways to capture carbon dioxide and store it underground. In the United States, the Obama administration is moving forward with rules that would essentially require such technology, which is likely to be costly, for any future coal-burning power plants; the president’s Republican opponents have accused him of waging a “war on coal.” 
 
 The Intergovernmental Panel on Climate Change is a worldwide committee of hundreds of scientists that issues major reports every five or six years, advising governments on the latest knowledge on climate change. 
 
 The group has now issued five major reports since 1990, each of them finding greater certainty that the world is warming and greater likelihood that human activity is the chief cause. The new report finds a 95 to 100 percent chance that most of the warming of recent decades is human-caused, up from the 90 to 100 percent chance cited in the last report, in 2007. 
 
 But the new document also acknowledges that climate science still contains uncertainties, including the likely magnitude of the warming for a given level of emissions, the rate at which the ocean will rise, and the likelihood that plants and animals will be driven to extinction. The scientists emphasized, however, that those uncertainties cut in both directions and the only way to limit the risk is to limit emissions. 
 
 Climate-skeptic organizations assailed the new report as alarmist even before it was published. 
 
 The Heartland Institute, a Chicago organization, issued a document last week saying that any additional global warming would likely be limited to a few tenths of a degree and that this “would not represent a climate crisis.” 
 
 One issue much cited by the climate doubters is the slowdown in global warming that has occurred over the past 15 years. The report acknowledged that it was not fully understood, but said such pauses had occurred in the past and the natural variability of climate was a likely explanation.
– The UN's climate change panel for the first time charted the upper limit of acceptable global carbon emissions today—and we're already halfway to it. Based on an internationally agreed upon goal of keeping temperatures within 3.6 degrees Fahrenheit of their pre-industrial levels, humanity can only allow gas from 1 trillion tons of burned carbon to enter the atmosphere, the Intergovernmental Panel on Climate Change said in its report, according to the New York Times. We're on pace to hit that ceiling in 2040. The much-anticipated report was released this morning following a furious night of editing, but the substance of it hasn't changed much since a draft was released in August. The report also presents what, according to the BBC, is considered the most comprehensive statement on how climate change works, concluding with 95% certainty that human activity "has been the dominant cause" of the warming trend. That, the AP points out, is as certain as scientists are that cigarettes kill you, and more certain than they are that vitamins improve your health.