Steam and smoke rises from a coal power station in Gelsenkirchen, Germany in 2009. Scientists are more confident than ever that pumping carbon dioxide into the air by burning fossil fuels is warming the planet. By how much is something governments and scientists meeting in Stockholm will try to pin down with as much precision as possible Sept. 27 in a seminal report on global warming.
AP Photo/Martin Meissner
STOCKHOLM — Scientists can now say with extreme confidence that human activity is the dominant cause of the global warming observed since the 1950s, a new report by an international scientific group said Friday. Calling man-made warming “extremely likely,” the Intergovernmental Panel on Climate Change used the strongest words yet on the issue as it adopted its assessment on the state of the climate system.
One of the most controversial subjects in the report was how to deal with a purported slowdown in warming in the past 15 years. Climate skeptics say this “hiatus” casts doubt on the scientific consensus on climate change. Many governments had objections over how the issue was treated in earlier drafts and some had called for it to be deleted altogether.
Many scientists say the purported slowdown reflects random climate fluctuations and an unusually hot year, 1998, picked as a starting point for charting temperatures. Another leading hypothesis is that heat is settling temporarily in the oceans, but that wasn’t included in the summary.
The IPCC said the evidence of climate change has grown thanks to more and better observations, a clearer understanding of the climate system and improved models to analyze the impact of rising temperatures.
“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 the concentrations of greenhouse gases have increased,” said Qin Dahe, co-chair of the working group that wrote the report.
The full 2,000-page report isn’t going to be released until Monday, but the summary for policymakers with the key findings was published Friday. It contained few surprises as many of the findings had been leaked in advance.
The IPCC assessments are important because they form the scientific basis of U.N. negotiations on a new climate deal. Governments are supposed to finish that agreement in 2015, but it’s unclear whether they will commit to the emissions cuts that scientists say will be necessary to keep the temperature below a limit at which the worst effects of climate change can be avoided.
Using four scenarios with different emissions controls, the report projected that global average temperatures would rise by 0.3 to 4.8 degrees C by the end of the century. That’s 0.5-8.6 F.
Only the lowest scenario, which was based on major cuts in CO2 emissions and is considered unlikely, came in below the 2-degree C (3.6 F) limit that countries have set as their target in the climate talks to avoid the worst impacts of warming.
“This is yet another wakeup call: Those who deny the science or choose excuses over action are playing with fire,” U.S. Secretary of State John Kerry said in a statement. “Once again, the science grows clearer, the case grows more compelling, and the costs of inaction grow beyond anything that anyone with conscience or common sense should be willing to even contemplate.”
At this point, emissions keep rising mainly due to rapid growth in China and other emerging economies. They say rich countries should take the lead on emissions cuts because they’ve pumped carbon into the atmosphere for longer. Climate activists said the report should spur governments to action.
Next year, the IPCC will adopt reports on the impacts of global warming, strategies to fight it and a synthesis of all three reports.