By Karl Ritter
STOCKHOLM: Scientists working on a landmark U.N. report on climate change are struggling over how to address a wrinkle in the meteorological data that has given ammunition to global-warming skeptics: The heating of Earth’s surface appears to have slowed in the past 15 years even though greenhouse gas emissions keep rising.
For years, skeptics have touted what looks like a slowdown in surface warming since 1998 to cast doubt on the scientific consensus that humans are cooking the planet by burning coal, oil and natural gas.
Scientists and statisticians have dismissed the purported slowdown as a statistical mirage, arguing among other things that it reflects random climate fluctuations and an unusually hot year picked as the starting point for charting temperatures. They also say the data suggest the “missing” heat is simply settling — temporarily — in the ocean.
But as scientists study the issue, the notion of a slowdown has gained more mainstream attention, putting pressure on the authors of the new U.N. report to deal with it.
The Intergovernmental Panel on Climate Change report is expected to assert that global warming is continuing. It is also expected to affirm with greater certainty than ever before the link between global warming and human activity.
Leaked documents obtained by the Associated Press show there are deep concerns among governments over how to address the purported slowdown ahead of next week’s meeting of the IPCC.
“I think to not address it would be a problem because then you basically have the denialists saying, ‘Look, the IPCC is silent on this issue,’ ” said Alden Meyer of the Union of Concerned Scientists in Washington.
In a leaked June draft of the report’s summary for policymakers, the IPCC said that while the rate of warming between 1998 and 2012 was about half the average rate since 1951, the globe is still heating up. As for the apparent slowdown, it cited natural variability in the climate system, as well as cooling effects from volcanic eruptions and a downward phase in solar activity.
Many skeptics claim that the rise in global average temperatures stopped in the late 1990s, and their argument has gained momentum among some media and politicians.