A pause in global warming does not disprove a human role in climate change

A pause in the pace of global warming does not invalidate research that links climate change to human activity, national science academies in the United States and the United Kingdom said in a joint report last week.

While the science in some areas of climate change continues to evolve, man’s contribution to warming, sea-level increases and the decline in Arctic sea ice is “more certain than ever,” according to the academies. The report by the top scientists in two countries is meant to answer common questions on climate change in language non-scientists can understand.

“Our expectation as scientists always was to see very complex changes in the average temperature of the planet, and that’s exactly what we see,” Benjamin Santer, research scientist at California’s Lawrence Livermore National Laboratory, said at a briefing. “The key point is that the stasis — slowdown — as people have termed it over the last 15 years, does not fundamentally invalidate our understanding of the human effects on climate.”

Temporary cooling from increased volcanic activity or other emissions does not undermine climate models that aim to predict the rate of warming, Santer said.

Global-warming skeptics seized on what the scientific community calls a “hiatus” in warming as evidence that concerns over warming are overblown. Temperatures on average worldwide rose at a rate of 0.05 degrees Celsius per decade from 1998 through 2012, according to a report from the United Nations Intergovernmental Panel on Climate Change. The rate was 0.12 degrees per decade from 1951 through 2012, the panel said, noting that “due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.”

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Keystone over the years

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January’s final environmental impact analysis from the State Department revived the debate over the pipeline, which would carry Canadian crude oil through the United States to Port Arthur, Tex.

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President Obama rejected a presidential permit for the Keystone XL pipeline, which would have carried Canadian crude oil through the United States to Port Arthur, Tex.

Canada's Keystone pipeline South of Fort McMurray, Alberta, swaths of trees were removed to make way for an underground oil pipeline that carries product from the oil sands mines to processing facilities. Most of the proposed Keystone XL pipeline will be underground as well. Michael S. Williamson/The Washington Post

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While the American Northeast experienced colder than normal temperatures in January, that month was the fourth-warmest January since 1990, according to Inez Fung, a professor of atmospheric science at the University of California at Berkeley. “There will always be cold nights and cold days, but what we expect is that they will be rarer and rarer,” Fung said.