If one body represents the international scientific consensus on global warming, it is the Intergovernmental Panel on Climate Change, a United Nations panel that just released the first portion of its fifth authoritative report on the science.
The report’s headline finding is that “it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”
It’s not just that the planet has warmed over the course of many decades, during which people have released massive amounts of greenhouse gases into the atmosphere. Among many other things, there is what scientists have called a “human fingerprint” — a pattern of warming in the troposphere and cooling in the stratosphere that is very likely characteristic of human influence.
The authors did not shrink from addressing one of the primary threads that critics have been pulling in their effort to unravel the scientific consensus — the recent flattening of global temperature rise.
“Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850,” the IPCC notes.
Nevertheless, a detectable slowing of the warming trend between 1998 and 2012 might well have to do with recent volcanic eruptions, which add heat-reflective materials to the atmosphere, a decade-long solar cycle and simple decade-to-decade variability.
The experts should keep working to refine their picture of the climate system, with the caution and skepticism that good science demands. Meanwhile, America’s leaders should not take the fruit of that skepticism — some continuing uncertainty — as license to continue stalling. Ignoring the real possibility of large increases in global temperature is not wise leadership. It’s wishful thinking.
The Washington Post (Oct. 9)