How quickly parts of the Earth's climate are changing in response to added greenhouse gases and what's forecast for decades ahead is a mixed bag, a federal advisory council says in a report out Tuesday.
For example, two "abrupt" impacts the National Research Council report said can be definitively linked to man-made climate change are a rapid decline in sea ice over the past decade, and increased extinction pressure on plant and animal species. (For this study, the definition of abrupt is on the scale of years or decades.)
Specifically, the report noted that late summer Arctic sea ice extent has decreased substantially since the satellite data record began in 1979, and has been particularly low over the past seven summers.
As for abrupt impacts on animals and plants,"biologically important climate attributes — such as the number of frost-free days, length and timing of growing seasons, and the frequency and intensity of extreme events — are changing so rapidly that some species can neither move nor adapt fast enough."
On the other hand, the study finds that some potential threats "are unlikely to take place over the near term." These include quick changes in ocean current circulation, destabilization of the Antarctic ice sheet, and a rapid release of methane and carbon that's currently trapped in northern ice and permafrost soil.
The probability of changes or disruptions to ocean currents, specifically one that was made infamous in the 2004 movie The Day after Tomorrow in which the climate changed dramatically in a matter of days, "is now understood to be low," the report noted. The same is true for concerns about rapid sea level rise from the melting of the Antarctic ice sheet, as well as the quick release of methane, a greenhouse gas that's locked in permafrost in the far north.
The report also stresses the importance of an abrupt change early warning system to prepare for quick climate changes: "Surprises in the climate system are inevitable: an early warning system could allow for the prediction and possible mitigation of such changes before their societal impacts are severe," the report states.
"Research has helped us begin to distinguish more imminent threats from those that are less likely to happen this century," said James W.C. White, professor of geological sciences at the University of Colorado, Boulder, and chairman of the committee that wrote the report.
"Evaluating climate changes and impacts in terms of their potential magnitude and the likelihood they will occur will help policymakers and communities make informed decisions about how to prepare for or adapt to them," he added.
"The time has come for us to quit talking and take action," White said at a news conference in Washington, D.C., on Tuesday.
The study was sponsored by the National Oceanic and Atmospheric Administration, National Science Foundation, U.S. intelligence community and the National Academies, which is made up of The National Academy of Sciences, National Academy of Engineering, Institute of Medicine and National Research Council.
This is a follow-up to a 2002 study by the National Academy of Sciences, "Abrupt Climate Change: Inevitable Surprises."