As climate change exceeds the worst projections, scientists underscore the urgency of reducing emissions.
By just about any measure, global warming is matching or exceeding experts' worst projections, and could bring drastic change to our planet, including a 19-foot sea level rise and the extinction of many species, according to a new report released today.
The study was published by 26 climate scientists, the majority of whom were authors of the Intergovernmental Panel on Climate Change report in 2007.
The researchers point to a gloomy slate of evidence: Carbon dioxide emissions are 40 percent higher than in 1990. Greenland and Antarctic ice sheets are melting at an accelerated pace. Sea level crept 80 percent higher over the last 15 years than projected in 2001. It is on track to rise twice as much by 2100 as the IPCC projected in 2007.
Arctic sea ice melted 40 percent more than the average prediction in the IPCC report.
"This stunned the scientific community because it was far greater than any projection," said climate scientist and study co-author Andrew Weaver of the University of Victoria in Canada's British Columbia.
"Things are happening faster and with greater magnitude than when the IPCC was published in 2007," Weaver said.
"We are in the lead-up to an historic climate summit -- the Copenhagen climate summit -- and it is absolutely essential that any policy making regarding climate change be based on the best and most up-to-date science," said co-author Michael Mann of Pennsylvania State University in State College.
Scientists have learned a lot since summer 2006 -- the cutoff for publication of research considered in the 2007 IPCC report. "What this report is an attempt to do is to provide an update of the current scientific understanding," Mann said.
"We are all concerned that we are basically on target for changes that are in general larger than what was projected from the IPCC report," he continued. "The observations are telling us that changes in many respects are happening faster than models projected."
Researchers have identified a global average temperature increase of about 3.6 degrees Fahrenheit as a threshold past which serious negative consequences are very likely. This amount of warming is close to the threshold for complete melting of Greenland and a resulting six-meter sea level increase, Weaver said.
"Something like 15 to 37 percent of all species become committed to extinction around (3.6 degrees Fahrenheit)," he added.
"In my opinion the single most important observation is that we are now able to quantify the amount of emissions we as humans can put in the air and stay below various temperature thresholds. What we can say now is climate cares about cumulative emissions and not emissions from any given year."
To avoid a 3.6 degree increase, immediate action is needed, the researchers said. Global emissions must peak within the coming decade and they most drop off rapidly after that.
"Among the things we've learned that we were not so sure of three years ago is that there is an urgency to this problem that isn't a political issue," said report author Richard Somerville of Scripps Institution of Oceanography at the University of California, San Diego. "It's Mother Nature herself."
The science that has emerged since the 2007 IPCC report appears to point to accelerating climate change, said Ken Caldeira of the Carnegie Institution of Washington in Stanford, Calif., who was not a part of the study.
"There is always a bit of a danger of over-interpreting things that have happened in the last couple of years," he said. "Yes, there is a big risk, and we'd better do something about it, but if all these things reverse in the next three years, that doesn't mean we don't need to do anything."
"Climate is about long term trends, not what's happened in the last three years," he added.