Global ice-sheets are melting at an increased rate; Arctic sea-ice is disappearing much faster than recently projected, and future sea-level rise is now expected to be much higher than previously forecast, according to a new global scientific synthesis released today by some of the world's top climate scientists including Scripps Institution of Oceanography at UC San Diego climate scientist Richard Somerville.
In a special report called "The Copenhagen Diagnosis," 26 researchers, most of whom are authors of published IPCC reports, conclude that several important aspects of climate change are occurring at the high end or even beyond the expectations of only a few years ago.
"Carbon dioxide emissions cannot be allowed to continue to rise if humanity intends to limit the risk of unacceptable climate change. The task is urgent and the turning point must come soon. If we are to avoid more than two degrees Celsius (3.6 degrees Fahrenheit) warming, which many countries have already accepted as a goal, then emissions need to peak before 2020 and then decline rapidly," Somerville said.
The report also notes that global warming continues to track early IPCC projections based on greenhouse gas increases. Without significant mitigation, the report says global mean warming could reach as high as seven degrees Celsius (12.6 degrees Fahrenheit) by 2100.
The researchers will release the report two weeks before United Nations-led climate change talks begin in Copenhagen, Demark. The conference is anticipated to produce a successor or companion emissions agreement to the 1998 Kyoto Protocol, the first commitment period of which expires in 2012.
The Copenhagen Diagnosis, which was a year in the making, documents the key findings in climate change science since the publication of the landmark Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report in 2007.
The new evidence to have emerged includes:
• Satellite and direct measurements now demonstrate that both the Greenland and Antarctic ice-sheets are losing mass and contributing to sea level rise at an increasing rate.
• Arctic sea-ice has melted far beyond the expectations of climate models. For example, the area of summer sea-ice melt during 2007-2009 was about 40 percent greater than the average projection from the 2007 IPCC Fourth Assessment Report.
• Sea level has risen more than five centimeters over the past 15 years, about 80 percent higher than IPCC projections from 2001. Accounting for ice-sheets and glaciers, global sea-level rise may exceed one meter by 2100, with a rise of up to two meters considered an upper limit by this time. This is much higher than previously projected by the IPCC. Furthermore, beyond 2100, sea level rise of several meters must be expected over the next few centuries.
• In 2008 carbon dioxide emissions from fossil fuels were about 40 percent higher than those in 1990. Even if emissions do not grow beyond today's levels, within just 20 years the world will have used up the allowable emissions to have a reasonable chance of limiting warming to less than two degrees Celsius.
The report concludes that global emissions must peak then decline rapidly within the next five to ten years for the world to have a reasonable chance of avoiding the very worst impacts of climate change.
To stabilize climate, global emissions of carbon dioxide and other long-lived greenhouse gases need to reach near-zero well within this century, the report states.