The United States faces the potential for abrupt climate change in the 21st century that could pose clear risks to society in terms of our ability to adapt.
"Abrupt" changes can occur over decades or less, persist for decades more, and cause substantial disruptions to human and natural systems.
A new report, based on an assessment of published science literature, makes the following conclusions about the potential for abrupt climate changes from global warming during this century.
* Climate model simulations and observations suggest that rapid and sustained September arctic sea ice loss is likely in the 21st century.
* The southwestern United States may be beginning an abrupt period of increased drought.
* It is very likely that the northward flow of warm water in the upper layers of the Atlantic Ocean, which has an important impact on the global climate system, will decrease by approximately 25-30 percent. However, it is very unlikely that this circulation will collapse or that the weakening will occur abruptly during the 21st century and beyond.
* An abrupt change in sea level is possible, but predictions are highly uncertain due to shortcomings in existing climate models.
* There is unlikely to be an abrupt release of methane, a powerful greenhouse gas, to the atmosphere from deposits in the earth. However, it is very likely that the pace of methane emissions will increase.
The U.S. Geological Survey led the new assessment, which was authored by a team of climate scientists from the federal government and academia. The report was commissioned by the U.S. Climate Change Science Program with contributions from the National Oceanic and Atmospheric Administration and the National Science Foundation.