A new government report has a dire warning for the Obama administration: The United States could suffer the effects of abrupt climate changes within decades—sooner than some previously thought.

The report says that seas could rise rapidly if melting of polar ice continues to outrun recent projections, and that an ongoing drought in the U.S. west could be the start of permanent drying for the region.

Many scientists are now raising the possibility that abrupt, according to the report, that catastrophic switches in natural systems may punctuate the steady rise in global temperatures now underway.

According to the report, the Intergovernmental Panel on Climate Change (IPCC) maximum estimate of two feet of sea level rise by 2100 may be exceeded, because new data shows that melting of polar ice sheets is accelerating.

Among other things, there is now good evidence that the Antarctic ice cap is losing overall mass. At the time of the IPCC report, scientists were uncertain whether collapses of ice shelves into the ocean off the western Antarctica were being offset by snow accumulation in the continent’s interior. But one coauthor, remote-sensing specialist Eric Rignot of the Jet Propulsion Laboratory, told a press conference at the meeting:  “There is a new consensus that Antarctica is losing mass.” Seaward flow of ice from Greenland is also accelerating. However, projections of how far sea levels might rise are “highly uncertain,” says the report, as researchers cannot say whether such losses will continue at the same rates.

In the interior United States, a widespread drought that began in the Southwest about 6 years ago could be the leading edge of a new climate regime for a wider region.

The researchers said two other systemic changes seem less imminent, but are still of concern. Vast quantities of methane, a potent greenhouse gas, have long been locked up in ocean sediments, wetlands and permafrost. These could be destabilized by climate change, leading to blowouts of gas, and thus even more abrupt temperature shifts.

The researchers also said blowouts appear unlikely in the next 100 years—but that steady emissions could double, especially in the north, as land and water warm up.

The researchers also looked at the continuous circulation of the Atlantic Ocean, which sends warm water northward and cold water southward, controlling the climate of western Europe and beyond. Some scientists say this circulation could collapse if enough northern ice melts and dilutes the salty water. The panel found this scenario unlikely in the short term, but warned that the circulation’s strength might decline 25% to 30% by 2100.

“Abrupt climate change presents potential risks for society that are poorly understood,” the researchers write. [There is an] urgent need for committed and sustained monitoring of those components [that] are particularly vulnerable.”