The good news: A big disruption of the Atlantic Ocean currents that bring warm water north—an idea taken to extremes in the 2004 climate armageddon flick The Day After Tomorrow—probably won't happen this century.
The bad news: Other "abrupt" climatic changes are big threats, some are already underway and the nation isn't ready.
A new National Research Council report on the topic urges the creation of an Abrupt Change Early Warning System to brace for fast-moving climatic shifts.
"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 says.
"Identifying key vulnerabilities can help guide efforts to increase resiliency and avoid large damages," adds the study, sponsored by the U.S. intelligence community, the National Oceanic and Atmospheric Administration, the National Academies and others.
The report catalogs some abrupt changes that are already happening and it casts a wider lens on the notion of "abrupt," to include gradual climate changes that can bring about rapid ecological or economic upheaval once they cross a threshold. Think melting permafrost destabilizing pipelines, rising sea levels topping sea walls, or rising ocean temperatures and acidity reaching tipping points that doom certain species.
"Right now we don't know what many of these thresholds are," James W.C. White, a professor of geological sciences at the University of Colorado and chair of the committee that wrote the report, said in a statement.
"But with better information, we will be able to anticipate some major changes before they occur and help reduce the potential consequences," White added.
Overall, the report examines over a dozen types of changes to oceans, lands and atmosphere. Some abrupt climate changes are happening already. They include increasing disappearance of late summer Arctic sea ice that could have "large and irreversible" effects, such as disruption of marine food webs and coastal erosion.
The same melting Arctic ice is bringing "new legal and political challenges" as sea lanes open and nations jockey for access to oil-and-gas supplies.
Also upon us: Increased extinction risks as species like polar bears struggle to adapt to changes in temperature and sea ice habitat that is crucial for hunting.
Other abrupt changes that may loom this century range from decreased ocean oxygen, which can threaten marine life, to more flooding and more intense and longer heatwaves. The latter two are already seeing a detectible trend, according to the report. The report's authors list those three as "moderate" risks this century with a "high" chance of significant change after 2100.
But the report also concludes that two ominous threats are unlikely to come to pass this century. One is disruption of the ocean currents called the Atlantic Meridional Overturning Circulation and changes it would bring to ocean and atmospheric temperatures and the ocean's ability to store heat and carbon.
The 2004 sci-fi movie used that idea as a launching pad for a plot about an instant ice-age in northern climates (not to mention some dramatic moments for the father-son duo played by Dennis Quaid and Jake Gyllenhaal).
But the report cites recent research showing that the current is stable and that an abrupt change "will not occur in this century."
The second disaster unlikely to happen this century is abrupt releases of carbon stored in high-latitude permafrost soils, and methane trapped in ocean sediments and permafrost. But that doesn't mean all is well with the trapped Arctic gases.
"According to current scientific understanding, Arctic carbon stores are poised to play a significant amplifying role in the century-scale buildup of carbon dioxide and methane in the atmosphere, but are unlikely to do so abruptly, i.e., on a timescale of one or a few decades," the report states.
"Although comforting, this conclusion is based on immature science and sparse monitoring capabilities. Basic research is required to assess the long-term stability of currently frozen Arctic and sub-Arctic soil stocks, and of the possibility of increasing the release of methane gas bubbles from currently frozen marine and terrestrial sediments, as temperatures rise," it adds.