Sea Level Rise Predictions Too Low, No Abrupt Release of Methane: US Climate Change Science Program

thermohaline conveyor photo

image: NASA via Space and Astronautics News

Will abrupt climate change happen in the 21st century? The US Climate Change Science Program certainly considers that a possibility and has released a new report, appropriately titled Abrupt Climate Change, detailing its findings.

Defining 'abrupt' climate change as those which "can occur over decades or less, persist for decades or more, and cause substantially disruptions to human and natural systems," the report addresses four major questions (the possibility of abrupt changes in sea level, in land hydrology, in the Atlantic Meridional Overturning Circulation, and in atmospheric methane) and comes to the following conclusions:IPCC Sea Level Rise Predictions Very Likely Too Low
While the report says rapid and sustained arctic ice loss is likely in the 21st century, current models don't capture the recent rapid changes seen in Greenland and Antarctica. When these changes are included in climate change models it "will likely lead to sea-level projections for the end of the 21st century that substantially exceed the projections" presented in the latest IPCC report.

Extended Drought Likely in US Southwest
Although the report concludes that "there is no clear evidence to date of human-induced global climate change on North American precipitation amounts," it also says that subtropical aridity predicted in climate models is likely to intensify and extend into the US Southwest "potentially increasing the likelihood of severe and persistent drought there in the future." This drying may have already begun but cannot be definitively identified because of "considerable natural variability" of the precipitation patterns in the region.

Ocean Circulation Current Likely to Decrease, Unlikely to Collapse
In case you've forgotten parts of An Inconvenient Truth, Atlantic Meridional Overturning Circulation is the feature of the ocean which moves warm, salty water northward in the the upper layers of the Atlantic Ocean and colder water southward in deeper parts of the Ocean.

The USGS concludes that it's very likely that we will witness a 25-30% decrease in strength of this circulation, but it is very unlikely that the AMOC will become severely weakened of collapse by the end of the 21st century, or collapse because of global warming beyond that time period.

Methane Release Will Accelerate Climate Change, Abrupt Release Very Unlikely
In regards to abrupt release of methane into the atmosphere due to global warming, the report concludes that this appears to be very unlikely, but it is also very likely that methane emissions will increase and that this will accelerate global climate change. A doubling of methane emissions in northern high latitudes "could be realized fairly easily."

Read the full report: Abrupt Climate Change
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