Nine potentially nasty global warming surprises
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Massive global warming report includes chapter on 'potential surprises'
A draft of an upcoming National Climate Assessment report contained an entire chapter on how global warming could have surprising ramifications for humanity.
The full report, more than 500 pages, was posted online in January but not widely noticed until the New York Times published an article about its existence.
Scientists who worked on the Congressionally mandated report told the Times they were worried members of the administration of President Donald Trump, who has shown hostility to climate research, would ignore or downplay the findings.
It’s part of a series of reports to update policymakers on “the impacts of climate change on the United States.”
But even though people have long known the unprecedented rate of global warming since the early 20th century is largely due to the release of heat trapping carbon into the atmosphere by burning fossil fuels, the report also says there are still unpredictable elements to climate change that might contain nasty surprises.
The 15th and final chapter of the U.S. Global Change Research Program Climate Science Special Report is ominously titled: “Potential Surprises: Compound Extremes and Tipping Elements.”
The chapter splits the potential global warming surprises into two categories, compound extremes and tipping points.
Compound extremes are extreme events, such as drought and heatwaves or wildfires followed by heavy rain, that combine to cause even greater disasters.
Tipping points, or critical thresholds, are points at which climate cycles shift from one state to another.
“Humanity is conducting an unprecedented experiment with the Earth system through large scale combustion of fossil fuels and widespread deforestation and the resulting release of carbon dioxide into the atmosphere,” the report states. “Therefore, there is significant potential for our planetary experiment to result in unanticipated surprises and a broad consensus that the further and faster the Earth system is pushed towards warming, the greater the risk of such surprises.”
Here are nine ways the draft report says global warming surprises may unfold.
“One example would be simultaneous drought events in different agricultural regions across the country, or even around the world, that challenge the ability of human systems to provide adequate affordable food,” the report states.
Unprecedented combination of extreme weather events
Unfortunately-spaced droughts aren’t the only potential calamity more likely on a warmer planet.
There’s also the possibility changes to the ocean could combine with extreme weather to make flooding worse.
“The second way in which compound events could surprise would be the emergence of new types of compound events not observed in the historical record or predicted by model simulations,” the report states.
The 2017 Atlantic hurricane season begins June 1 and runs through Nov. 30.
It cites Hurricane Sandy, the second-costliest hurricane in U.S. history, in 2012 as an example.
The report says sea level rise, anomalously high ocean temperatures and high tides combined to strengthen the storm and the storm surge.
At the same time a blocking ridge in the atmosphere over Greenland, which might have been strengthened by surface melt on land and reduced summer sea ice, directed the storm inland to, “an exceptionally high-exposure location.”
Weakened or collapsed Atlantic Ocean circulation
The report cites the Atlantic Meridional Overturning Circulation, a major component of global ocean currents, as a probable tipping point.
The AMOC is driven by the sinking of cold, dense water near Greenland. It’s expected to weaken or possibly collapse due to freshwater input from increased precipitation and runoff from glaciers and the Greenland Ice Sheet.
A weakened AMOC could accelerate sea level rise on the northeastern coast of the U.S. It could also contribute to regional cooling while simultaneously slowing the rate at which the ocean absorbs carbon which would accelerate overall global warming.
The changes would be in addition to the sea level and temperature changes that are already expected.
More frequent strong El Nino cycles
There could also be tipping point changes in the Pacific Ocean related to El Nino and La Nina cycles.
“Climate model experiments suggest warming will reduce the threshold needed to trigger extremely strong El Nino and La Nina events … such a shift would negatively impact many regions and sectors across the United States,” the report states.
Drastic sea ice declines or sea ice disappearance
The report says Arctic sea ice is already disappearing more quickly than anticipated and total summer sea ice loss could change the rate at which heat transfers between the ocean and the atmosphere. The rate of ice loss could also quicken.
Carbon releases from thawing permafrost
The thawing of Arctic permafrost could lead to another tipping point. Permafrost is estimated to contain as many as 1,600 gigatons of carbon. As much as 15 percent could be released into the atmosphere this century, the report states. Further, related decomposition could accelerate carbon release.
Such releases have “the potential to significantly amplify both local and global warming … and drive continued warming even if human-caused emissions stopped altogether,” the report states.
Undersea methane releases
Yet another possible tipping point lies under the sea in the form of methane. There are as many as 3,000 gigatons of carbon in methane hydrates currently frozen in undersea sediment.
Warming water could lead to the release of the methane into the water column and atmosphere, according to the report.
Boreal forest encroachment on tundra
Another tipping point near the top of the planet could come in the form of Alaska’s boreal forests.
The report says the southern Alaskan forests could expand northward in response to warming. Because the forests are darker than the tundra they would replace the expansion would amplify regional warming which would accelerate further boreal expansion.
Climate models that underestimate warming
In addition to surprises that could be baked into the Earth’s climate system’s there could also be surprises in the computer models aimed at predicting the impacts of global warming, particularly in polar regions.
“For this reason, future changes outside the range projected by climate models cannot be ruled out,” the report states. “And climate models are more likely to underestimate than to overestimate the amount of long-term future change.”