A new study in the journal Science finds that even the most aggressive goals of reducing greenhouse gas emissions aren’t sufficient to avoid several major climate change tipping points, in which rising temperatures cause irreversible damages that in turn cause more global warming.
One of the most worrisome risks of climate change, for example, is that permafrost — a layer of frozen soil in the polar regions — will continue to thaw, releasing planet-warming gases such as carbon dioxide and methane that are currently embedded in the soil. Arctic permafrost alone contains roughly 51 times as much carbon as the entirety of 2019’s global emissions, according to NASA, and if it thaws would speed up global warming at an alarming rate. The last two global climate change agreements brokered by the United Nations have set an aspirational goal of limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels, with a fallback goal of 2°C (3.6°F), in order to stave off that kind of catastrophe.
But the new study finds that the permafrost may permanently thaw even if warming stays between the current 1.1°C of warming and 1.5°C, and becomes “likely” if warming falls between 1.5°C and 2°C.
In addition to thawing permafrost, other potential risks include “collapse of the Greenland and West Antarctic ice sheets” and “die-off of low-latitude coral reefs.” If the Greenland ice sheet melts entirely, it could result in 20 feet of sea level rise. Last year a study by the Potsdam Institute for Climate Impact Research in Germany found that 3 to 6 feet of sea level rise from partial melting of the Greenland ice sheet is already likely to occur, though at its current rate it would take centuries. A full-scale collapse of the ice sheet could have a wide array of dramatic consequences, including the disruption of the Atlantic Meridional Overturning Circulation current, a warm band of water that flows to the northeast across the Atlantic Ocean, which would cause much colder winter temperatures in Europe.
Coral reefs — underwater structures in the ocean made from the skeletons of marine invertebrates called coral — create an ecosystem that supports robust plant and animal life, and the mass death of coral reefs would deprive marine life of their habitat, destroying ocean biodiversity.
Another emerging tipping point is the dieback of the Amazon rainforest. The Amazon covers more than 2 million square miles and acts as an enormous carbon sink that helps keep temperature rise in check. Its destruction could release the equivalent of several years’ worth of global carbon emissions. “Dieback” refers to the risk that after logging and wildfires, the Amazon will no longer grow back as rainforest due to warmer temperatures increasing water evaporation and drying out vegetation. A study published in the journal Nature Climate Change in March found that the Amazon may be reaching a tipping point in which dieback begins.
“Since I first assessed climate tipping points in 2008 the list has grown and our assessment of the risk they pose has increased dramatically,” Tim Lenton, a professor of climate change at the University of Exeter in England, who co-authored the new study in Science, said in a statement.
“We can see signs of destabilization already in parts of the West Antarctic and Greenland ice sheets, in permafrost regions, the Amazon rainforest, and potentially the Atlantic overturning circulation as well,” the Science study’s lead author, David Armstrong McKay, who is affiliated with the Stockholm Resilience Centre and the University of Exeter, said. “The world is already at risk of some tipping points. As global temperatures rise further, more tipping points become possible.”
The study’s publication was timed to coincide with a three-day conference, beginning Monday, to analyze climate tipping points.
Currently, the world is on a course to blow past 1.5°C of warming. Climate Action Tracker (CAT), an independent scientific analysis, studied the national plans to reduce emissions released at the last U.N. Climate Change Conference, in Glasgow, Scotland, and found the world is on course for between 1.7°C and 2.6°C of warming. (The lower number takes lofty promises of far-off emissions reductions at face value, while the higher number is based on the policies nations have actually adopted.) In May the World Meteorological Organization put the world’s chances of breaching 1.5°C of warming at fifty-fifty.
But now it seems that even stronger action might be needed to avert catastrophic climate change. The Science study’s authors argue that their research on tipping points demonstrates just that.
“The chance of crossing tipping points can be reduced by rapidly cutting greenhouse gas emissions, starting immediately,” McKay said.