By Henry Fountain
© The New York Times Co.
Scientists Wednesday reported another reason the world should sharply rein in global warming: Doing so would likely cut in half the current projected amount of sea level rise from the melting of ice this century.
In a study that averaged results of hundreds of computer simulations from research teams around the world, the scientists said that limiting warming to 1.5 degrees Celsius could reduce sea level rise from melting glaciers and the vast Greenland and Antarctic ice sheets from about 10 inches to about 5 by 2100.
That level of warming, equivalent to 2.7 degrees Fahrenheit, is the stricter of two targets set by the 2015 Paris agreement to combat climate change.
But the world has already warmed about 1.1 degrees Celsius since 1900 and is not on course to meet the 1.5 degree target or even the higher Paris goal of 2 degrees Celsius.
In a second study published in the same journal, Nature, a separate group of scientists looking only at Antarctica found that overshooting those targets and reaching 3 degrees Celsius of warming — which the world is roughly on track to do, given current pledges to cut emissions — could trigger an abrupt increase in the rate of melting around 2060 and drive a rate at the end of the century that would be 10 times faster than today.
Together, the two studies are the latest best forecasts related to one of the most concerning impacts of climate change: rising oceans that will cause more flooding, force costly overhauls to coastal infrastructure and potentially create millions of climate refugees.
The studies are also the latest to starkly illustrate both the benefits to be gained from reducing warming by drastically cutting emissions of carbon dioxide and other heat-trapping gases, and the perils of failing to do so.
“You can conclude from both studies that mitigation and emissions reductions will be important with regard to how much sea level rises,” said Peter U. Clark, a geologist at Oregon State University who researches sea level but was not involved in either study.
Melting of ice currently accounts for about half of sea level rise; almost all of the remainder is a result of expansion of ocean water as it warms. A special report published in 2019 by the United Nations Intergovernmental Panel on Climate Change found that total sea level rise by 2100 could range from about 1 foot to more than 3 feet, depending on how much the world warms.
Modeling how land ice will behave as the temperatures rise is difficult, especially for the thick Greenland and Antarctic ice sheets. These studies show that the models are improving, Clark said, although uncertainties remain.
Those uncertainties are especially large when it comes to Antarctica, which, if it melted completely over many centuries, would raise the oceans by several hundred feet. While the first research team, led by Tamsin Edwards, a climate scientist at King’s College, London, found the potential ice contribution to sea level rise could be cut in half, the researchers also looked at a smaller group of the simulations — those in which Antarctica was more sensitive to warming.
Analyzing those more pessimistic results — but the kind that might be useful to policymakers and others who have to plan for protecting costly ports, power plants or other infrastructure — the researchers found that even if the world succeeded in meeting the stricter Paris goal, the contribution of Antarctic ice to sea level rise could be much higher.
Edwards said that rather than cutting the total ice contribution to sea level rise from 10 inches to 5 by 2100, the more pessimistic findings suggested the contribution could be 16 inches. And even if warming were limited to 1.5 degrees, she said, there was a 5% chance that melting ice would add nearly 2 feet to the oceans.