At the landmark Paris climate agreement, nearly every country in the world pledged to a goal to limit warming to well below 2° Celsius (3.6° Fahrenheit) above preindustrial levels by 2100, and work toward a more ambitious goal to limit warming to 1.5°C (2.7°F). The hope is that such a limit will help Earth avoid the most catastrophic effects of climate change.
However, a recent review suggests that even the more ambitious ceiling of 1.5°C may be too warm for the planet’s polar ice sheets and trigger massive sea level rise.
Researchers looked at paleoclimate data to see what the sea level was when Earth in the past was at a temperature comparable to the present. They combined that information with modeling data and more recent observations to then assess how much ice loss can be expected with 1.5°C of warming.
The world is currently about 1.2°C (2.2°F) warmer than it was before humans began emitting massive amounts of warming fossil fuels, or pre-1900. Even at the current warming, “in the last few years, we’ve just seen some really dramatic changes in the Greenland ice sheet and the West Antarctica ice sheet in particular,” Chris Stokes, the study’s lead author, from Durham University, U.K., told Mongabay in a video call. He added researchers were surprised by the amount of melting they’ve observed already.
The hope has been that 1.5°C of warming is below the threshold for massive glacial melting. So, “we wanted to see what the impact of 1.5 degrees of warming would be on those ice sheets,” Stokes said. They found that it’s still too warm for polar ice sheets in Greenland and Antarctica.
Together, the Greenland and Antarctic ice sheets hold enough water to raise global sea levels by tens of meters, Stokes said. And even if we do limit warming to 1.5°C, he added, we should expect “a few meters, best-case scenario, of sea level rise over the next couple of centuries.”
“These are large numbers,” Harry Zekollari, a glaciologist at the University of Brussels, Belgium, who wasn’t involved with this study, told Mongabay by email. He added the review study is “a very strong piece combining different lines of evidence.”
Zekollari recently published a related study in Science, which found that nearly twice as much glacial mass will be lost if the climate warms by 2.7°C (4.9°F) by 2100, a likely scenario, according to several climate model forecasts.
The 1.5°C goal is still important for many other Earth systems, so “the message is certainly not to give up hope or not to aim for that target,” Stokes said. “But if you’re interested in sea level rise, or you’re a country with a low-lying coastline, or with low-lying inhabitants close to the coastline, then this problem is not going to go away.”
Banner image of glacial melting in the Himalayas by Sharada Prasad via Wikimedia Common (CC BY 2.0).
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