Ice cover in the Arctic Ocean reached its second-lowest level on record, and ice melt in Antarctica is on track to raise global sea levels 2.5 metres over the very long term, according to two separate studies released in the second half of September.

In the Arctic, “the extent of ice-covered ocean at the North Pole and extending further south to Alaska, Canada, Greenland, and Russia reached its summertime low of 1.4 million square miles (3.7 million square kilometers),” The Associated Press reported, quoting data from the U.S. National Snow and Ice Data Center (NSIDC) . In Antarctica, “melting is likely to take place over a long period, beyond the end of this century, but is almost certain to be irreversible, because of the way in which the ice cap is likely to melt,” The Guardian wrote, citing a modelling study published in the journal Nature.

At the northern pole, last spring’s Siberian heat wave combined with natural phenomena and fossil fuel burning to produce the second-lowest ice extent since the Boulder, Colorado-based NSIDC began keeping track in 1979. AP says temperatures in Siberia were 8.0 to 10°C/14 to 18°F above normal for much of the year.

“Absolutely we’re seeing climate change at work because the warm summers become warmer and the cold winters aren’t as cold as they were,” said Director Mark Serreze.

“What happens in the Arctic, as we say, doesn’t stay in the Arctic,” agreed Pennsylvania State University climate scientist Michael Mann. “We see the impact of Arctic warming in the form of unprecedented heat waves, floods, droughts, wildfire that we are now contending with here in the U.S. and around the rest of the world.”

In Antarctica, “even if temperatures were to fall again after rising by 2.0°C (3.6°F), the temperature limit set out in the Paris Agreement, the ice would not regrow to its initial state, because of self-reinforcing mechanisms that destabilize the ice,” The Guardian explained.

“The more we learn about Antarctica, the direr the predictions become,” said study co-author Anders Levermann, a climate scientist at the Potsdam Institute for Climate Impact Research. “We get enormous sea level rise [from Antarctic melting] even if we keep to the Paris Agreement, and catastrophic amounts if we don’t.”

Either way, after determining the future form of an ice sheet that had remained roughly the same for an estimated 34 million years, “we will be renowned in future as the people who flooded New York City,” Levermann told The Guardian.

“This study provides compelling evidence that even moderate climate warming has incredibly serious consequences for humanity, and those consequences grow exponentially as the temperature rises,” agreed University of Bristol glaciologist Jonathan Bamber. “The committed sea level rise from Antarctica even at 2.0°C represents an existential threat to entire nation states. We’re looking at removing nations from a map of the world because they no longer exist.”

The Clean Arctic Alliance responded to the NSIDC release, and to earlier reports of Greenland’s ice sheet losing a million tonnes of ice per day, by urging “immediate and collective action” to set a trajectory for a 1.5°C ceiling on average global warming—beginning with a 50% reduction in greenhouse gas emissions by 2030. The 20-member Alliance “is campaigning for a robust and effective ban on the use and carriage of heavy fuel oil by shipping in the Arctic, while advocating for shipping to decrease its climate impact, particularly through reductions in black carbon emissions,” the group said in a release.

“The message is clear: 2.0°C means a completely unacceptable risk of loss and damage to human society, from cryosphere dynamics alone,” said Pam Pearson, founder and director of the International Climate Cryosphere Initiative. “We must aim for 1.5°C, and to be frank, to the extent possible plan for a return to 1.0°C as soon as possible, because of the way the cryosphere will respond even at the long-term 1.5°C level, through negative emissions measures. This is an issue of generational justice, and the legacy we leave behind.”