The difference between the Paris agreement’s 2.0°C top-line target for average global warming and its more ambitious 1.5°C goal could have a massive impact on the frequency of ice-free Arctic summers by the end of the century, according to two new studies in the journal Nature Climate Change.
“At a maximum global average warming of 2.0°C above the norm for most of human history, the Arctic could become technically ice-free once every three to five years,” Climate News Network reports. “Reduce carbon dioxide emissions even further, take greater steps to conserve forests, and keep the global temperature at the 1.5°C maximum rise, and the chances are that the Arctic seaways will open only about one summer in 40 years.”
Even so, “such dramatic loss of sea ice could drive further increases in warming and result in habitat loss for a wide range of species, including polar bears, seals, and walruses,” Carbon Brief notes.
The research teams, one from Canada and the other from the U.S., used two different simulation models to reach the same conclusion on the difference between 2.0 and 1.5°C—and found that at 3.0°C, permanent ice-free summers would be likely.
“I didn’t expect to find that half a degree Celsius would make a big difference, but it really does,” said University of Colorado at Boulder researcher Alexandra Jahn. “At 1.5°C, half the time we stay within our current summer sea ice regime, whereas if we reach two degrees of warming, the summer sea ice will always be below what we have experienced in recent decades.”
Climate News Network and Carbon Brief both explain that glaciologists would consider the Arctic ice-free with sea ice extent of less than a million square kilometres. “Since the satellite record began in 1979, summer sea ice cover has fallen by around 13% per decade,” Carbon Brief states, “with rising temperatures playing a large role in the decline.”
Jahn said polar seas might bounce back faster than other ecosystems that would more likely see permanent impacts from ice loss. “The good news is that the sea has a quick response time and could theoretically recover if we brought down global temperatures at any point in the future.”
But “both studies find that, even if warming is limited to 1.5°C, the risk of an ice-free Arctic is likely to grow larger over time,” Carbon Brief cautions. This is because in addition to the long-term downward trend, there is also year-to-year natural variability in Arctic sea ice cover,” adds reporter Daisy Dunne, citing University of Exeter climate scientist James Screen, who published an article to accompany the new research.