Temporarily exceeding 1.5C of global warming could cause irreversible ice loss and speed up sea-level rise, according to a new report produced by the UN Environment Programme (UNEP) and the International Cryosphere Climate Initiative (ICCI). The document brings together more than 80 scientists and examines the so-called overshoot, a period in which the planet's average temperature passes 1.5C and then falls again.
The researchers say that even if warming is later reduced, some impacts on glaciers, ice sheets, permafrost and polar oceans could continue for decades or centuries. The large ice sheets of Greenland and Antarctica are already losing mass about six times faster than in the 1990s, according to the report. The greater and longer the overshoot above 1.5C, the larger the likely contribution to sea-level rise.
The report warns that some instabilities in ice sheets could, over the coming centuries, raise sea levels by several meters and produce periods of advance of up to a few centimeters per year. Even in scenarios where the temperature returns to 1.5C, part of the ice loss would continue. The authors say a level considered safer for the large ice sheets would be closer to 1C of warming, or even below that.
Impacts also extend to the oceans. Warming and acidification of polar waters, as well as changes in major ocean currents, could persist for centuries even after global temperatures eventually decline.
For Brazil, one of the main consequences is sea-level rise, which increases the risk of coastal flooding, beach erosion and saltwater intrusion into aquifers and agricultural areas.
The authors advocate rapid cuts in greenhouse gas emissions to keep any overshoot of 1.5C as short and small as possible. According to the report, reducing emissions by at least 5% per year and reaching net zero emissions by mid-century could still limit some losses, although some impacts can no longer be completely reversed.
Sources: G1.