Temporarily exceeding the 1.5°C warming limit set by the Paris Agreement could cause lasting damage to glaciers, ice sheets, frozen ground and polar oceans, according to a new report coordinated by the International Cryosphere Climate Initiative (ICCI) and the UN Environment Programme. The report was released on Monday and draws on contributions from more than 80 scientists specialising in polar and mountain regions.
The report examines “overshoot”: a scenario in which global temperatures rise above 1.5°C before later falling below that threshold. It says the duration and intensity of the overshoot will shape the scale of the damage. Some changes to ice and frozen ground could continue for centuries or even millennia after temperatures decline.
The Greenland and Antarctic ice sheets are among the main concerns. The report says both are already losing ice at roughly six times the rate recorded in the 1990s. As land-based ice melts into the ocean, sea levels rise, increasing risks for coastal communities and cities. Some future rise is already expected because of the instability and sustained retreat of polar ice sheets; over coming centuries, the increase could reach several metres. In some scenarios, sea levels could rise by several centimetres a year.
Returning to temperatures below 1.5°C would slow the process, the researchers say, but would not automatically restore lost ice. The report also argues that staying below 1.5°C may not be enough to preserve the largest ice sheets over the long term, and that warming closer to 1°C or lower would be more protective.
The risks extend beyond melting ice. Warming and acidification in polar oceans could cause lasting changes to marine ecosystems and major ocean currents that help regulate the global climate. Thawing permafrost could also release greenhouse gases stored in the ground, adding to global warming.
The report notes that rising seas could affect Brazil as well as polar regions, increasing coastal exposure to flooding and beach erosion, damaging infrastructure, and allowing saltwater to enter aquifers and agricultural land. Brazil’s National Climate Change Adaptation Plan identifies sea-level rise as a risk to the country’s coastal zone.
To limit the scale and duration of any overshoot, the report’s authors call for faster greenhouse-gas cuts. They recommend reducing emissions by at least 5% a year from now and reaching net-zero emissions by mid-century, alongside a gradual shift away from fossil fuels and increased use of renewable energy. The report says some losses are already unavoidable, but faster reductions in warming could slow glacier melt and permafrost thaw, and under certain conditions allow partial recovery of ice and snow.
Sources: Olhar Digital.