Global Heating Will Hit At Least 1.8C, UN Warns, and There Are 'No Good Outcomes'

An anonymous reader quotes a report from The Guardian: Global heating will reach at least 1.8C under even the most optimistic future, well beyond the Paris agreement goal of 1.5C, according to a UN report that warns every fraction of temperature rise intensifies destructive extreme weather, glacier melt, ecosystem loss, and island and coastal city submersion.

The report by the Nairobi-based UN Environment Program confirmed overshooting the 1.5C goal inscribed in the landmark Paris agreement of 2015 was now "unavoidable" and, despite some progress in addressing the human-caused climate crisis driven by burning fossil fuels, likely in the next few years. It said: "There are no good outcomes above 1.5C."

Heating of up to 3C above preindustrial levels could lead to glaciers losing more than a quarter of their mass by 2100, raising sea levels by up to 13cm. Global food production could decline by up to 14% by 2050 if there are not effective strategies to adapt. Human health, water supplies, nature, cities, infrastructure and economies could all be severely damaged.

Some losses would be irreversible. Many communities may have to relocate or change their livelihoods. The report said the best hope for humanity to limit damage was to adopt an "overshoot, peak and decline" pathway that required immediate and sustained greenhouse gas emissions cuts combined with steps to remove carbon dioxide from the atmosphere.

It described the goal of net zero emissions -- increasingly politically contentious in some countries -- as "an essential milestone that cannot be skipped" and stressed carbon dioxide removal through steps such as establishing vast new forests must occur alongside, not as an alternative to, deep cuts in fossil pollution.

Crucially, the authors of the report, titled Limiting Overshoot, said the average global temperature could be returned to 1.5C this century only if heating stayed below about 1.8C. They warned nature's capacity to store carbon was uncertain and would shrink the more the planet heats. [...] The report's authors cited earlier work that found limiting heating to about 1.8C required global emissions to be halved by 2035.

They said existing national policies were projected to lead to at least 2.3C heating, but it would still be possible to limit stay below 2C if countries delivered on net zero emissions commitments by mid-century.