What would different levels of global warming look like?

THE PARIS agreement, negotiated at a United Nations summit in 2015, committed its 194 signatory countries (plus the European Union) to try and keep the world’s average temperature to “well below” 2°C above pre-industrial levels, and if possible 1.5°C. The world is already perilously close to that target. In recent years, the average global temperature has regularly been at least 1°C higher than those recorded at the end of the 19th century; in 2020, it was 1.2°C more. The World Meteorological Organisation, a UN agency, predicts that there is “at least a one in five chance of it temporarily exceeding 1.5°C by 2024”. Most of that warming has occurred since 1975, at a rate of about 0.15-0.2°C per decade. Accumulating greenhouse gases in the atmosphere make further warming inevitable. But what difference will a few tenths of a degree make?

1.5°C
The world is already experiencing increasingly erratic weather, including stronger storms and more unpredictable and extreme rainfall patterns, leading to deluges in some places and droughts in others. Even if global average temperature increases are stabilised at 1.5°C, that will still get worse. The annual probability of a heatwave—defined as four days with maximum temperatures above the 99th percentile of a normal warm season—in any given part of the world would rise from 5% to 28%. Sea levels would rise 40-80cm, swelled by melting glaciers, the breakdown of Arctic ice and the expanded volume of warmer oceans. That is more than enough to drown low-lying island nations such as the Maldives. Destructive wildfires like those seen in Australia and on America’s west coast in recent years will also become more frequent.