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The famous 1.5 ºC figure, widely quoted as the desired ‘maximum’ for planetary warming, stems from the. This treaty declared the goal of keeping the global average temperature well below 2 ºC above pre-industrial levels, with a preferred limit of 1.5 ºC. The 2018 IPCC report on 1.5 ºC of warming notes that effects of reaching this threshold could include: extreme hot days in mid-latitudes that are 3 ºC warmer than in pre-industrial times; sea-level rise of up to three-quarters of a metre by 2100; the loss of more than half of the viable habitat for 8% of plants and 4% of vertebrates; and a decrease in annual global fisheries catches of 1.5 million tonnes.
More important than when Earth will hit 1.5 ºC of warming is what amount of warming the planet will peak at, and when that will happen. “With every tenth of a degree above 2 ºC, you’re looking at more-sustained, more-systemic impacts,” says Solecki.2021 projections of global temperature