The oceans have heated up at a rate not seen in at least 11,000 years. Since 1970, the Earth’s temperature has raced upwards faster than in any comparable period. The last time it was hotter than now was at least 125,000 years ago, while the atmosphere has more heat-trapping carbon dioxide in it than any time in the past two million years, perhaps more. Through the burning of fossil fuels, we have now unmoored ourselves from our past, as if we have transplanted ourselves onto another planet. Until now, human civilization has operated within a narrow, stable band of temperature. Note: The IPCC scenarios used for best-case, intermediate and worst-case scenarios are SSP1-2.6, SSP2-4.5 and SSP5-8.5. Source: IPCC, 2021: Summary for Policymakers. Cranking up the temperature of the entire globe this much within little more than a century is, in fact, extraordinary, with the oceans alone absorbing the heat equivalent of five Hiroshima atomic bombs dropping into the water every second. The world has already heated up by around 1.2C, on average, since the preindustrial era, pushing humanity beyond almost all historical boundaries. “We have built a civilization based on a world that doesn’t exist anymore,” as Katharine Hayhoe, a climate scientist at Texas Tech University and chief scientist at the Nature Conservancy, puts it. But the single digit numbers obscure huge ramifications at stake. These temperature thresholds will again be the focus of upcoming UN climate talks at the COP26 summit in Scotland as countries variously dawdle or scramble to avert climate catastrophe. The enormous, unprecedented pain and turmoil caused by the climate crisis is often discussed alongside what can seem like surprisingly small temperature increases – 1.5C or 2C hotter than it was in the era just before the car replaced the horse and cart. By Oliver Milman, Andrew Witherspoon, Rita Liu, and Alvin Chang
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