It’s not just about sea level rise or ocean acidification. It’s the heat too, which is deadly in parts of the US already.
New York magazine writes, “. . . .
“. . . the climate window that has allowed for human life is very narrow, even by the standards of planetary history. At 11 or 12 degrees of warming, more than half the world’s population, as distributed today, would die of direct heat. Things almost certainly won’t get that hot this century, though models of unabated emissions do bring us that far eventually. This century, and especially in the tropics, the pain points will pinch much more quickly even than an increase of seven degrees. . . . .
Actually, we’re about there already. Since 1980, the planet has experienced a 50-fold increase in the number of places experiencing dangerous or extreme heat; a bigger increase is to come. The five warmest summers in Europe since 1500 have all occurred since 2002, and soon, the IPCC warns, simply being outdoors that time of year will be unhealthy for much of the globe. Even if we meet the Paris goals of two degrees warming, cities like Karachi and Kolkata will become close to uninhabitable, annually encountering deadly heat waves like those that crippled them in 2015. At four degrees, the deadly European heat wave of 2003, which killed as many as 2,000 people a day, will be a normal summer. At six, according to an assessment focused only on effects within the U.S. from the National Oceanic and Atmospheric Administration, summer labor of any kind would become impossible in the lower Mississippi Valley, and everybody in the country east of the Rockies would be under more heat stress than anyone, anywhere, in the world today. As Joseph Romm has put it in his authoritative primer Climate Change: What Everyone Needs to Know, heat stress in New York City would exceed that of present-day Bahrain, one of the planet’s hottest spots, and the temperature in Bahrain “would induce hyperthermia in even sleeping humans.” The high-end IPCC estimate, remember, is two degrees warmer still. By the end of the century, the World Bank has estimated, the coolest months in tropical South America, Africa, and the Pacific are likely to be warmer than the warmest months at the end of the 20th century. Air-conditioning can help but will ultimately only add to the carbon problem; plus, the climate-controlled malls of the Arab emirates aside, it is not remotely plausible to wholesale air-condition all the hottest parts of the world, many of them also the poorest. And indeed, the crisis will be most dramatic across the Middle East and Persian Gulf, where in 2015 the heat index registered temperatures as high as 163 degrees Fahrenheit. As soon as several decades from now, the hajj will become physically impossible for the 2 million Muslims who make the pilgrimage each year.”
And it’s about more. At some point before 2100, the only planet we have to live on will be too hot to support human life in many if not most parts of ththe Earth. Animals and crops will also not survive.