The earth is getting especially hot this year, as record after record falls. Seth Borenstein at AP reports that three times this past week, the average temperature of the earth topped anything ever recorded. Thursdays average 17.18 C. (62.9 F.) broke the record yet again.

You dont break all those records without the accumulation of heat-trapping gases in the earths atmosphere, put there by humans burning gasoline in their cars and coal and fossil gas to heat their homes. Weve put so many greenhouse gases up there that they arent letting the heat of the suns rays dissipate back out to space the way they used to, so were stuck with that heat on earth.

This year, another consideration affects the temperatures, which is the El Nio phenomenon. Ordinarily, trade winds blow west from South America toward Asia, whipping up warm ocean waters and driving them toward Asia. But that causes colder waters to come to the surface over time. Im interested in all this as a historian, since the direction of trade winds is important to trade history. Ship captains in the age of sail used to have to know these things and depended on them in their voyages. Weak trade winds could leave you marooned for weeks at a time and be the difference between profit and loss, maybe even life and death.

Every once in a while,NOAA explains,the westerly trade winds weaken, so that the warm waters of the Pacifics surface flow instead back east toward the South American coasts. The Latin American fishermen who noticed this warm water arriving, typically in December, called it Baby Jesus, basically _el Nio de navidad._The flow of warm water toward Latin America pulls down the jet stream to a more southerly route. It can cause hot, dry weather in much of North America, though it increases heat and humidity down along the Gulf Coast.

So these two things are going on this year. We have an el Nio, which is making it hotter than usual in some places. But that el Nio is coming on top of a run-up of 1.1 C (about 2 F.) in the average surface temperature of the earth since the Industrial Revolution.

So we get a lot of broken records. Because it is an el Nio year, the broken records dont actually signal a tipping point or any dramatic departure from the climate scientists models, which work over decades, not over months. The broken temperature records arent meaningless though, since they wouldnt exist without that extra 2 F. of heating from CO2 and methane that humans have spewed into the atmosphere.

Although 17.18 C (63 F.) doesnt sound sweltering, remember that this is the average surface temperature of the entire earth. It would be brought down by Antarctica and the North Pole, by the Himalayan mountains and the surface of frigid seas. For the average to be in the 60s F. it also has to be really, really hot in other places. And it is really, really hot in some places Texas, Mexico, Beijing, parts of the Mediterranean, Nigeria even Canada, of all places. Borenstein quotes Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research in Germany, who says that 63 F. is six degrees hotter than the average for the past 12,000 years.

And he quotes preeminent climate scientist at the University of Pennsylvania, Michael E. Mann, as suggesting that it is the warmest average temperature seen on earth for at least 120,000 years. That was when the great glacial period of 120,000 before present (BP) to 11,500 BP began. For the past 11,500 years weve been in a warmer inter-glacial period, the Holocene, which is why there arent three miles of ice over Manhattan and why the Great Lakes exist, which are filled with the water of retreating glaciers. Civilisation emerged in the warmer but still cool Holocene. The average temperature during the Holocene was more like 57 F. During the glacial period, of course, it was much colder. So you have to get back behind the glacial period to find another time when the average temperature of the earth was this hot, some time in the past more distant than 120,000 BP.

Our species, modern homo sapiens, is only about 160,000 years old, so it is just possible that our kind has never experienced an earth as hot as it is now. Certainly, for most of the time we have been evolving, it has been much cooler than it is today. I would argue that you can tell that we did not evolve under superhot temperatures and high humidity, since we drop dead within six hours when it is113 F with 50 percent humidity. At 122 F and 80 percent humidity we pretty much die on the spot. We cool down by sweating, but at such high humidity that cooling mechanism stops working and we get massive heat stroke. If those conditions, which are beginning to emerge on theIranian coast of the Gulfin the depth of summer. had been routinely encountered early in our evolution, then natural selection would have chosen out people who could survive them and our tolerance would be higher.

We are for the first time entering an epoch in the worlds climate history where we will be irremediably maladapted to significant numbers of places. We can live in very cold places by building fires and appropriating warm fur from animals. In the old days Bedouins crossed Saudi Arabias Empty Quarter desert with camels and water bags. But at 122 F with 80 percent humidity there is no cultural practice that will keep us alive when we venture outside, except maybe space suits. There will be heat-death zones on the surface of the earth that humans will avoid, and these zones will grow up in places where people now live, sohundreds of millionsof us over the next centuries will have to move house. If we can stop farting out billions of tons of carbon dioxide annually, the heat-death zones will be limited in scope, and most of the earth will still be habitable, even if uncomfortably warm.

If we get to zero carbon by 2050, we could get back down to 350 parts per million of CO2 in our atmosphere in a century and a half. The year 2200 sounds science fictiony and as though it is beyond our concern. But my maternal grandfather was born in 1889, and he told me things when I was young about his early education and the routine of memorisation that I still remember. Those are memories from 125 years ago. The past seems much closer than the future, but it is an optical illusion. Many younger peoples great-grandchildren, if they are long-lived, will die only a few decades short of 2200.

It is worthwhile making some sacrifices so that we dont leave our great-great-grandchildren a hellhole as an inheritance.

First published in Informed Comment July 8, 2023

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