After reading about mudskippers yesterday, I eventually connected them with a bit of information I’d forgotten. In the time that mangrove forests and mudskippers were beginning to evolve on the western shores of the Tethys Ocean 50 million years ago, the earth went through a climate catastrophe. Geological eras have names that I find fascinating. This was the beginning of the Eocene epoch, the name means the dawn of modern times. If you want to be more specific, you might call it the Ypresian age, a 8 million year blink of time starting 56 million years ago. What I remembered was that in the Ypresian age the earth went through a heating event that we call the Paleocene-Eocene Thermal maximum (PETM). Temperatures across the earth were between 5 and 8 degress Celsius higher than it is today.
At this time the continents had not yet reached where they are today, as you can see in the map above, but they are not completely unrecognizable. The deep oceans saw a tremendous extinction; between a third and a half of ocean species died out. The oceans became acidified and hot. Their levels rose, water saturated the air. The poles warmed more than the rest of the world. As a result, the Antartic was forested and ice free, and tropical rain forests covered southern Germany. Canada, as far north as what is today Baffin Bay, had swampy conifer forests regularly ravaged by forest fires. The part of India which is now the Thar desert seemed to have had extreme rains and weathering during that time, whereas northern Spain was a parched desert. It is hard to prevent a large body from heating up, so mammals became smaller. This may have had many consequences, but one that has been followed up is that it encouraged a rapid evolution in the ancestors of today’s horses.
Although the map of this world looks almost the same as ours, this hot and rain-drenched world is not suited for agriculture. Estimates of our carbon future showed that in “business as usual” scenario we will be there by the end of the century: in the time of the grandchildren of the millennials. There is a reason that projections stop at the year 2100: no climate simulation remained believable beyond that. Very recently though, a climate model was able to reproduce the PETM using reliable estimates of the amount of CO2 then present in the atmosphere, by following the small-scale dynamics of clouds more accurately. This simulation seems to say that the future temperature rise could be more extreme than had been predicted. We live in unsettled times.