Scientists have unearthed information about the unpleasant precedent associated with climate change
During the spread of mammals around the planet, the temperature of the Earth has risen sharply and dangerously - and the planet may face this again.
The beginning of the mammal era was very strange. The planet still departed from the amazing disappearance of its famous superstars, dinosaurs. The newest crater of the Earth was still a smoking system of hydrothermal springs billowing around the Gulf of Mexico. After such an Armageddon, our deafened ancestors quietly agreed on new roles on the planet inherited by chance. And soon life got adapted to the new rhythms - 15-meter boas plied the jungle greenhouses, the birds grew to gigantic proportions, imitating their cousins who had left them, and mammals appeared, relatively similar to the modern ones, which we could recognize with some effort. And within a few million years, freed from the iron heel of the vanished giants, they began to experiment. Early whales plied the Pakistani archipelago on four legs, testing life in the water. The first lemur-like primates jumped from the treetops, and all sorts of ungulates rushed back and forth through the forest.
But the most surprising feature of the early period of mammals was the all-pervasive heat - it was so hot that 50 million years ago crocodiles, palm trees and gray sandy sharks were found behind the Arctic Circle . On the other hand of the blue-green ball, in the waters that are now washing Antarctica, the temperature of the water surface could reach an incredible 30 ºC today, and almost tropical forests grew in Antarctica. In the tropics, there were lifeless zones, too hot for some plants or animals to survive.
This situation prevailed in the ancient atmosphere, 0.1% of which (1000 ppm) was carbon dioxide. If this figure seems familiar - you are right, it is to such a state that humanity must bring the planet to the end of this century. That should bother us a little.
“Throw more CO 2 into the atmosphere — and get a warming boost. This is extremely simple physics, which we thought of as far back as the 19th century, ”says David Naafs, an expert in organic geochemistry from the University of Bristol. “But how precisely [the planet] will be heated by the end of the century, we do not know. Based on our studies of ancient climates, we can say that more than we thought. ”
Last week, Naafs and colleagues released a study in the journal Nature Geoscience, where they reconstructed temperatures on land during this ancient CO 2 high sauna that existed in the Late Paleocene and Early Eocene , in the sultry beginning of the mammalian era. And they dug up unexpectedly burning temperatures.
Scientists need good stones to study the past of the earth, and fortunately for geologists and mineral companies, a huge amount of coal has remained in the jungle and swamps from the early mammalian era. The Powder Valley in the United States, for example, is filled with the Paleocene fossil swamps, which, burning today, make about 10% of the contribution to carbon emissions in the United States. The Naafs team studied examples of low-grade coal, black lignite , or fossil peat. Such coal was found all over the world (everywhere, from open mines in Germany to naked rocks in New Zealand), and the time of its appearance stretched from the late Paleocene to the early Eocene, from 56 to 48 million years ago. Scientists were able to restore the state of the ancient climate, analyzing the temperature-sensitive structureslipids produced by fossil bacteria and archaea that lived in these extinct swamps and are preserved in coal. The team found that in the past, with a high CO 2 content , in ancient Britain, Germany and New Zealand, life tolerated average annual temperatures of 23-29 ºC, which is 10-15 ºC warmer than today.
“These wetlands looked exactly like tropical bogs today, such as the Everglades on Amazon,” says Naafs. “So Europe looked like the Everglades, and such a sudden wave of heat that we are experiencing now [mid-summer 2018] would be perfectly normal. That is, such a climate would be everyday. ”
Today's hot weather, established in Europe, forced the Scandinavians to sunbathe, and drove deer to the beaches, at temperatures reaching 32 ºC within the Arctic Circle. She lit devastating forest fires in Greece and caused an unbearable weekend in Spain and Portugal. But more than 50 million years ago, such weather would be basic for latitudes from 45º to 60º. And in such hot weather, when unprecedented heat would be normal, a wave of unexpected heat would seem inhuman.
“Perhaps a wave of hot weather in Europe would set the weather around 40 ºC for three weeks. We do not know". Such was the life at the end of the Paleocene and the beginning of the Eocene at middle latitudes. But closer to the equator in this global bath, the heat should have been even more brutal, overcoming the limitations of a complex life. To find out how cruel, the team Naafsa analyzed samples of ancient lignite from India, which all the time had to exist in the tropics - this subcontinent is still moving across the Indian Ocean to meet its rendezvous with Asia, which is uplifting the mountains. But, unfortunately, it turned out that the temperature of those samples exceeded the maximum. They were too high to be measured by a newly developed method. Therefore, the question of how hell were the tropics in the early days of our ancestors,
“Some climate models suggest that the tropics were a dead zone with temperatures exceeding 50 ºC, for example, in Africa and South America,” says Naafs. “But we have no data, so we do not know.”
The work of Naafsa fits into a larger general view of the Earth as an almost unrecognizable greenhouse planet in the distant past. Paleontologist Jaelyn Eberle [Jaelyn Eberle] from the University of Colorado recently returned to her office in the town of Boulder from Ellesmere Islandlocated in Canada beyond the Arctic Circle, where she has conducted research since the 1990s. Ellesmere is as far in the north as you can get, so as not to fall off North America and not meet Santa Claus. There, the lifeless highlands rise above the ice-packed fjords, and only lonely reindeer can interlace with the musk oxen under the vast sky of Nunavut . Polar bears are still there, but Eberle was lucky not to meet any of them yet - although there, at the top of the world, the prospect may play a joke with you, and a snow-white polar hare standing on its hind legs may seem threatening at a certain distance.
“You get a gun, you start to worry, and then you look through binoculars - and this is just a rabbit,” says Eberle.
But she climbs north not just to sometimes meet representatives of the polar fauna. Her goal - fauna warmer times. Although there, on the top of the world, trees do not grow, there are hemp trees there. And they are about 50 million years old.
“The fossil forests on Ellesmere are a terrific sight,” Eberle tells of an ecosystem buried in Arctic soil. “As soon as you begin to study them in detail, a surprise arises — wow, this is a jungle.”
Eberle is a paleontologist specializing in vertebrates, and although musk ox can pass by her camp, there are enough different animals to explore in the soil beneath it.
“There are alligators, giant turtles, primates, all that. The huge animals like hippos - coryphodon. Tapirs - that is, we have tapirs here, who lived close enough to the North Pole at the beginning of the Eocene, despite the fact that tapirs do not live at the pole today, ”she laughs.
The presence of these animals indicates a very warm climate. Still, there is a rather big difference between traditional future warming predictions - for example, what the Intergovernmental Panel on Climate Change (IPCC) gives, talking about warming at about 4 ºC by the end of the century while maintaining current emissions and sea level rise a few centimeters - and virtually unrecognizable Earth, buried in the rocks, which appeared at similar rates CO 2 , which unearths Eberly.
One obvious way to eliminate the discrepancy is to note that the changes of the ancient Earth have been going on for hundreds of thousands and millions of years, and the planet will not stop changing at the end of the 21st century. The changes, the beginning of which we are already witnessing, will fully unfold, too, only in the millennia - if we do not take prompt measures to compensate for them. The last time the CO 2 content was equal to the current one at 400 ppm (0.04%) 3 million years ago in the Pliocene, when the sea level was about 25 m higher than today. Obviously, the climate has not reached equilibrium with the world with such a content of CO 2 .
And it will take a long time to wait. In any case, we will definitely not stop at 400 ppm. If we bring the content of CO 2to values of the order of 1000 ppm by the end of the century, warming will not go anywhere, and the Earth will continue to change so long that for people this period will seem like an eternity. And when, finally, the Earth's system comes to equilibrium, it is likely to be a state that cannot be found in the brief evolutionary history of Homo sapiens. What is most unpleasant, climate models, on which we, as a species, depend in matters of predicting our future, for the most part did not cope with the prediction of our sultry past. And although the gap is narrowing, the models approach the truth, even those that are close to reproducing early Eocene greenhouses require an increase in atmospheric CO 2 16 times compared to modern - this goes far beyond simply doubling or tripling CO 2indicated by fossil records.
We are obviously missing something, and Naafs believes that one of the missing ingredients in the models is methane, a gas with a powerful greenhouse effect, which can help close the gap between the world of models and the world of fossils.
“We don’t know anything about methane cycles during these greenhouse periods,” he says. “We know that the warmer it gets, the more methane the bogs emit, but we don’t know anything about methane cycles outside of the ice cores available, and they are only 800,000 years old. We know that tropical swamps pump much more methane into the atmosphere compared to colder swamps. And we know that methane is capable of increasing warming at high latitudes, and this may be the missing feedback. ”
In many aspects, these ancient worlds do not compare with ours. It is necessary to carefully compare two different worlds. The early era of mammals was not the same as today's planet. The continents were located differently, which is why the ocean circulated wrongly, and the boundary conditions 50 million years ago were not at all the same as ours - during all this huge time, a huge amount of changes occurred in tectonics, oceanography and biology. But if artificially pumping a lot of greenhouse gases into the atmosphere, then, according to Naafs, you can recreate many of the wildest aspects of the early mammal age.
“If we burn all the fossil fuels and wait a few centuries, we can return to this state,” he says. - In fact, in all types of paleoclimatic studies it has been demonstrated that a high content of CO2 means very warm climate. And when it gets very warm, it can become very, very warm. ”