Earth underwent rapid global warming 300 million years ago •

A new study published in the journal Proceedings of the National Academy of Sciences studied a period of rapid global warming 300 to 260 million years ago, when Earth’s climate changed from a glacial cooler to a hot, ice-free greenhouse. According to scientists, in the space of around 300,000 years, atmospheric carbon dioxide levels doubled, the oceans became anoxic and biodiversity dropped significantly both on land and in the seas.

Although several other hyperthermic or rapid warming events are known in the history of our planet, this one appears to be one of the fastest. Moreover, it was the first such event identified in a terrestrial icehouse, when the planet had a variety of ice caps and glaciers, comparable to the current situation. Experts say a cooler climate may be more sensitive to changes in atmospheric carbon dioxide levels than warmer conditions, when levels of this gas are already higher.

In this study, the scientists focused on a transition 304 million years ago known as the Kasimovian-Gzhelian, or KGB, boundary. Using multiple proxies, such as carbon isotopes and trace elements from rocks and plant fossils, they estimated that about 9,000 gigatons of carbon were released into Earth’s atmosphere just before the KG boundary.

This period of massive carbon release also led to marine anoxia, or a drop in dissolved oxygen levels in the oceans. Since melting ice caps release fresh water to the surface of the ocean, they create a barrier to deep water circulation and cut off the supply of oxygen, leading to the extinction of many marine species. By measuring uranium isotopes in carbonate rocks in present-day China, scientists were able to get an approximation of how much oxygen was in the ocean when the rocks were deposited. They estimate that 23% of the world’s seabed has become anoxic dead zones, leading to high biodiversity losses.

According to study co-author Isabel Montañez, a paleoclimatologist at University of California, Davis, the effects of carbon release on ocean anoxia were significantly greater than those observed in other studies of rapid warming under “greenhouse” conditions, in which the baseline level of atmospheric carbon dioxide was already higher. raised. “If you increased the CO2 of the same amount in a greenhouse world, there is not much effect, but coolers seem to be much more sensitive to change and marine anoxia,” Professor Montañez said.

The researchers concluded that this massive release of carbon may have been triggered by volcanic eruptions that tore through the carboniferous coal beds and sparked a large number of forest fires. The rapid warming caused by these events may have melted the permafrost, releasing even more organic carbon into the atmosphere.

By Andrei Ionescu, Personal editor

Teresa H. Sadler