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<\/div>Illustration of the end-Permian extinction event, when extreme temperatures may have killed off forests<\/p>\n
RICHARD JONES\/SCIENCE PHOTO LIBRARY<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
The Great Dying at the end of the Permian Period 250 million years ago may have been amplified by El Ni\u00f1o events<\/a> far stronger and longer lasting than any today.<\/p>\n These mega El Ni\u00f1os caused wild swings in the climate that killed off forests and many land animals, says Alexander Farnsworth<\/a> at the University of Bristol in the UK.<\/p>\n They also triggered feedback processes that helped make this mass extinction as bad as it was, he says. \u201cThere are knock-on effects of this sort of El Ni\u00f1o event becoming stronger and lasting longer.\u201d<\/p>\n Around 90 per cent of all species alive at the time may have gone extinct during the end-Permian extinction, making it the worst ever mass extinction<\/a>. It is widely thought that it was triggered by massive volcanic eruptions in what is now Siberia<\/a>.<\/p>\n These eruptions released huge quantities of carbon dioxide \u2013 possibly by heating rocks full of fossil carbon<\/a> \u2013 that led to extreme global warming. The ocean became stagnant and low in oxygen<\/a>, killing off marine creatures.<\/p>\n But this doesn\u2019t explain everything. In particular, land species started going extinct tens of thousands of years earlier than those in the sea.<\/p>\n <\/p>\n Many ideas have been put forward to explain this<\/a>, from volcanic winters<\/a> to the loss of the ozone layer. The idea that extreme El Ni\u00f1os might be involved emerged from studies of past ocean temperatures, based on oxygen isotypes in fossils, led by Yadong Sun<\/a> at the China University of Geosciences in Wuhan.<\/p>\n Now, Farnsworth and his colleagues have run computer models to explore what might have happened at end of the Permian that could explain Sun\u2019s findings.<\/p>\n Today, El Ni\u00f1o occurs when warm water in the western Pacific spreads eastwards across the surface of the ocean. This creates an area of abnormally warm water that heats the atmosphere and affects weather across the planet.\u00a0<\/strong><\/a><\/p>\n Before the Permian extinction began, the researchers found, El Ni\u00f1os were probably of a similar intensity and duration as today. That is, the anomalously warm water was about 0.5\u00b0C (0.9\u00b0F) hotter than average and the events lasted for a few months.<\/p>\n These events, however, were happening in a massive ocean called Panthalassa<\/a>, which was 30 per cent wider at the equator than the Pacific Ocean is today. This means the area of anomalously warm water during El Ni\u00f1os was much larger than today, and thus had a bigger planetary impact.<\/p>\n As CO2 levels rose at the end of the Permian, these El Ni\u00f1o events got stronger and lasted longer, the team\u2019s models suggest. They caused extreme swings in the weather on land that killed off forests, which stopped soaking up CO2 and started releasing it, leading to more warming and even more extreme El Ni\u00f1os.<\/p>\n In the sea, the temperature variations would have been less severe, and marine animals can more easily migrate to avoid them. This explains why marine extinctions happened later, when global warming got more intense. \u201cThe killer extreme global warming that was the cause of marine extinction was worse because of these El Ni\u00f1os taking away the carbon sink,\u201d says Farnsworth.<\/p>\n By the peak of the extinction, the temperature anomaly during El Ni\u00f1os was up to 4\u00b0C (7.2\u00b0F), with each event lasting more than a decade, he says.<\/p>\n It isn\u2019t clear if something similar will happen in the future. Computer models vary in their forecasts of how El Ni\u00f1os will change as the planet warms, says Farnsworth. But they are already having a bigger impact because they are happening in a warmer world<\/a>.<\/p>\n \u201cThe El Ni\u00f1o we just had was helping set record temperatures everywhere and leading to a huge amount of forest fires,\u201d he says. \u201cAnd the thing that disturbs me most is tentative signs during this El Ni\u00f1o of dieback in the Amazon.\u201d<\/p>\n The study shows that under specific climate conditions, El Ni\u00f1o events can cause extinctions, says Pedro DiNezio<\/a> at the University of Colorado, Boulder. But these mega El Ni\u00f1os couldn\u2019t occur today because the Pacific is smaller than Panthalassa, they say.<\/p>\n \u201cThese results are very exciting to understand the past, not so much the near future. To answer what El Ni\u00f1o will do, we need to look at intervals in the past with similar continental configurations as today,\u201d says DiNezio.<\/p>\n \u201cI think it\u2019s a compelling study,\u201d says Phil Jardine<\/a> at the University of M\u00fcnster in Germany, who found the first direct evidence for the loss of the ozone layer during the Permian extinction<\/a>.<\/p>\n \u201cI don\u2019t think that this and other extinction drivers, including ozone degradation, are mutually exclusive,\u201d he says. \u201cThe deadly thing about the end-Permian mass extinction seems to be that a lot of things were happening at once, and interacting with each other as they cascaded through the Earth system.\u201d<\/p>\n Topics:<\/p>\n<\/section><\/div>\n