{"id":6159,"date":"2017-08-31T09:50:44","date_gmt":"2017-08-31T08:50:44","guid":{"rendered":"https:\/\/ounews.co\/?p=6159"},"modified":"2017-08-31T09:50:44","modified_gmt":"2017-08-31T08:50:44","slug":"volcanic-emissions-caused-the-warmest-period-in-past-56m-years-new-study","status":"publish","type":"post","link":"https:\/\/www.open.ac.uk\/blogs\/news\/science-mct\/science-environment\/volcanic-emissions-caused-the-warmest-period-in-past-56m-years-new-study\/","title":{"rendered":"Volcanic emissions caused the warmest period in past 56m years \u2013 new study"},"content":{"rendered":"

To predict what type of Earth lies ahead of us, we scientists usually turn to complex computer simulations. But how can we test whether these models are remotely accurate? Perhaps the best solution is to turn to instances in the geological past when Earth\u2019s climate experienced similarly rapid warming. One such event is the Palaeocene-Eocene Thermal Maximum<\/a> (PETM) that occurred 56m years ago.<\/p>\n

In our latest research<\/a>, we have identified the cause of this well-known warm period. Its links to present day climate change are clear.<\/p>\n

Just prior to the PETM, Earth looked very different than it does today. The polar regions were devoid of ice sheets, with temperate or even subtropical forests along the coastlines of Antarctica<\/a>, and Arctic Canada resembling the swamplands of modern Florida. The deep oceans were about 10\u00b0C warmer than today, and warm climate zones were all shifted polewards.<\/p>\n

\"\"<\/a>
Global temperatures since the beginning of complex life on Earth. The PETM is the highest spike in the green line \u2013 it hasn\u2019t been nearly as hot since.<\/span>
\nGlen Fergus \/ wiki<\/a>, CC BY-SA<\/a><\/span><\/figcaption><\/figure>\n

 <\/p>\n

Against the background of this \u201cgreenhouse world\u201d, the planet warmed by at least a further 5\u00b0C over a few thousand years<\/a> at the onset of the PETM. Life in the deep sea suffered disproportionately; many species went extinct and parts of the deep ocean became anoxic<\/a> (oxygen depleted). On land, the water cycle strengthened, leading to both floods and droughts. It took about 150,000 years for Earth\u2019s climate to naturally recover from this \u201cfever\u201d and regain some sort of equilibrium.<\/p>\n

Here\u2019s the really worrying part: 5\u00b0C over a few thousand years is breakneck speed in geological terms, but is still nothing compared to our current rate of warming. In fact, if we keep burning fossil fuels at our current rate, the worst-case scenarios<\/a> suggest we could hit 5\u00b0C by the end of the century.<\/p>\n

Blame the volcanoes<\/h2>\n

So what can the PETM tells us about the future? It has long been suspected that the warm period was triggered by increasing greenhouse gas concentrations in the atmosphere. These gases absorb and trap solar heat, which is why any significant increase unavoidably leads to global warming.<\/p>\n

We know there was a huge release of \u201cnew\u201d carbon into the atmosphere and oceans at the time, thanks to analysis of 56m-year-old sediments. Yet where this carbon came from has always been disputed. Carbon can be emitted as carbon dioxide or methane (aka CH\u2084) and both are greenhouse gases. Some say the PETM carbon was methane from marine sediments<\/a>, while others have advocated methane from thawing Antarctic permafrost<\/a> or the impact of a large comet<\/a> releasing carbon from rocks.<\/p>\n

\"\"<\/a>
The Mid-Atlantic Ridge is the longest mountain range in the world but is almost entirely underwater.<\/span>
\nUSGS \/ wiki<\/a><\/span><\/figcaption><\/figure>\n

 <\/p>\n

In our study recently published in Nature<\/a>, we identified the distinctive chemical fingerprint of this carbon \u2013 it pointed not to methane, but to emissions from intense and prolonged volcanic activity. We also show that atmospheric CO\u2082 levels more than doubled in less than 25,000 years.<\/p>\n

This makes sense: at the same time, Greenland and North America were drifting away from Europe, creating the North Atlantic Ocean and a string of volcanic activity<\/a> along what is now the Mid-Atlantic Ridge.<\/p>\n

We found more than 10,000 Gigatonnes of carbon must have been released into the atmosphere by volcanic activity during the PETM, which is an order of magnitude higher than all currently-accessible fossil fuel reserves<\/a> taken together.<\/p>\n

But the rate of emissions would have been at least 20 times slower than today<\/a>. Given how much CO\u2082 was released, the resulting global warming was about what we would predict based on calculations of current climate sensitivity.<\/p>\n

So what would volcanoes large enough to affect the climate like this actually look like, in practice? We could imagine a series of sky-blackening eruptions along the lines of Laki in Iceland<\/a> which caused temperatures to drop across the Northern Hemisphere<\/a> when it erupted in the 18th century. But, given we know the PETM volcanism largely took place under water and at a slower pace, perhaps the best modern equivalent would be the \u201cblack smokers\u201d still found today in the deep North Atlantic \u2013 but lots of them.<\/p>\n