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Scientist Predicts a Sixth Mass Extinction in 2100

1 earth, Environment, extinction 4:34 PM

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<tr><td class="tr-caption" style="text-align: center;">Some species made extinct by humans.</td></tr>
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<i><span style="font-family: "georgia" , "times new roman" , serif;">In the past 540 million years, the Earth has endured five mass extinction events, each involving processes that upended the normal cycling of carbon through the atmosphere and oceans. These globally fatal perturbations in carbon each unfolded over thousands to millions of years, and are coincident with the widespread extermination of marine species around the world.</span></i><br />
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The question for many scientists is whether the carbon cycle is now experiencing a significant jolt that could tip the planet toward a sixth mass extinction. In the modern era, carbon dioxide emissions have risen steadily since the 19th century, but deciphering whether this recent spike in carbon could lead to mass extinction has been challenging. That's mainly because it's difficult to relate ancient carbon anomalies, occurring over thousands to millions of years, to today's disruptions, which have taken place over just a little more than a century.<br />
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Now Daniel Rothman, professor of geophysics in the MIT Department of Earth, Atmospheric and Planetary Sciences and co-director of MIT's Lorenz Center, has analyzed significant changes in the carbon cycle over the last 540 million years, including the five mass extinction events. He has identified "thresholds of catastrophe" in the carbon cycle that, if exceeded, would lead to an unstable environment, and ultimately, mass extinction.<br />
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In a paper published in Science Advances, he proposes that mass extinction occurs if one of two thresholds are crossed: For changes in the carbon cycle that occur over long timescales, extinctions will follow if those changes occur at rates faster than global ecosystems can adapt. For carbon perturbations that take place over shorter timescales, the pace of carbon-cycle changes will not matter; instead, the size or magnitude of the change will determine the likelihood of an extinction event.<br />
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Taking this reasoning forward in time, Rothman predicts that, given the recent rise in carbon dioxide emissions over a relatively short timescale, a sixth extinction will depend on whether a critical amount of carbon is added to the oceans. That amount, he calculates, is about 310 gigatons, which he estimates to be roughly equivalent to the amount of carbon that human activities will have added to the world's oceans by the year 2100.<br />
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Does this mean that mass extinction will soon follow at the turn of the century? Rothman says it would take some time -- about 10,000 years -- for such ecological disasters to play out. However, he says that by 2100 the world may have tipped into "unknown territory."<br />
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"This is not saying that disaster occurs the next day," Rothman says. "It's saying that, if left unchecked, the carbon cycle would move into a realm which would be no longer stable, and would behave in a way that would be difficult to predict. In the geologic past, this type of behavior is associated with mass extinction."<br />
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<b><span style="font-family: "georgia" , "times new roman" , serif;">History follows theory</span></b><br />
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Rothman had previously done work on the end-Permian extinction, the most severe extinction in Earth's history, in which a massive pulse of carbon through the Earth's system was involved in wiping out more than 95 percent of marine species worldwide. Since then, conversations with colleagues spurred him to consider the likelihood of a sixth extinction, raising an essential question:<br />
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"How can you really compare these great events in the geologic past, which occur over such vast timescales, to what's going on today, which is centuries at the longest?" Rothman says. "So I sat down one summer day and tried to think about how one might go about this systematically."<br />
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He eventually derived a simple mathematical formula based on basic physical principles that relates the critical rate and magnitude of change in the carbon cycle to the timescale that separates fast from slow change. He hypothesized that this formula should predict whether mass extinction, or some other sort of global catastrophe, should occur.<br />
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Rothman then asked whether history followed his hypothesis. By searching through hundreds of published geochemistry papers, he identified 31 events in the last 542 million years in which a significant change occurred in Earth's carbon cycle. For each event, including the five mass extinctions, Rothman noted the change in carbon, expressed in the geochemical record as a change in the relative abundance of two isotopes, carbon-12 and carbon-13. He also noted the duration of time over which the changes occurred.<br />
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He then devised a mathematical transformation to convert these quantities into the total mass of carbon that was added to the oceans during each event. Finally, he plotted both the mass and timescale of each event.<br />
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"It became evident that there was a characteristic rate of change that the system basically didn't like to go past," Rothman says.<br />
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In other words, he observed a common threshold that most of the 31 events appeared to stay under. While these events involved significant changes in carbon, they were relatively benign -- not enough to destabilize the system toward catastrophe. In contrast, four of the five mass extinction events lay over the threshold, with the most severe end-Permian extinction being the farthest over the line.<br />
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"Then it became a question of figuring out what it meant," Rothman says.<br />
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<b><span style="font-family: "georgia" , "times new roman" , serif;">A hidden leak</span></b><br />
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Upon further analysis, Rothman found that the critical rate for catastrophe is related to a hidden process within the Earth's natural carbon cycle. The cycle is essentially a loop between photosynthesis and respiration. Normally, there is a "leak" in the cycle, in which a small amount of organic carbon sinks to the ocean bottom and, over time, is buried as sediment and sequestered from the rest of the carbon cycle.<br />
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Rothman found that the critical rate was equivalent to the rate of excess production of carbon dioxide that would result from plugging the leak. Any additional carbon dioxide injected into the cycle could not be described by the loop itself. One or more other processes would instead have taken the carbon cycle into unstable territory.<br />
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He then determined that the critical rate applies only beyond the timescale at which the marine carbon cycle can re-establish its equilibrium after it is disturbed. Today, this timescale is about 10,000 years. For much shorter events, the critical threshold is no longer tied to the rate at which carbon is added to the oceans but instead to the carbon's total mass. Both scenarios would leave an excess of carbon circulating through the oceans and atmosphere, likely resulting in global warming and ocean acidification.<br />
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<b><span style="font-family: "georgia" , "times new roman" , serif;">The century's the limit</span></b><br />
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From the critical rate and the equilibrium timescale, Rothman calculated the critical mass of carbon for the modern day to be about 310 gigatons.<br />
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He then compared his prediction to the total amount of carbon added to the Earth's oceans by the year 2100, as projected in the most recent report of the Intergovernmental Panel on Climate Change. The IPCC projections consider four possible pathways for carbon dioxide emissions, ranging from one associated with stringent policies to limit carbon dioxide emissions, to another related to the high range of scenarios with no limitations.<br />
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The best-case scenario projects that humans will add 300 gigatons of carbon to the oceans by 2100, while more than 500 gigatons will be added under the worst-case scenario, far exceeding the critical threshold. In all scenarios, Rothman shows that by 2100, the carbon cycle will either be close to or well beyond the threshold for catastrophe.<br />
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"There should be ways of pulling back [emissions of carbon dioxide]," Rothman says. "But this work points out reasons why we need to be careful, and it gives more reasons for studying the past to inform the present."<br />
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<u><i><span style="font-family: "trebuchet ms" , sans-serif;">The above story is based on <a href="http://news.mit.edu/2017/mathematics-predicts-sixth-mass-extinction-0920" rel="nofollow" target="_blank">Materials</a> provided by <a href="http://web.mit.edu/" rel="nofollow" target="_blank">Massachusetts Institute of Technology</a>. Original written by Jennifer Chu.</span></i></u></div>

Scientist Predicts a Sixth Mass Extinction in 2100

Some species made extinct by humans. In the past 540 million years, the Earth has endured five mass extinction events, each involving...

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What Caused Mexico's Latest Earthquakes

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What Caused Mexico's Latest Earthquakes

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At Least 105 Killed as Powerful 7.1 Earthquake Strikes Central Mexico

0 Earthquakes, News 2:46 AM

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<tr><td class="tr-caption" style="text-align: center;">People cleared the rubble of a damaged building in Mexico City after a major earthquake struck on Tuesday, the second to hit the country in less than two weeks. Credit Alfredo Estrella/Agence France-Presse — Getty Images</td></tr>
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<i><span style="font-family: "georgia" , "times new roman" , serif;">A powerful 7.1-magnitude earthquake struck central Mexico on Tuesday, collapsing buildings and killing dozens of people on the anniversary of a 1985 quake that devastated Mexico City.</span></i><br />
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Coming less than two weeks after a deadly temblor off Mexico’s Pacific coast, and just hours after a siren signaled an annual earthquake drill in the capital, Tuesday’s quake shook the ground with terrifying force, buckling walls and sending panicked residents fleeing into the streets. There were reports of fires and gas leaks.<br />
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At least 107 people were reported killed, local officials and news agencies reported. They included 42 people in Morelos state south of Mexico City, 26 in the state of Puebla, nine in the state of Mexico — which surrounds the capital — and 30 in Mexico City.<br />
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</div>Residents feared more people were buried under rubble. At least 29 buildings crumbled in the massive capital, officials said. In the central Mexico City neighborhood of Del Valle, a frantic scene played out Tuesday afternoon as hundreds of people gathered to search for trapped residents. At least two multistory apartment buildings tumbled down and residents said dozens of people could have been inside at the time. Marines, medical volunteers and regular citizens formed lines to pass in trash cans, plastic crates, and plastic barrels, to fill with debris.<br />
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Rescue workers carried at least one person out on a stretcher while helicopters circled overhead.<br />
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The U.S. Geological Survey said the epicenter of the quake was 76 miles southeast of the capital, near the town of Raboso in Puebla. It struck at 1:14 p.m. local time, the agency said. There appeared to be widespread damage, including to a major highway connecting Mexico City to Cuernavaca, the capital of Morelos located about 35 miles to the south. Authorities shut the Mexico City airport to look for damage.<br />
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At the Clínica Gabriel Mancera in Mexico City, more than a dozen hospital beds had been set up in the patio outside as a triage center on Tuesday afternoon. Leticia Gonzalez, a 45-year-old maid in a nearby apartment building, said she tried to race out of the building but that concrete crashed down as she fled. Her right leg was wrapped in a bandage as she grimaced in pain outside the hospital.<br />
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“We were all running like crazy,” she said. “This was the worst earthquake I’ve ever seen.”<br />
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Marisela Avila Gomez, 58, was in her apartment in the central Narvarte neighborhood in the capital when the shaking began, toppling her furniture and shattering the windows. A piece of glass sliced deep into her right leg.<br />
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</div>“I lost about three liters of blood,” she said. “My whole house is full of blood.”<br />
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Her husband, Francisco Vicente Lozada Garcia, a 55-year-old landscaper, tried to drive across town to get to his wife, but traffic was snarled and the “street felt like gelatin.”<br />
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The couple eventually made it to the Clinica Gabriel Mancera, where Avila Gomez was treated.<br />
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The earthquake struck less than two weeks after the 8.1-magnitude quake off the Pacific coast of southern Mexico. Scientists said the same large-scale tectonic mechanism led to both events: the larger North American Plate is forcing the edge of the Cocos Plate to sink. This collision generated both quakes. But it was unlikely the quake earlier this month caused Tuesday’s disaster.<br />
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“In general, we don’t think there’s a triggering effect over that kind of a distance,” said Don Blakeman, a geophysicist with the U.S. Geological Survey. In California, he said, there have been earthquakes that set off quakes tens of miles away and within hours of each other. This distance was farther and the timeline longer. The recent Mexico quakes did not share a fault line, he said.<br />
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Mexico City is partially built on old lake sediment, which is much softer than rock. The seismic waves can be amplified traveling through the sediment, Blakeman said, making the damage worse than in areas on more solid ground. He said aftershocks were possible, too. The rupture was approximately 50 kilometers, or 31 miles deep, and as a rule the shallower an earthquake is the higher the chance for aftershocks. “Fifty kilometers is pretty shallow so I would expect aftershocks,” Blakeman said.<br />
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The U.S. Geological Survey’s model for estimating earthquake damage predicts 100 to 1,000 fatalities and economic losses of between $100 million and $1 billion for a temblor of this scale and proximity to population centers.<br />
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The quake shook Mexico City so hard it tossed the murky, stagnant waters of the city’s ancient Xochmilco canals, turning the waterways into rollicking wave pools. Videos posted to social media showed tourists in flat-bottomed trajinera boats struggling to stay in their seats and hold onto their beers.<br />
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