Crippled Atlantic currents triggered ice age climate change

Science, By Eric Hand, June 30

The last ice age wasn’t one long big chill. Dozens of times temperatures abruptly rose or fell, causing all manner of ecological change. Mysteriously, ice cores from Greenland and Antarctica show that these sudden shifts—which occurred every 1500 years or so—were out of sync in the two hemispheres: When it got cold in the north, it grew warm in the south, and vice versa. Now, scientists have implicated the culprit behind those seesaws—changes to a conveyor belt of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC).

These currents, which today drive the Gulf Stream, bring warm surface waters north and send cold, deeper waters south. But they weakened suddenly and drastically, nearly to the point of stopping, just before several periods of abrupt climate change, researchers report today in Science. In a matter of decades, temperatures plummeted in the north, as the currents brought less warmth in that direction. Meanwhile, the backlog of warm, southern waters allowed the Southern Hemisphere to heat up.

AMOC slowdowns have long been suspected as the cause of the climate swings during the last ice age, which lasted from 110,000 to 15,000 years ago, but never definitively shown. The new study “is the best demonstration that this indeed happened,” says Jerry McManus, a paleo-oceanographer at Columbia University’s Lamont-Doherty Earth Observatory, and a study author. “It is very convincing evidence,” adds Andreas Schmittner, a climate scientist at Oregon State University, Corvallis. “We did not know that the circulation changed during these shorter intervals.”

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  • Scientists: Window for avoiding 1.5C global warming ‘closed’

    Climate Home, By Megan Darby, June 29

    The 1.5C global warming limit vulnerable countries fought hard to include in the Paris Agreement may already be out of reach.

    There is slim chance of stabilising temperature rise at that level without controversial negative emissions technology, according to a study published in Nature.

    “The window for limiting warming to below 1.5C with high probability and without temporarily exceeding that level already seems to have closed,” the report found.

    […]

    In the most up-to-date analysis available, researchers found national climate pledges were consistent with temperature rise of 2.6-3.1C above pre-industrial levels.

    Nature: Paris Agreement climate proposals need a boost to keep warming well below 2 °C


    AFP: 31 scientific societies just told Congress to take their climate denial and shove it

    Scientists have had enough of Congress’ climate denial. On Tuesday, a whopping 31 major scientific groups — representing tens of thousands of researchers — delivered a joint letter to Capitol Hill to present a unified front on the seriousness of human-caused global warming and the need to address it.

    The 3-page letter, which is a more forceful version of a 2009 letter to which 19 scientific societies signed on, comes as the House Science Committee continues to investigate peer reviewed studies of climate change.

    It also landed on Congress’ doorstep as House lawmakers are maneuvering to block the Pentagon from spending money to implement its plan to adapt to global warming and prepare for the more unstable world it is ushering in.

    In addition, money to fund climate adaptation efforts in developing countries, which is a key part of the Paris Climate Agreement, is also on the chopping block in negotiations between the House and Senate.


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