Gulf Stream current at its weakest in 1,600 years, studies show

Gulf Stream current at its weakest in 1,600 years, studies show

SOURCE: The Guardian and Real Climate DATE: April 11, 2018 SNIP: The warm Atlantic current linked to severe and abrupt changes in the climate in the past is now at its weakest in at least 1,600 years, new research shows. The findings, based on multiple lines of scientific evidence, throw into question previous predictions that a catastrophic collapse of the Gulf Stream would take centuries to occur. Such a collapse would see western Europe suffer far more extreme winters, sea levels rise fast on the eastern seaboard of the US and would disrupt vital tropical rains. The new research shows the current is now 15% weaker than around 400AD, an exceptionally large deviation, and that human-caused global warming is responsible for at least a significant part of the weakening. Scientists know that the Atlantic Meridional Overturning Circulation (AMOC) has slowed since 2004, when instruments were deployed at sea to measure it. But now two new studies have provided comprehensive ocean-based evidence that the weakening is unprecedented in at least 1,600 years, which is as far back as the new research stretches. “AMOC is a really important part of the Earth’s climate system and it has played an important part in abrupt climate change in the past,” said Dr David Thornalley, from University College London who led one of the new studies. He said current climate models do not replicate the observed slowdown, suggesting that AMOC is less stable that...
The fast-melting Arctic is already messing with the ocean’s circulation, scientists say

The fast-melting Arctic is already messing with the ocean’s circulation, scientists say

SOURCE: Washington Post DATE: March 14, 2018 SNIP: Scientists studying a remote and icy stretch of the North Atlantic have found new evidence that fresh water, likely melted from Greenland or Arctic sea ice, may already be altering a key process that helps drives the global circulation of the oceans. In chilly waters on either side of Greenland, the ocean circulation “overturns,” as surface waters traveling northward become colder and more dense and eventually sink, traveling back southward toward Antarctica at extreme depths. This key sinking process is called convection. But too much fresh water at the surface could interfere with it, because with less salt, the water loses density and does not sink as easily. In the new research, Marilena Oltmanns and two colleagues at the GEOMAR Helmholtz Center for Ocean Research in Kiel, Germany, found that following particularly warm summers in the remote Irminger Sea, convection tended to be more impaired in winter. In some cases, a layer of meltwater stayed atop the ocean into the next year, rather than vanishing into its depths as part of the overturning circulation, which has sometimes been likened to an ocean “conveyor belt.” “Until now, models have predicted something for the future … but it was something that seemed very distant,” said Oltmanns, the lead scientist behind the research, which was published this week in Nature Climate Change. “But now we saw with these observations that there is actually freshwater and that it is already affecting convection, and it delays convection quite a lot in some years,” she...
Global Ocean Circulation Appears To Be Collapsing Due To A Warming Planet

Global Ocean Circulation Appears To Be Collapsing Due To A Warming Planet

SOURCE: Forbes DATE: Aug 3, 2017 SNIP: A recent study published in Nature outlines research by a team of Yale University and University of Southhampton scientists. The team found evidence that Arctic ice loss is potentially negatively impacting the planet’s largest ocean circulation system. While scientists do have some analogs as to how this may impact the world, we will be largely in uncharted territory. AMOC is one of the largest current systems in the Atlantic Ocean and the world. Evidence is growing that the comparatively cold zone within the Northern Atlantic could be due to a slowdown of this global ocean water circulation. Hence, a slowdown in the planet’s ability to transfer heat from the tropics to the northern latitudes. The cold zone could be due to melting of ice in the Arctic and Greenland. This would cause a cold fresh water cap over the North Atlantic, inhibiting sinking of salty tropical waters. This would in effect slow down the global circulation and hinder the transport of warm tropical waters...
Loss of Arctic sea ice impacting Atlantic Ocean water circulation system

Loss of Arctic sea ice impacting Atlantic Ocean water circulation system

SOURCE: Yale News DATE: July 31, 2017 SNIP: Arctic sea ice is not merely a passive responder to the climate changes occurring around the world, according to new research. Scientists at Yale University and the University of Southampton say the ongoing Arctic ice loss can play an active role in altering one of the planet’s largest water circulation systems: the Atlantic Meridional Overturning Circulation (AMOC). AMOC has a lower limb of dense, cold water that flows south from the north Atlantic, and an upper limb of warm, salty water that flows north from the south Atlantic as part of the Gulf Stream. AMOC plays a major role in regional and global climate, affecting the Atlantic rim countries — particularly those in Europe — and far beyond. Earlier this year, a different Yale-led study cautioned that the AMOC system was not as stable as previously thought. That study said the possibility of a collapsed AMOC under global warming conditions is being significantly underestimated. “We’ve now found this new connection between sea ice and AMOC,” Liu [Wei Liu, a Yale postdoctoral associate] said. “Sea ice loss is clearly important among the mechanisms that could potentially contribute to AMOC collapse.” “In our experiments we saw a potential loss of 30% to 50% of AMOC’s strength due to Arctic sea ice loss. That is a significant amount, and it would accelerate the collapse of AMOC if it were to occur,” Fedorov [Alexey Fedorov, climate scientist at the Yale Department of Geology and Geophysics]...
Drastic cooling in North Atlantic beyond worst fears, scientists warn

Drastic cooling in North Atlantic beyond worst fears, scientists warn

SOURCE: The Guardian DATE: February 24, 2017 SNIP: For thousands of years, parts of northwest Europe have enjoyed a climate about 5C warmer than many other regions on the same latitude. But new scientific analysis suggests that that could change much sooner and much faster than thought possible. Climatologists who have looked again at the possibility of major climate change in and around the Atlantic Ocean, a persistent puzzle to researchers, now say there is an almost 50% chance that a key area of the North Atlantic could cool suddenly and rapidly, within the space of a decade, before the end of this...