The North Atlantic ocean current, which warms northern Europe, may be slowing

The North Atlantic ocean current, which warms northern Europe, may be slowing

SOURCE: Yale Climate Connections DATE: August 15, 2019 SNIP: A stubborn blue spot of cool ocean temperatures stands out like the proverbial sore thumb in a recent NASA image of the warming world – a circle of cool blue on a planet increasingly shaded in hot red. A region of the North Atlantic south of Greenland has experienced some of its coldest temperatures on record in recent years, a cooling unprecedented in the past thousand years. What explains that anomaly? Climatologist Michael Mann of Penn State University, in this month’s “This is Not Cool” video, explains that this phenomenon may be an indication that the North Atlantic current, part of a larger global ocean circulation, is slowing down. Stefan Rahmstorf of the University of Potsdam, Germany, says this circulation – called the thermohaline circulation, but popularly known to many in the U.S. as “the Gulf Stream” – keeps northern Europe several degrees warmer than it would otherwise be at that latitude. [T]he consequences of a shutdown would be serious for agriculture – and for temperate weather – in northern Europe. “We are 50 to a hundred years ahead of schedule with the slowdown of this ocean circulation pattern, relative to the models,” according to Mann. “The more observations we get, the more sophisticated our models become, the more we’re learning that things can happen faster, and with a greater magnitude, than we predicted just years...
Climate Model Predicts Faster Warming for the North Atlantic Ocean

Climate Model Predicts Faster Warming for the North Atlantic Ocean

SOURCE: Scripps Institution of Oceanography DATE: August 14, 2018 SNIP: Researchers at Scripps Institution of Oceanography at UC San Diego have predicted faster rates of warming than previously predicted for the North Atlantic Ocean in a recent paper published in the Journal of Climate. This warming could disrupt major oceanic cycles and have worldwide impacts on climate systems. The researchers modeled scenarios based on possible future greenhouse gas and aerosol emission rates. One likely scenario focuses on future decline in aerosols and continued increase of greenhouse gases in the atmosphere. Aerosols are minute particles suspended in the atmosphere. Some scatter sunlight, thereby actually acting as cooling agents. The aerosol cooling effect is about 50 percent of the warming effect of anthropogenic carbon dioxide at present. Aerosols released from human activities are pollutants, however, and their health concerns have triggered worldwide efforts to curb emissions. An aerosol decline could spark an interesting catch-22: Because of their cooling effect, this decline would accelerate ocean warming that is already being caused by increasing carbon dioxide emissions–most notably initiating major warming in the North Atlantic. With a decrease in cooling aerosols, which are concentrated in the Northern Hemisphere, over time the ocean would need to absorb more heat. The researchers predict that the North Atlantic’s share of the uptake could increase from 6 percent to about 27...
Sluggish Atlantic circulation could cause global temperatures to surge

Sluggish Atlantic circulation could cause global temperatures to surge

SOURCE: Nature DATE: July 18, 2018 SNIP: In a paper in Nature, Chen and Tung report that the system of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC) can explain changes in rates of global surface warming. Rather than the conventional picture of a vigorous AMOC associated with elevated surface temperatures in the Atlantic Ocean, the authors emphasize the role of the AMOC in taking heat from the surface and storing it in the deep ocean. Atmospheric concentrations of greenhouse gases are currently being increased at a rate that is unprecedented in millennia and most likely millions of years. As a result, the role that climate mechanisms might have had in the past might not be a good guide to their current or future role. The authors contend that half of the heat arising from ever-increasing greenhouse-gas concentrations is stored in the deep waters of the North Atlantic when the AMOC is increasing, thereby reducing overall global surface warming. The authors show that a cycle of increasing and then decreasing AMOC from the 1940s to the mid-1970s coincided with a period of global-warming slowdown; a quiescent period of weak AMOC from the mid-1970s to the late 1990s coincided with rapid global warming; and an increase in AMOC strength from the late 1990s to 2005 and a decrease thereafter coincided with the ‘hiatus’ in global warming. The AMOC is deemed “very likely” to weaken in the coming decades. Indeed, the Atlantic has seen muted rises in surface temperature relative to the global ocean over the past few decades. This relative lack of warming has been interpreted as a...
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...