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...
Potential for Collapse of Key Atlantic Current Rises

Potential for Collapse of Key Atlantic Current Rises

SOURCE: Climate Central DATE: January 5, 2017 SNIP: The large, looping Atlantic Ocean current that keeps northwestern Europe fairly warm and influences sea levels along the U.S. coast is a key component of the Earth’s climate system. But because of global warming, it may be more likely to substantially slow down — or even collapse — than previously thought, according to two new studies. If that current, called the Atlantic Meridional Overturning Circulation, were to slow down substantially, it could lead to chillier weather in northern and western Europe, starve economically important fisheries and cause waters to rise along the U.S. coast, leading to more so-called “sunny day” flooding and storm surge when hurricanes come ashore. It could also shift tropical rain belts, causing major disruptions to regional climate in Central and South...