A shutdown or thermohaline circulation slowing is the effect of global warming on large ocean circulation.
Data from NASA in 2010 suggested that Atlantic Meridional Overturning Circulation (AMOC) did not slow, but may have actually increased slightly since 1993. A 2015 study showed that AMOC had weakened by 15-20% in 200 years.
Video Shutdown of thermohaline circulation
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Don Chambers from the University of South Florida's College of Marine Sciences mentions, "The main impact of the slowing AMOC is expected to be the cooler winters and summers around the North Atlantic, and small regional elevations at sea level on the coast of North America." James Hansen and Makiko Sato stated,
The slowing of the AMOC which causes cooling of ~ 1 Â ° C and may affect weather patterns is very different from the AMOC shutdown that cools the North Atlantic a few degrees Celsius; the latter will have a dramatic effect on the storm and become irreversible on the timescale of the century.
The decline of Atlantic Atlantic dotted circulation, has been attributed to the extreme regional sea level rise.
The 2017 review concludes that there is strong evidence for past changes in AMOC strength and structure during sudden climatic events such as Younger Dryas and many Heinrich events.
Slowdown
Lohmann and Dima 2010 find the weakening of AMOC since the late 1930s. Climate scientists Michael Mann of Penn State and Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research suggested that the observed cold pattern for years of temperature records is a sign that Meridional Atlantic Oceanic (AMOC) circulation may be weakening. They published their findings in 2015, and concluded that AMOC circulation showed a remarkable decline in the last century, and that the melting of Greenland was a possible contributor, with an unprecedented 1970s AMOC slowdown over the last millennium.
A study published in 2016 found further evidence for the substantial impact of sea level rise for the US East Coast. The study confirms previous research findings that identify the area as a hotspot for sea level rise, with the potential to divert 3-4 times in the rate of increase, compared with the global average. The researchers attributed the possibility of an increase to the mechanism of ocean circulation called deep water formation, which is reduced due to the slowing AMOC, which causes the water bag warmer below the surface. In addition, the study notes, "Our results show that higher carbon emission levels also contribute to the increase in [[sea level rise] in this region compared to the global average."
Shutdown
Global warming can, through the cessation of thermohaline circulation, trigger cooling in the North Atlantic, Europe, and North America. This will mainly affect areas such as the British Isles, French and Nordic countries, which are warmed by the North Atlantic currents. Major consequences, apart from regional cooling, may also include increased flooding and storm, plankton stock collapse, warming or rainfall changes in the tropics or Alaska and Antarctica, more frequent and intense El Nià ± o events due to the corresponding cessation of Kuroshio, Leeuwin and East Australian Currents connected to the same thermohaline circulation as the Gulf Stream, or an oceanic oxygen-anoxic event ( O
2 ) beneath stagnant sea surface becomes completely depleted - possibly the cause of mass extinction events in the past.
Maps Shutdown of thermohaline circulation
Weather effects
Hansen et al. 2015 finds that that a large halt or decrease from AMOC, aside from possibly contributing to extreme late Eemian events, will lead to a more general increase of bad weather. Additional surface cooling of the ice melt increases the surface and decreases the tropospheric temperature gradient, and causes a model simulation of the increase in eddy-latitude energy across the troposphere midlatitude. This in turn leads to an increase in the baroclinitas produced by a stronger temperature gradient, which provides energy for more severe weather events.
Many of the most memorable and devastating storms in eastern and western North America, known as hurricanes, are winter cyclones, though sometimes at the end of autumn or early spring, which produce close and often stormy winds large quantities of snow fell. Continued warming of low-lying ocean in the coming decade will provide more water vapor to strengthen the storm. If this tropical warming combined with the Atlantic Ocean is colder than the AMOC slowdown and eddy midlatitude energy increase, we can anticipate more severe baroclinic storms.
Hansen et al. the results at least show that strong cooling in the North Atlantic from AMOC shutdown does not create higher wind speeds. The increase in seasonal average wind speeds from the northeast relative to pre-industrial conditions is as much as 10-20%. An increase in the percentage of such wind speed in a storm means an increase in storm power dissipation by a factor of ~ 1.4-2, since the discharge of wind power is proportional to the cube of wind velocity. However, simulated changes refer to average seasonal winds averaged over large boxes, not individual storms.
Observation
2010 and earlier
In April 2004, the hypothesis that Gulf Flow was off received a boost when a retrospective analysis of US satellite data seems to indicate a slowdown in the North Atlantic Gyre, the northern Gulf Stream vortex.
In May 2005, Peter Wadhams reported in The Times about the results of a submarine investigation beneath the Arctic ice sheet that measured the cool chimney of cold cold water, where cold and dense water usually drowned. to the seabed and replaced with warm water, forming one of the engines of the North Atlantic. He and his team found the chimney almost disappeared. Usually there are seven to twelve columns of giants, but Wadhams only find two giant columns, both very weak.
In 2005 a 30% reduction in warm currents carrying water to the north of the Gulf Stream was observed, from the last measurement in 1992. The authors noted the uncertainty in the measurements. After a media discussion, Detlef Quadfasel showed that Bryden's uncertainty estimates et al. high, but said other factors and observations support their results, and the implications based on paleoclimate notes show air drops. temperatures up to 10 ° C in decades, associated with a sudden ocean circulature switch when a certain threshold is reached. He concludes that further observation and modeling is essential to provide early warning of possible circulatory damage. In response, Quirin Schiermeier concludes that natural variation is the culprit for observation but highlights the possible implications.
In 2008, Vage et al. reported "the return of convection in to the subpolar pie both in the Labrador and Irminger seas in the winter of 2007-2008," using "floating data profiles from the Argo program to document mixing in," and "various in situ, satellites and reanalysis data" to set the context for the phenomenon. This may have a lot to do with observing the variations in cold water chimney behavior.
In January 2010, the Gulf Stream briefly connected with the West Greenland Current after fluctuating for several weeks due to the extreme negative phase of the Arctic oscillation, while diverting it to west Greenland.
Thermohaline and fresh water circulation
Heat is transported from the equatorial pole largely by the atmosphere but also by ocean currents, with warm water near the surface and cold water at a deeper level. The best known segment of this circulation is the Gulf Stream, a wind-driven gyre, which carries warm water from the Caribbean to the north. The northern branch of the Gulf Stream, North Atlantic Drift, is part of the thermohaline (THC) circulation, transporting warmth further north into the North Atlantic, where its effect in atmospheric warming contributes to European warming. Other factors are also important, such as atmospheric waves that bring more subtropical air to the north, which has been suggested to influence the British Isles climate more than the Gulf Stream.
Evaporation of sea water in the North Atlantic increases the salinity of water and cools it, both measures increase the water density on the surface. The formation of sea ice further increases salinity and density, because salt is ejected to the sea when sea ice is formed. The solid water then sinks and the circulation flow continues to the south. However, Atlantic Meridus Overtination Circulation (AMOC) is driven by sea temperatures and salinity differences. But freshwater lowers the salinity of seawater, and through this process prevents the cooler water from drowning. This mechanism may lead to anomalous cold-surface temperatures currently observed near Greenland (Cold blob (North Atlantic)).
Global warming could lead to an increase in freshwater in the northern oceans, by melting glaciers in Greenland, and by increasing rainfall, especially through the Siberian river.
An AMOC shutdown may be able to trigger a kind of sudden large temperature shift that occurs during the last glacial period: a series of Dansgaard-Oeschger events - rapid climate fluctuations - probably caused by freshwater pressure at high latitudes that interfere with THC. The 2002 model runs where the THC is forced to turn off performing local - cooling shows up to 8 Â ° C (14 Â ° F).
Studies from the Florida Current show that the Gulf Stream is weakening with cooling, becoming weakest (by ~ 10%) during Little Ice Age.
gyre Subpolar
Recent studies (2017) demonstrate the potential for the destruction of convection (heat transport) from sub-polar pie in the North Atlantic, resulting in rapid cooling, with implications for economic sectors, agricultural industries, water resources and energy management in Western Europe and the East Coast of the United States. Frajka-Williams et al. 2017 shows that recent changes in subpolar gyre cooling, warm temperatures in subtropics and cold anomalies in the tropics, increase the spatial distribution of meridian gradients in sea-surface temperatures, which are not captured by the AMO Index.
IPCC model
Based on the Atmosphere-Ocean General Circulation Model from 2001, THC tends to weaken somewhat rather than stop, and the heating effect is greater than cooling, even in Europe. In the IPCC Fifth Assessment Report, it is reported that is highly unlikely that AMOC will experience a rapid transition ( high confidence ).
In popular culture
The Day After Tomorrow film exaggerates the scenarios associated with AMOC closure.
See also
- 8.2 kiloyear event
- Mexican Gulf Circle Flow
- Anoxic events of the oceans
- Climate security
- Pacific Decadal Oscillation
- Paleocalinity, a change that is considered to slow THC
- Greenland Current West
References
External links
- THOR University of Hamburg project to study thermohaline circulation
- "Immediate Climate Change Scenario and Its Implications for United States National Security" (study 2003)
- What If Conveyor Will Be Closed? Reflections on Possible Results from Large Global Experiments (Research 1999)
- Nasty's Nasty at the Greenhouse (Video about the cessation of thermohaline circulation, 2015)
- Why is there a thermohaline circulation in the Atlantic but not in the Pacific? (2005 technical report)
Source of the article : Wikipedia
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