The Atlantic Meridional Overturning Circulation may be heading for collapse due to climate change, a study finds. The ocean system plays a critical role in redistributing heat and regulating weather patterns around the world. www.washingtonpost.com/climate-environment/2021/08/05/change-ocean-collapse-atlantic-meridional/
“We’re poking a beast. But we don’t really know the reaction we’ll cause.” — climate scientist on Atlantic Ocean current system breakdown www.nytimes.com/2021/08/05/us/gulf-stream-collapse.html?referringSource=articleShare
Where is the Gulf Stream?
The Gulf Stream is a strong ocean current that brings warm water from the Gulf of Mexico into the Atlantic Ocean. It extends all the way up the eastern coast of the United States and Canada. The Gulf Stream is a strong ocean current that brings warm water from the Gulf of Mexico into the Atlantic Ocean. scijinks.govWhat Is the Gulf Stream? | NOAA SciJinks – All About Weather
You've heard of the invisible hand of the market, the supposedly unseen force that drives an economy. Well, meet the unseen hand of the weather: the Gulf Stream. The powerful current that runs through the Atlantic Ocean helps to regulate temperatures across the Northern Hemisphere and serves as a vital sign of the planet's global health.
New research that checks in on the pulse of the Gulf Stream suggests that it might be on life support. According to a study published this week in the journal Nature and Climate Change, the current known as the Atlantic meridional overturning circulation (AMOC) has experienced "an almost complete loss of stability" over the last 100 years and is showing signs of approaching a complete collapse.
We've known that the Gulf Stream was in rough shape for a while now. Research published earlier this year warned that the current's pull was weaker than it has been in over 1,000 years. But the latest finding of researchers indicates that things are worse than we previously imagined. The findings indicate that the AMOC could collapse, falling from its status as a strong circulation that helps to control the climate on both sides of the Atlantic, to a weak circulation that is no longer capable of regulating temperatures.
Understanding how important the Gulf Stream is to the global climate requires knowing what exactly this invisible force does. Think of it as the Atlantic Ocean's conveyor belt. It grabs the warm surface waters from the Gulf of Mexico and carries them all the way up to Western Europe while sending the colder, deeper waters from that region back down south. The current is capable of moving as much as 20 million cubic meters of water per second, about 100 times the rate of movement of the Amazon River. In shifting those waters, the Gulf Stream influences the weather on the east coast of the U.S., Canada, western Europe, and Africa's western coast. The current helps to keep waters warmer during the winter month and has a cooling effect during the summer months that helps to regulate temperatures and stave off extreme weather events that might otherwise take advantage of more favorable and less controlled conditions.
If the Gulf Stream slows, it could spell disaster. The lack of that consistent and predictable current shifting around water could lead to dramatic sea level rises across the east coast of the U.S., extremely cold winters in Europe, and devastating disruptions during monsoon season in the tropics. Drier seasons could do major damage to essential crops in places like India, South America, and Africa, which depend on those annual upticks in precipitation to grow food that feeds billions of people.
None of that is good, and we aren't sure when exactly that collapse could happen, which creates an unsettling amount of uncertainty. Researchers warn that the switch from strong circulation to weak status could happen within the next decade or could take several centuries. But if we don't do something to address climate change, it'll likely happen sooner rather than later. The slowing of the current has occurred largely due to the increased amount of rainfall and the melting of ice sheets around Greenland, which has pushed lighter, warmer freshwater into the stream where dense, cold salt water is supposed to be. Those ice sheets are thawing because the planet is warming.
Reducing our greenhouse emissions and staving off more global temperature rises is the only way to keep the Earth's essential conveyor belt running. If it stops, it'll be like someone suddenly hitting the emergency stop on the treadmill while you're running. Things are going to change, fast, and it won't be pretty.
Read full article at The Jerusalem Post
07 August, 2021 - 11:50pm
The Gulf Stream is at its weakest in a millennia, approaching a 'tipping point' where it could collapse and push temperatures in Europe down by 18F, a new study has warned.
Human caused climate change is responsible for changes bringing the current - also known as the Atlantic Meridional Overturning Circulation (AMOC) - to the brink of collapse, according to the Potsdam Institute for Climate Impact Research, Germany.
The Atlantic Ocean circulation system is responsible for the mild temperatures in the UK and Europe, moving heat from the tropics to the northern hemisphere.
Its underlying system has become destabilised, researchers discovered, which could eventually result in it switching to a 'weak mode' and lead to its collapse.
It is currently only approaching 'tipping point', but when it happens warm water won't be moved up through western Europe, causing freezing cold winters.
Study authors can't say when it will happen as there is still the chance to stop it, but it would require a dramatic reduction in carbon emissions.
'At the moment we most likely haven't already crossed the critical threshold,' study author Niklas Boers told MailOnline, adding 'every single gram of CO2 we don't emit into the atmosphere will reduce the probability that we'll cross the threshold'.
Ocean currents play a critical role in regulating the planet.
They are the continuous, predictable, directional movement of sea water by gravity, wind, and water density.
Water in the ocean moves in two directions - horizontally and vertically.
Horizontal movements are referred to as currents, while vertical changes are called upwellings or downwellings.
Slower circulation in the North Atlantic can yield profound change.
This is on both the North American and European climate but also on African and Asian summer monsoon rainfall.
This is through its effect on sea surface temperature, hydrological cycle, atmospheric circulation and variation in the intertropical convergence zone.
If the Gulf Stream, moving warm water up from the tropics, collapses Europe would be plunged into a deep freeze.
Disaster movie The Day After Tomorrow was based on the collapse of AMOC, the phenomenon that drives the gulf stream, carrying warm surface water from the equator and return it cold back tot he bottom of the Atlantic.
The AMOC is known to be at its weakest in more than 1,000 years based on an earlier study, and this new research explored whether it was due to an underlying stability.
A collapse was previously considered unlikely under current global warming levels, with the system slowly weakening over the last century.
Lead author Dr Niklas Boers, of the Potsdam Institute for Climate Impact Research, Germany, explored the underlying dynamical stability of the AMOC.
'The loss of dynamical stability would imply that the AMOC has approached its critical threshold beyond which an abrupt and potentially irreversible transition to the weak mode could occur,' he explained.
The analysis was based on 'fingerprints' the AMOC leaves in surface temperature and salinity patterns.
It showed a 'critical threshold' is being reached beyond which the system may collapse, although we haven't reached that point yet.
The finding was both alarming and surprising, as the scenario was expected to occur at global warming levels much higher than the current increases.
'Most evidence suggests the recent AMOC weakening is caused directly by the warming of the northern Atlantic ocean,' said Dr Boers.
'But according to our understanding, this would be unlikely to lead to an abrupt state transition.
'Stability loss that could result in such a transition would be expected following the inflow of substantial amounts of freshwater into the North Atlantic in response to melting of the Greenland ice sheet, melting Arctic sea ice and an overall enhanced precipitation and river runoff.'
Fresh water from melting ice - especially in Greenland - has accelerated in the last few decades, with regional destabilisation of the Greenland Ice sheet already detected.
Dr Boers added: 'To understand this in-depth we need to find ways to improve the representation of the AMOC and polar ice sheets in comprehensive Earth system models and to better constrain their projections.
'I hope that the results presented here will help with that.'
He said that while it is weakening, it hasn't reached the tipping point yet, and this study simply shows that the AMOC is still in its strong circulation mode.
David Thornalley, an expert in the AMOC from University College London, not involved in this study, said there is evidence the modern AMOC could suddenly switch to a new, weaker state.
'But we don’t know for certain if this can happen, and if it can, how close we might be to any such tipping point,' he said.
The Atlantic Meridional Overturning Circulation (AMOC) is a large system of ocean currents.
They carry warm water from tropics northwards into the North Atlantic.
Like a conveyor belt, driven by differences in temperature and salt content – the water's density.
As warm water flows northwards it cools and some evaporation occurs, which increases the amount of salt.
Low temperature and a high salt make the water denser, and this dense water sinks deep into the ocean.
The cold, dense water slowly spreads southwards, several kilometres below the surface.
Eventually, it gets pulled back to the surface and warms in a process called 'upwelling' and the circulation is complete.
This global process makes sure that the world's oceans are continually mixed, and that heat and energy are distributed around the earth.
This, in turn, contributes to the climate we experience today.
Adding: 'We still don’t know how close we might be to a future tipping point, and if indeed one exists.
'But this study provides evidence to suggest that there may be a loss in stability of the AMOC that is consistent with the idea of an approaching tipping point.'
'The weak circulation mode is much much weaker than the present day mode, even if that has slowed down,' Dr Boers told MailOnline.
The team discovered that the decline in strength over the last century is associated with a loss of stability, rather than just a linear change in its mean state.
'So we have been moving closer to the critical threshold, but we certainly haven't moved into the weak circulation mode already,' he said.
'The concern is that we have moved closer to the critical point where a collapse to the weak mode can occur,' adding it would have dramatic consequences in terms of cooling Europe by up to 18F and impact on tropical monsoon systems.
'I reveal significant signs of stability loss, but it's hard to estimate from that where exactly the critical threshold is,' he told MailOnline.
'This is because there are too many uncertainties in translating our CO2 emissions into global warming, translating that to the actual warming in the Arctic, then translating that to the freshwater inflow to the North Atlantic via Greenland Ice Sheet and Sea Ice melting.
'Then there are still uncertainties in the exact value of freshwater inflow at which the AMOC will tip over to the weak mode.
'What can be said for sure is that we haven't expected to see such clear signs of stability loss at this point already. Once we reach the critical point, the AMOC will likely collapse within a few decades.'
It isn't beyond hope though, as Dr Boers told MailOnline 'every single gram of CO2 that we don't emit to the atmosphere will reduce the probability that we'll eventually cross the threshold and thus trigger the AMOC collapse.'
'This is certain even if the numbers themselves are uncertain,' he added.
Professor Mark Maslin, from University College London, not involved in this study, said it raises serious questions about the stability of North Atlantic ocean circulation.
'Increased instability could make European weather more variable, leading to more extreme events. But we do not know if the ocean circulation will collapse or how close we are to that critical threshold.'
David Alexander, Professor of Risk and Disaster Reduction at University College London, not involved in the research, said Britain is unprepared for a major disaster.
'Britain does not have a proper civil protection system,' he told MailOnline, with no national emergency operations centre, inadequate training an an 'excessive reliance on military assistance,' he said.
He added that 'almost all the vital areas have been starved of resources, there are no representatives of disaster science on SAGE and volunteer organisations are not properly incorporated into the system.'
'There is a failure to learn from other countries' good practices and a strong desire to emulate the United States, which is possibly the worst example to follow.'
'Despite the presence of an enormous well of talent and expertise in Britain, almost all disasters over the last 35 years have been badly managed.'
Professor Thornalley from UCL said: the study couldn't prove AMOC might undergo a sudden collapse in the future, but does add real-world evidence it may be more unstable than models currently suggest.
'The link between the AMOC and these fingerprints is still being debated and there are other processes that might also affect some of these ocean properties,' he said.
'Therefore the study might be showing increasing instability in a feature of ocean circulation (which is a concern in itself), but it might not be AMOC.
'However, it is reasonable to me to use this collection of different indicators to infer that it is likely they are detecting changes in AMOC.'
He said scientists should be cautious about the quality of the observational data from the early part of the record, as direct ocean measurements were sparse.
This 'could mean the variability in the first part of the record is not accurately captured, which could alter the assessment of long term trends in variability and stability,' said Thornalley.
The study is part of the EU's TiPES project which is investigating tipping points in the Earth system and is published in the journal Nature Climate Change.
If the AMOC was to collapse, far less heat would reach western Europe and the region would be plunged into very severe winters, the kind of scenario depicted in an extreme fashion in the movie The Day After Tomorrow.
Until the 1800s, it was relatively stable but the current declined after the so-called 'Little Ice Age' ended in 1850.
Temperatures dropped low enough that the River Thames completely froze over and records show Londoners crossing the waterway on foot.
The last shutdown was probably at the end of the last Ice Age, 12,000 years ago, and it prompted a temperature drop of 5°C to 10°C in western Europe.
In the event of another collapse, not only would European winters become much colder but summer droughts, storms and heatwaves would likely become more common.
Sea levels could rise up to nearly 20 inches around the North Atlantic Basin, which surrounds the eastern US coast.
This would eventually push people living along the coast further inland to escape flooding. A widespread collapse of deep-sea eco-systems would occur.
In the US, Florida would be particularly badly affected as the flow of water northwards would be halted, seeing it collect on the state's shoreline.
A study published last year looked at how the cessation of the AMOC may impact the UK specifically.
University of Exeter researchers made a computer model and found that by 2080 the weather would be 3.4°C colder than it was last year.
Rainfall during the growing season is expected to drop by 123mm, they added.
This, Ars Technica reports, is enough to reduce the UK's arable land from 32 percent to just seven percent, greatly affecting food production.
The effects would be felt not in Europe and the United States, with forecasts also projecting that the collapse of the AMOC would also increase drought in the Sahel in Africa.
07 August, 2021 - 11:50pm
The study, published in the journal Nature Climate Change, focuses on the Atlantic Meridional Overturning Circulation (AMOC), which includes the Gulf Stream. As the United Kingdom’s Met Office explains, it is “a large system of ocean currents that carry warm water from the tropics northwards into the North Atlantic,” like a conveyor belt.
Previous research has shown AMOC weakening in recent centuries. The author of the new study, Niklas Boers of the Potsdam Institute of Climate Impact Research (PIK), found that this is likely related to a loss of stability.
“The Atlantic Meridional Overturning is one of our planet’s key circulation systems,” Boers, who is also affiliated with universities in the U.K. and Germany, said in a statement.
“We already know from some computer simulations and from data from Earth’s past, so-called paleoclimate proxy records, that the AMOC can exhibit — in addition to the currently attained strong mode — an alternative, substantially weaker mode of operation,” he continued. “This bi-stability implies that abrupt transitions between the two circulation modes are in principle possible.”
In the absence of long-term data on the current system’s strength, Boers looked at its “fingerprints,” sea-surface temperature and salinity patterns. He said that “a detailed analysis of these fingerprints in eight independent indices now suggests that the AMOC weakening during the last century is indeed likely to be associated with a loss of stability.”
“The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures,” he continued, “but likely means the approaching of a critical threshold beyond which the circulation system could collapse.”
As The Guardian’s Damian Carrington reports, the collapse of “one of the planet’s main potential tipping points” would be devastating on a global scale:
Such an event would have catastrophic consequences around the world, severely disrupting the rains that billions of people depend on for food in India, South America, and West Africa; increasing storms and lowering temperatures in Europe; and pushing up the sea level in the eastern U.S. It would also further endanger the Amazon rainforest and Antarctic ice sheets.
The complexity of the AMOC system and uncertainty over levels of future global heating make it impossible to forecast the date of any collapse for now. It could be within a decade or two, or several centuries away. But the colossal impact it would have means it must never be allowed to happen, the scientists said.
“The signs of destabilization being visible already is something that I wouldn’t have expected and that I find scary,” Boers told the newspaper. “It’s something you just can’t [allow to] happen.”
It is unclear what level of global heating would cause a collapse, “so the only thing to do is keep emissions as low as possible,” he added. “The likelihood of this extremely high-impact event happening increases with every gram of CO2 that we put into the atmosphere.”
Some climate action advocates responded to the study by highlighting a science fiction movie that, as famed film critic Roger Ebert wrote nearly two decades ago, “is ridiculous, yes, but sublimely ridiculous — and the special effects are stupendous.”
This is literally the exact plot of the 2004 film The Day After Tomorrowhttps://t.co/MQRHRTq9oP
— Eric Holthaus (@EricHolthaus) August 5, 2021
“We all laughed at The Day After Tomorrow, back in 2004,” said Guy Shrubsole, policy and campaigns coordinator at Rewilding Britain. “Turned out it was a documentary.”
The environmental advocacy group 350 Tacoma responded to the findings with a call to action.
“There are warning signs that the Gulf Stream could collapse, an unimaginably catastrophic (and irreversible) impact of fossil fuel-caused climate breakdown,” the group tweeted. “Scientists say we cannot allow this to happen. People in power stand in our way.”
The study comes ahead of a United Nations climate summit in Glasgow set to begin October 31. Last month, U.N. Secretary-General António Guterres noted the upcoming event and reminded leaders of wealthy countries that “the world urgently needs a clear and unambiguous commitment to the 1.5-degree goal of the Paris agreement,” and “we are way off track.”
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