‘A Little Shocking’: Ocean Currents Are Speeding up Significantly, Study Finds

The world's oceans are moving faster, and researchers think it might be another sign of the climate crisis.
A new paper, published in Science Advances Wednesday, found that 76 percent of the top 2,000 meters of the ocean appears to have sped up since the 1990s, largely because of wind speeds. And the ocean's speedup is more than can be explained by "natural variability."
"The Earth is our patient, and you look for symptoms of how it is reacting to anthropogenic greenhouse gas forcing," study coauthor and National Oceanic and Atmospheric Administration researcher Michael McPhaden told The Washington Post. "This is another symptom."
Each ocean current moves as much water as all the world's rivers combined, Science Magazine explained. Researchers found that between 1990 and 2013, the energy of these currents increased by 15 percent per decade.
"This is a really huge increase," Susan Wijffels, an oceanographer at the Woods Hole Oceanographic Institution who was not involved with the paper, told Science Magazine.
At the same time, wind speed has increased by around two percent per decade and ocean current speed by around five percent per decade, according to The Washington Post.
Up until now, scientists have been unsure of how the climate crisis would impact ocean currents. Some models suggested a warmer world would lead to a slower ocean, The Scientist explained. This is certainly the case for the Atlantic Meridional Overturning Circulation (AMOC) in the North Atlantic, but because this current is driven by cold water sinking and flowing southward, its slowing doesn't negate the possibility that winds could increase other currents, The Washington Post explained.
Some climate models had shown that global warming would lead to greater wind speeds, but not until around 2100 after temperatures had increased substantially. The fact that it is happening now could mean that the Earth is more sensitive to warming than the models have shown, McPhaden told The Washington Post.
While researchers can't say for certain what is driving the increased circulation speed, their findings are likely to spark more research into the issue.
"This is quite an exciting paper," Joellen Russell, a University of Arizona geoscientist who was not involved in the study, told The Scientist. "I think the results are robust, I think they're important, and I think they are a little shocking."
Study coauthor Shijian Hu of the Chinese Academy of Sciences's Institute of Oceanology told The Scientist that there was not a lot known about how ocean circulation was behaving in the context of climate change because of a lack of direct observation of the ocean.
To overcome this lack, Hu's team looked at five different reanalyses, which combine observations with models to fill in for missing data points, as Science Magazine explained. When all five turned up an increase in ocean energy after 1990, the researchers then turned to real-time data from the Argo system of floats for confirmation:
A look at data from the Argo array, a fleet of nearly 4000 robotic floats deployed around the world, provided the best test. The floats have been bobbing up and down in the ocean's uppermost 2000 meters for the past 15 years, measuring temperature and salinity. They don't track velocity through the water column. But their data do indicate where winds have piled up water, helping create differences in pressure that drive large-scale flows. By combining those data with the floats' own current-borne trajectories, investigators can reconstruct overall currents and their speed.
The data set, compiled by oceanographer Alison Gray of the University of Washington, Seattle, covers only 6 years, from 2005 to 2010, but Hu found that it reveals an even clearer global speedup than the reanalysis models. "The evidence in the Argo data is absolutely astonishing," says Eleanor Frajka-Williams, an oceanographer at the United Kingdom's National Oceanography Centre, who was not part of the study.
So what does a faster ocean actually mean? The study didn't look at localized effects, but researchers can point to some likely outcomes.
One is that a more turbulent ocean could actually absorb more heat from the atmosphere, MIT oceanographer and climatologist Gael Forget told The Scientist.
Another is that it could change how and where heat is circulated.
"Perhaps the most important consequence is the increased redistribution of heat around the planet that stronger circulation would bring," Alex Sen Gupta, an ocean and climate expert at the University of New South Wales in Sydney who was not involved with the research, told The Washington Post. "This would affect temperature distributions and could affect weather patterns — but more work would be needed to make these links."
Shifting water temperatures would also impact marine life. For example, the East Australian Current has gotten stronger and brought warmer waters to the Tasmanian coast, where they are wilting the area's kelp forests.
But the net effect of increased circulation is not necessarily good or bad.
"There are always winners and losers in these situations," Russel told The Scientist.
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The speed and scale of the response to COVID-19 by governments, businesses and individuals seems to provide hope that we can react to the climate change crisis in a similarly decisive manner - but history tells us that humans do not react to slow-moving and distant threats.
A Game of Jenga
<p>Think of it as a game of Jenga and the planet's climate system as the tower. For generations, we have been slowly removing blocks. But at some point, we will remove a pivotal block, such as the collapse of one of the major global ocean circulation systems, for example the Atlantic Meridional Overturning Circulation (AMOC), that will cause all or part of the global climate system to fall into a planetary emergency.</p><p>But worse still, it could cause runaway damage: Where the tipping points form a domino-like cascade, where breaching one triggers breaches of others, creating an unstoppable shift to a radically and swiftly changing climate.</p><p>One of the most concerning tipping points is mass methane release. Methane can be found in deep freeze storage within permafrost and at the bottom of the deepest oceans in the form of methane hydrates. But rising sea and air temperatures are beginning to thaw these stores of methane.</p><p>This would release a powerful greenhouse gas into the atmosphere, 30-times more potent than carbon dioxide as a global warming agent. This would drastically increase temperatures and rush us towards the breach of other tipping points.</p><p>This could include the acceleration of ice thaw on all three of the globe's large, land-based ice sheets – Greenland, West Antarctica and the Wilkes Basin in East Antarctica. The potential collapse of the West Antarctic ice sheet is seen as a key tipping point, as its loss could eventually <a href="https://science.sciencemag.org/content/324/5929/901" target="_blank">raise global sea levels by 3.3 meters</a> with important regional variations.</p><p>More than that, we would be on the irreversible path to full land-ice melt, causing sea levels to rise by up to 30 meters, roughly at the rate of two meters per century, or maybe faster. Just look at the raised beaches around the world, at the last high stand of global sea level, at the end of the Pleistocene period around 120,0000 years ago, to see the evidence of such a warm world, which was just 2°C warmer than the present day.</p>Cutting Off Circulation
<p>As well as devastating low-lying and coastal areas around the world, melting polar ice could set off another tipping point: a disablement to the AMOC.</p><p>This circulation system drives a northward flow of warm, salty water on the upper layers of the ocean from the tropics to the northeast Atlantic region, and a southward flow of cold water deep in the ocean.</p><p>The ocean conveyor belt has a major effect on the climate, seasonal cycles and temperature in western and northern Europe. It means the region is warmer than other areas of similar latitude.</p><p>But melting ice from the Greenland ice sheet could threaten the AMOC system. It would dilute the salty sea water in the north Atlantic, making the water lighter and less able or unable to sink. This would slow the engine that drives this ocean circulation.</p><p><a href="https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century" target="_blank">Recent research</a> suggests the AMOC has already weakened by around 15% since the middle of the 20th century. If this continues, it could have a major impact on the climate of the northern hemisphere, but particularly Europe. It may even lead to the <a href="https://ore.exeter.ac.uk/repository/handle/10871/39731?show=full" target="_blank" rel="noopener noreferrer">cessation of arable farming</a> in the UK, for instance.</p><p>It may also reduce rainfall over the Amazon basin, impact the monsoon systems in Asia and, by bringing warm waters into the Southern Ocean, further destabilize ice in Antarctica and accelerate global sea level rise.</p>The Atlantic Meridional Overturning Circulation has a major effect on the climate. Praetorius (2018)
Is it Time to Declare a Climate Emergency?
<p>At what stage, and at what rise in global temperatures, will these tipping points be reached? No one is entirely sure. It may take centuries, millennia or it could be imminent.</p><p>But as COVID-19 taught us, we need to prepare for the expected. We were aware of the risk of a pandemic. We also knew that we were not sufficiently prepared. But we didn't act in a meaningful manner. Thankfully, we have been able to fast-track the production of vaccines to combat COVID-19. But there is no vaccine for climate change once we have passed these tipping points.</p><p><a href="https://www.weforum.org/reports/the-global-risks-report-2021" target="_blank">We need to act now on our climate</a>. Act like these tipping points are imminent. And stop thinking of climate change as a slow-moving, long-term threat that enables us to kick the problem down the road and let future generations deal with it. We must take immediate action to reduce global warming and fulfill our commitments to the <a href="https://www.ipcc.ch/sr15/" target="_blank" rel="noopener noreferrer">Paris Agreement</a>, and build resilience with these tipping points in mind.</p><p>We need to plan now to mitigate greenhouse gas emissions, but we also need to plan for the impacts, such as the ability to feed everyone on the planet, develop plans to manage flood risk, as well as manage the social and geopolitical impacts of human migrations that will be a consequence of fight or flight decisions.</p><p>Breaching these tipping points would be cataclysmic and potentially far more devastating than COVID-19. Some may not enjoy hearing these messages, or consider them to be in the realm of science fiction. But if it injects a sense of urgency to make us respond to climate change like we have done to the pandemic, then we must talk more about what has happened before and will happen again.</p><p>Otherwise we will continue playing Jenga with our planet. And ultimately, there will only be one loser – us.</p>By John R. Platt
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