Ocean currents are slowing down as a result of climate change

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Well, new research shows that Earth’s great ocean currents are slowing down, and while the consequences won’t be as immediate or dramatic as in Hollywood fiction, there are real consequences for global weather patterns and sea levels.

“This has essentially been predicted for decades that this circulation would weaken in response to global warming. And now we have the strongest evidence that this is already happening,” said Stefan Rahmstorf of the University of Potsdam who contributed to this study. .

The Atlantic Meridional Overturning Circulation (AMOC) transports water across the planet’s oceans, including the Atlantic, Pacific, and Indian Oceans. The region contributing to the slowdown is the North Atlantic, according to the study.

“ The idea (of this movie), which is actually correct, is that if this overthrowing circulation of the Atlantic gets completely destroyed, it will lead to a strong cooling around the North Atlantic, especially in Europe, to the kind of coastal areas. (from) Great Britain and Scandinavia. But that’s only true if the tilt fails all together, ”said Rahmstorf.

Atlantic Meridional Ocean Circulation Map
In this part of the ocean, Greenland’s ice sheets are melting, contributing to both a rise in sea level and a reduction in the speed of circulation.

“This indicates that the slowdown is likely not a natural change, but the result of human influence. The AMOC has a profound impact on the global climate, and particularly in North America and Europe, so this is evidence of a continued weakening of the global environment. circulatory system is critical evidence for the interpretation of future projections of regional and global climate, ”said Andrew Meijers, deputy scientific leader of the polar oceans at the British Antarctic Survey.

Melting ice in Greenland and heavy rains over the North Atlantic Ocean due to climate change have affected the salinity and density of the waters, Rahmstorf explained.

“Surface warming as well as increased water cycle, increased rainfall and ice melt are all a result of global warming,” in parts of the North Atlantic, he said.

While warm water flows go north, they usually return south as it gets cooler and heavier. Added fresh water from the melting ice slows down this turn due to reduced salinity.

The current deviations of the seawater temperature from normal indicate the cold pool in parts of the North Atlantic Ocean. The arrows represent the general Atlantean meridional wrap-around circulation.
“This weakening also creates cold in the North Atlantic, but it is limited to the ocean. This cold blob, as we call it, is above the ocean and does not touch land,” Rahmstorf said. Current estimates show that this attenuation is moderate, about 15% weaker than normal, and based on data analyzed up to 1,600 years ago.
This color-coded map shows a progression of changing surface temperature anomalies on Earth. Normal temperatures are the average over the base 30-year period from 1951 to 1980. Higher than normal temperatures are shown in red and lower than normal temperatures in blue. The image shows the five-year global temperature anomalies from 2016 to 2020. The scale is in degrees Celsius.

US East Coast to see higher sea levels

One of the main effects of the slowing ocean circulation is on sea levels, especially that of the east coast of the US.

“The north surface current of the AMOC causes water masses to deflect to the right away from the east coast of the US. This is due to the Earth’s rotation diverting moving objects such as currents to the right in the Northern Hemisphere and to the left. in the Southern Hemisphere. As the current slows down, this effect weakens and more water can accumulate on the east coast of the US, leading to increased sea level rise, “said Levke Caesar, one of the authors of the report.

Sea levels are already rising due to factors such as melting ice sheets and warming oceans. According to the National Oceanic and Atmospheric Administration (NOAA), water levels have risen an average of 8 to 9 inches over the past 140 years.

The rate at which these waters rise has also increased in recent years.

“The rate of global sea level rise more than doubled from 1.4mm per year for most of the twentieth century to 3.6mm per year between 2006 and 2015,” said NOAA.

A further slowdown in global ocean circulation, especially along the crucial Gulf Stream off the US East Coast, could be combined with already accelerating sea level rise to make major Northeastern cities even more vulnerable to flooding.

Hotter heat waves, stronger hurricanes

Global weather patterns are critically linked to the oceanic circulations and their transport of heat and nutrients around the planet.
An increase in heat waves across Europe and stronger hurricanes closer to the U.S. coastline as warmer water drifts closer to the coast could be linked to ocean circulation, Rahmstorf said.

“The world’s seven hottest years have all occurred since 2014, with 10 of the hottest years since 2005,” NOAA said. Heat waves are already more common.

The ocean and currents also play a role in absorbing carbon dioxide, the most dominant greenhouse gas, from the atmosphere. The changing currents could reduce the amount of carbon being extracted from the atmosphere, according to NASA.

In addition to affecting humans, the marine biology population is also at risk.

Marine organisms “depend very much on these ocean currents, which basically set the conditions for the entire ecosystem in terms of nutrient supply, temperature and salinity,” Rahmstorf said.

When asked if the AMOC could slow further or even stop, Rahmstorf said climate models suggest the flow will slow to between 34% and 45% by 2100.

Despite a lot of research on this over the past decade, it’s very difficult to quantitatively determine how far away this tipping point is. But the kind of model simulations I know of suggest that if you weaken this circulation by about half, you’re going to get into a critical condition. And so this may very well … be happening by the end of the century, “Rahmstorf said.

“We must (strive to) stay well away from that tipping point because the consequences would be dramatic if the circulatory system broke down completely.”

Hollywood has shown us this possible worst-case scenario of climate change. And while the consequences shown in “The Day After Tomorrow” are highly unlikely, they do illustrate how runaway effects of climate change can result if we don’t heed the warnings of climate scientists.

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