Climate change is slowing the conveyor belts of ocean currents that bring warm water from the tropics to the North Atlantic.
Our study published today (June 6th) Natural climate changeNotice the serious impact on the Earth’s climate if this Atlantic conveyor completely collapses.
We have discovered that the collapse of this system, called the Atlantic meridional overturn, changes the Earth’s climate into a more La Niña-like state.
This means increased rainfall from floods in eastern Australia and worsening seasons for droughts and wildfires in the southwestern United States.
Australians on the east coast know how relentless La Niña feels. Climate change filled our atmosphere with moist air, and the two summers of La Niña warmed the northern waters of Australia.
Both have contributed to some of the wettest conditions we have ever experienced, with record floods in New South Wales and Queensland.
Meanwhile, in southwestern North America, record droughts and severe wildfires put a heavy burden on emergency services and agriculture, and the 2021 fire alone is estimated to cost at least US $ 70 billion.
The Earth’s climate is dynamic, variable, and constantly changing. However, the current trajectory of greenhouse gas emission declines is giving a big kick to the entire system and has uncertain consequences. As a result, the textbook description of the planet’s ocean circulation and its effects will be rewritten.
What is the Atlantic Overturned Meridian Circulation?
The Atlantic Overturn Circulation includes a large flow of warm tropical water to the North Atlantic Ocean, helping to keep the European climate calm while giving the tropical climate the opportunity to lose excess heat. In the Southern Hemisphere, there is an equivalent capsizing of the Southern Ocean.
Climate records dating back 120,000 years reveal that the Atlantic capsizing cycle was turned off or dramatically slowed during the Ice Age.
Switch on the so-called “interglacial”, when the Earth’s climate is warm, to adjust the climate of Europe.
Since the beginning of human civilization about 5,000 years ago, the overthrow of the Atlantic has been relatively stable. But over the last few decades, slowdowns have been detected, which scientists are worried about.
Why slow down? One of the obvious consequences of global warming is the melting of the ice caps of Greenland and the polar regions of Antarctica.
When these ice caps melt, large amounts of freshwater are released into the ocean, making the water more buoyant and reducing dense water subsidence at high latitudes.
In the area around Greenland alone, 5 trillion tons of ice have melted over the last 20 years. This is equivalent to 10,000 Sydney Harbor worth of freshwater.
This melting rate is set to increase over the next few decades if global warming continues unabated.
The collapse of the capsized circulation of the North Atlantic and Antarctica will significantly change the anatomy of the world’s oceans.
It will make them fresher in the depths, deplete them oxygen, and starve the upper seas for the nutrient upwelling provided when the deep sea resurfaces from the depths of the ocean. The impact on the marine ecosystem will be profound.
The melting of Greenland’s ice is already well underway, and scientists say that if greenhouse gas emissions aren’t curtailed, the Atlantic overthrow will be at least the past 1,000 years, with predictions of the future collapse of the Card in the coming centuries. Estimated to be the weakest during.
Effect of deceleration
In our study, we used a comprehensive global model to see what the Earth’s climate would look like under such a collapse.
We switched off Atlantic capsizing by applying a large-scale snowmelt anomaly to the North Atlantic, and then compared this to an equivalent run without snowmelt.
Our focus was to see how the Earth’s climate changes in remote areas far south of Antarctica, beyond the influence of well-known regions around Europe and North America.
The first thing the model simulation revealed was that a large amount of heat accumulated just south of the equator without the Atlantic Ocean capsizing.
This excess tropical Atlantic heat pushes warmer, moist air into the upper troposphere (about 10 km into the atmosphere), causing dry air to fall over the eastern Pacific Ocean.
The descending air strengthens the trade winds and pushes warm water towards the Indonesian sea. And this helps to make the tropical Pacific look like La Niña.
Australians may think of La Niña’s summers as cool and rainy. However, under the long-term warming trend of climate change, their worst impact is the rain from floods, especially in the east.
It also shows that the Atlantic north-south hot salt can be felt south to Antarctica. Warm air rising over the western Pacific causes changes in the wind propagating south to Antarctica. This deepens the atmospheric depression in the Amundsen Sea off the western coast of Antarctica.
This low-pressure system is known to affect not only the melting of ice sheets and ice shelves, but also the circulation of the western sea to the Ross Sea and the spread of sea ice.
New world order
In the history of the Earth, apart from giant meteorites and supervolcanoes, our climate system has never been shaken by changes in atmospheric gas composition as imposed today by the unabated combustion of fossil fuels. ..
The ocean is the flywheel of the Earth’s climate, absorbing large amounts of heat and carbon, slowing the pace of change. But the rewards are the rise in sea levels, the melting of ice, and the significant slowdown in the Atlantic capsizing cycle predicted this century.
It is now known that this slowdown affects not only the North Atlantic region, but also Australia and Antarctica.
Growing a new low-carbon economy can prevent these changes. Doing so will change the history of the Earth’s climate in less than a century. This time we are heading in a better direction.
Matthew England, Professor of Scientists, and Deputy Director of ARC Australia Center for Antarctic Sciences (ACEAS), UNSW Sydney. Andrea S. Tachette, Associate Professor of UNSW Sydney, Brian Olivera Pinto, Candidate of Dr. UNSW Sydney.
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