Models suggest snowmelt from Greenland and the Arctic is weakening ocean circulation and accelerating warming southward.

The vast network of ocean currents known as the “global ocean conveyor belt” is slowing down. This is a problem because this critical system redistributes heat around the world, influencing both temperature and rainfall.

The Atlantic meridional overturning circulation funnel is important for supplying heat northward through the Atlantic Ocean and controlling climate and marine ecosystems. It is currently weaker than at any time in the past 1,000 years, and global warming may be the culprit. But climate models have struggled to reproduce the changes observed so far.

Our modeling, published in Nature Geoscience, suggests that taking into account meltwater from the Greenland ice sheet and Canadian glaciers could potentially explain the recent weakening of ocean circulation. Masu.

Our results show that a 2°C increase in global warming could make the Atlantic overturning circulation one-third weaker than it was 70 years ago. This will lead to major changes in climate and ecosystems, including accelerated warming in the Southern Hemisphere, harsher winters in Europe, and weakened tropical monsoons in the Northern Hemisphere. Our simulations also show that such changes may occur much sooner than others have expected.

Changes in Atlantic meridional overturning circulation

The Atlantic circulation has been continuously monitored since 2004. However, a long-term perspective is needed to assess potential changes and their causes.

There are many ways to figure out what was happening before these measurements started. One method is based on sediment analysis. These estimates suggest that the Atlantic meridional circulation is the weakest it has been in millennia and has weakened by about 20% since the mid-20th century.

There is evidence that the Earth has already warmed by 1.5 degrees Celsius since the Industrial Revolution.

The rate of warming in the Arctic has nearly quadrupled in recent decades.

Snowmelt weakens ocean circulation patterns

High temperatures are melting Arctic sea ice, glaciers, and the Greenland ice sheet.

Since 2002, Greenland has lost 5.9 trillion tons (gigatons) of ice. To put this into perspective, imagine the entire state of New South Wales is covered in ice 8 meters thick.

This fresh snowmelt water that flows into the subarctic ocean is lighter than salty seawater. Therefore, less water descends into the deep sea. This reduces the southward flow of deep, cold water from the Atlantic Ocean. It also weakens the Gulf Stream, the main path for warm water at the surface to flow back north.

The Gulf Stream gives the UK mild winters compared to other places within the same distance from the North Pole, such as Canada’s St Pierre and Miquelon.

Our new research shows that meltwater from the Greenland ice sheet and Canada’s Arctic glaciers is the missing piece of the climate puzzle.

When we incorporate this into simulations using Earth system models and high-resolution ocean models, we find that the slowdown in ocean circulation reflects reality.

Our study confirms that the Atlantic overturning circulation has slowed since the mid-20th century. It also gives us a glimpse into the future.

Atlantic connectivity

Our new research also shows that the North and South Atlantic Oceans are more connected than previously thought.

The weakening of the overturning circulation over the past few decades has obscured the effects of warming in the North Atlantic, creating what is known as a “warming hole.”

When ocean circulation is active, more heat is transferred to the North Atlantic. However, weakening ocean circulation means that sea surface temperature increases in southern Greenland are much lower than elsewhere.

Reduced transfer of heat and salt to the North Atlantic means more heat and salt accumulates in the South Atlantic. As a result, temperatures and salinity in the South Atlantic rose faster.

Our simulations show that changes in the far North Atlantic will also be felt in the South Atlantic within 20 years. This provides new observational evidence of a slowdown in the Atlantic overturning circulation over the past century.

What will the future hold?

The latest climate projections suggest that the Atlantic overturning circulation will weaken by about 30% by 2060. However, these projections do not take into account the meltwater flowing into the subarctic ocean.

The Greenland ice sheet will continue to melt over the next century, likely raising global sea levels by about 10 centimeters. If this additional snowmelt water is included in climate projections, the overturning circulation will weaken sooner. It could fall by 30% by 2040. This is 20 years earlier than originally predicted.

A rapid decline in such overturning circulations in the coming decades will destroy the climate and ecosystems. A harsher winter is expected in Europe and drier conditions in the northern tropics. In the Southern Hemisphere, including Australia and southern South America, summers are likely to be warmer and rainier.

Our climate has changed dramatically over the past 20 years. Further melting of the ice sheets will accelerate further disruption of the climate system.

This means there is even less time for the climate to stabilize. Therefore, it is imperative that humanity acts to reduce emissions as soon as possible.

This article is republished from The Conversation under a Creative Commons license. Read the original article.