Climate change: Atlantic Ocean is headed for a tipping point, says new study

This article was authored by Rene van Westen, Henk A Dijkstra, and Michael Kliph, and revealed in The Conversation

Superstorms, abrupt local weather shifts and New York City frozen in ice. That’s how the blockbuster Hollywood film The Day After Tomorrow depicted an abrupt shutdown of the Atlantic Ocean’s circulation and the catastrophic penalties.

While Hollywood’s imaginative and prescient was excessive, the 2004 film raised a critical query: If international warming shuts down the Atlantic Meridional Overturning Circulation, which is essential for carrying warmth from the tropics to the northern latitudes, how abrupt and extreme would the local weather modifications be?

Twenty years after the film’s launch, we all know a lot extra concerning the Atlantic Ocean’s circulation. Instruments deployed within the ocean beginning in 2004 present that the Atlantic Ocean circulation has observably slowed over the previous twenty years, probably to its weakest state in virtually a millennium.

Studies additionally counsel that the circulation has reached a harmful tipping level prior to now that despatched it into a precipitous, unstoppable decline, and that it might hit that tipping level once more because the planet warms and glaciers and ice sheets soften.

In a new study utilizing the newest era of Earth’s local weather fashions, we simulated the move of contemporary water till the ocean circulation reached that tipping level.

The outcomes confirmed that the circulation might totally shut down inside a century of hitting the tipping level, and that it’s headed in that course. If that occurred, common temperatures would drop by a number of levels in North America, components of Asia and Europe, and folks would see extreme and cascading penalties all over the world.

We additionally found a physics-based early warning sign that may alert the world when the Atlantic Ocean circulation is nearing its tipping level.

The ocean’s conveyor belt

Ocean currents are pushed by winds, tides and water density variations.

In the Atlantic Ocean circulation, the comparatively heat and salty floor water close to the equator flows in direction of Greenland. During its journey, it crosses the Caribbean Sea, loops up into the Gulf of Mexico, after which flows alongside the US East Coast earlier than crossing the Atlantic.

This present, often known as the Gulf Stream, brings warmth to Europe. As it flows northward and cools, the water mass turns into heavier. By the time it reaches Greenland, it begins to sink and move southward. The sinking of water close to Greenland pulls water from elsewhere within the Atlantic Ocean and the cycle repeats, like a conveyor belt.

Too a lot contemporary water from melting glaciers and the Greenland ice sheet can dilute the saltiness of the water, stopping it from sinking, and weaken this ocean conveyor belt.

A weaker conveyor belt transports much less warmth northwards and likewise allows much less heavy water to achieve Greenland, which additional weakens the conveyor belt’s energy. Once it reaches the tipping level, it shuts down rapidly.

What occurs to the local weather on the tipping level?

The existence of a tipping level was first observed in an excessively simplified mannequin of the Atlantic Ocean circulation within the early Sixties. Today’s extra detailed local weather fashions point out a continued slowing of the conveyor belt’s energy underneath local weather change. However, an abrupt shutdown of the Atlantic Ocean circulation seemed to be absent in these local weather fashions.

This is the place our study is available in. We carried out an experiment with a detailed local weather mannequin to search out the tipping level for an abrupt shutdown by slowly rising the enter of contemporary water.

We discovered that after it reaches the tipping level, the conveyor belt shuts down inside 100 years. The warmth transport in direction of the north is strongly lowered, resulting in abrupt local weather shifts.

The outcome: Dangerous chilly within the North

Regions which might be influenced by the Gulf Stream obtain considerably much less warmth when the circulation stops. This cools the North American and European continents by a few levels.

The European local weather is rather more influenced by the Gulf Stream than different areas. In our experiment, that meant components of the continent warmed at greater than 5 levels Fahrenheit (3 levels Celsius) per decade — far quicker than as we speak’s international warming of about 0.36 F (0.2 C) per decade.

We discovered that components of Norway would expertise temperature drops of greater than 36 F (20 C). On the opposite hand, areas within the Southern Hemisphere would heat by a few levels.

These temperature modifications develop over about 100 years. That may seem to be a very long time, however on typical local weather time scales, it is abrupt.

The conveyor belt shutting down would additionally have an effect on sea stage and precipitation patterns, which might push different ecosystems nearer to their tipping factors. For instance, the Amazon rainforest is weak to declining precipitation. If its forest ecosystem turned to grassland, the transition would launch carbon to the ambiance and outcome within the lack of a helpful carbon sink, additional accelerating local weather change.

The Atlantic circulation has slowed considerably within the distant previous. During glacial durations when ice sheets that coated giant components of the planet had been melting, the inflow of contemporary water slowed the Atlantic circulation, triggering big local weather fluctuations.

So, when will we see this tipping level?

The large query — when will the Atlantic circulation attain a tipping level? — stays unanswered. Observations don’t return far sufficient to supply a clear outcome. While a current study recommended that the conveyor belt is quickly approaching its tipping level, probably inside a few years, these statistical analyses made a number of assumptions that give rise to uncertainty.

Instead, we had been in a position to develop a physics-based and observable early warning sign involving the salinity transport on the southern boundary of the Atlantic Ocean. Once a threshold is reached, the tipping level is more likely to observe in a single to 4 many years.

The local weather impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea stage and precipitation modifications will severely have an effect on society, and the local weather shifts are unstoppable on human time scales.

It may appear counterintuitive to fret about excessive chilly because the planet warms, but when the primary Atlantic Ocean circulation shuts down from an excessive amount of meltwater pouring in, that’s the chance forward.