Just One Ocean Is Absorbing Nearly All The Excess Heat. The Effects May Be Profound

Over the last 50 years, the oceans have absorbed about 40 percent of our carbon dioxide emissions and 90 percent of the excess heat in the atmosphere.

Our research shows that some oceans work harder than others.

We looked at how ocean warming has played out over the last 50 years using a computer model.

The Southern Ocean dominates the global absorption of heat.

The rate of climate change is controlled by the Southern Ocean heat absorption.

It takes thousands of years for heat trapped in the ocean to be released back into the atmosphere, which is why this Southern Ocean warming is irreversible.

If we don't achieve net zero and stop carbon dioxide emissions, the changes happening now will only get worse.

It's important yet difficult to measure ocean heating

Climate change can be mitigated by ocean warming, but it costs. Sea levels are rising because of warm weather. Extreme weather events are becoming more frequent and the heat stress in the marine environment is increasing.

We don't know much about ocean warming. There are three reasons for this.

Tracking temperature changes at the ocean surface and in the atmosphere is the first step. It is difficult to know where the heat is coming from.

We don't have a way to track the ocean's temperature. We don't have a lot of observations in the deep ocean and under sea ice.

Observations don't go back very far in time. Prior to the 1990s, there was no reliable data from 700 meters deep.

Our modeling approach

Prior to any significant human-caused climate change, we ran an ocean model with atmospheric conditions that were stuck in the 1960's.

Each ocean basin was allowed to move forward in time and experience climate change, while the rest of the basin was held back.

We looked at how much each factor contributes to the observed ocean warming.

The Southern Ocean only covers 15 percent of the ocean's surface area, but it is the most important absorber of this heat.

The Southern Ocean alone could account for almost all of the global ocean heat gain.

There is a significant impact on the ecology of the Southern Ocean. The krill's habitat contracts when the ocean warms and they move further south.

As a key component of the food web, this will change the distribution and population of larger predator fish, such as tooth and ice fish. It will make penguins and whales even more stressed.

So why is the Southern Ocean absorbing so much heat?

The geographical set-up of the region, with strong westerly winds surrounding Antarctica, exert their influence over an ocean that is unaffected by land mass.

The Southern Ocean winds bring cold water to the surface over a long period of time.

The cold water is pushed northward, absorbing vast amounts of heat from the warmer atmosphere, before the excess heat is pumped into the ocean's interior.

Our greenhouse gas emissions and wind-driven circulation help to get heat into the ocean interior.

We can explain almost all of the global ocean heat gain when we combine the warming and wind effects only over the Southern Ocean.

The other ocean basins are still warming.

Over the past 50 years, changes in total ocean heat content have been driven by the huge heat absorption in the Southern Ocean.

We have much to learn

While this discovery sheds new light on the Southern Ocean as a key driver of global ocean warming, we still have a lot to learn.

Projections show that the ocean will be even warmer in the future.

The Southern Ocean could see its heat content increase by as much as seven times if it continues to account for most of the ocean heat.

Changes in the ocean conveyor belt, rapid melting of ice shelves, and further disruptions to the Southern Ocean food web are just some of the things that will be impacted by this.

We need to keep expanding our observations in the Southern Ocean in order to capture all of the changes.

One of the most important new data streams will be new ocean floats that can measure deeper ocean temperatures, as well as small temperature sensors on elephant seals, which give us essential data of ocean conditions in winter.

The less carbon dioxide we emit, the less ocean change will occur. Billions of people live near the coast and this will limit the disruption of their lives.

Matthew England is the deputy director of the Australian Centre for excellence in Antarctic Science and Maurice Huguenin is a PhD candidate.

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