Over the last 50 years, the oceans have been working hard to slow global warming, absorbing 40% of our carbon dioxide emissions and more than 90% 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 deep in the ocean to be released back into the atmosphere.
If we don't achieve net zero and stop carbon dioxide emissions, the changes happening now will only get worse.
Climate change can be mitigated by ocean warming. 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 wasn't reliable data from 700 metres deep.
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.
To see how much each factor contributes to the observed ocean warming, we separated out the effects of atmospheric warming and surface wind driven changes.
Even though only 15% of the ocean's surface area is covered by the Southern Ocean, it is still 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. When the ocean warms, the krill's habitat contracts 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.
The geographic setup of the region has a lot to do with the influence of the westerly winds over the ocean.
The Southern Ocean winds bring cold water to the surface over a long period of time. The cold water is pushed northward, readily absorbing vast amounts of heat from the warmer atmosphere, before the excess heat is pumped into the ocean's interior around 45-55S.
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.
That doesn't mean the other ocean basins aren't warming. Over the past 50 years, changes in total ocean heat content have been driven by the huge heat absorption in the Southern Ocean.
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.
Alterations to the Southern Ocean food web, rapid melting of ice shelves and changes in the ocean conveyor belt are just some of the things that will be impacted by this.
We need to keep expanding our observations in the Southern Ocean 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.
The article was first published in the Conversation. Maurice is a PhD candidate. Matthew England is a professor at the University of New South Wales. He is a research fellow at the university.
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