These last few months have been a turbulent time to be an oceanographer, particularly one specialising in the vast Southern Ocean around Antarctica and its role in our climate. The media has been awash with stories of marine heatwaves across the northern hemisphere, the potential collapse of the Atlantic meridional overturning circulation by mid-century and the record-breaking deficit in Antarctic sea ice emerging this southern winter. Alongside heatwaves and bushfires in North America and southern Europe, flooding in China and South American winter temperatures above 38C, the climate has moved from a “future problem” to a “now problem” in the minds of many.
The global climate is one hugely complex interconnected system. While the Antarctic and Southern Ocean are far removed from our daily lives, they play an oversized role in this system and the future climate that concerns humanity now. “Global warming” is really “ocean warming”. The atmospheric temperature change, the 1.5C Paris target we are now perilously near to exceeding, really is only a few percent of our total excess trapped heat. Almost all the rest is in the ocean and it is around Antarctica that it is predominantly taken up. How this uptake may change in the future as winds, temperatures and ice shift is a critical scientific, and human, question.
This unique exchange between the atmosphere and Southern Ocean is controlled by the combination of extreme cold and freezing at the Antarctic margins and the constant blowing of the roaring 40s, furious 50s and screaming 60s. They act to pump deep old water to the surface and push newly modified water, fresh with observable human fingerprints of heat, meltwater, carbon and oxygen, into the ocean abyss where it may be trapped for centuries or longer. These old deep waters also bring nutrients to the surface; nutrients that are then exported to replenish and sustain the warmer oceans that we fish. However, recent studies from multiple research centres show this overturning has weakened over the past decades and components of it may even collapse in the coming century.
The Southern Ocean is also the driver of almost all the melt of the Antarctic ice sheet. Since 1992 the Antarctic has been losing ice at a rate of around 100bn tonnes per year, driven primarily by warmer deep waters coming into contact with the ice sheet. This melt has driven up global sea levels by about 7mm out of the total 10cm rise since 1992. The proportion that Antarctic melt contributes to this rise is increasing and is projected to raise sea levels to somewhere between two and 10 metres by 2300 under present emission trajectories.
Our inability to confidently predict between an extremely challenging two metres and a civilisation-ending 10 metres of sea level rise is an exemplar of the problem facing Antarctic and Southern Ocean researchers. Without more data and more research, we cannot confidently say whether the Southern Ocean will continue to sweep our warming and CO2 emissions “under the carpet” in the deep ocean, whether we are severely underestimating the scale and speed of sea level rise, or how and when melt may influence the global ocean circulation, gradually or suddenly via a tipping point.
This uncertainty is encapsulated in the ongoing phenomenally low sea ice growth season. There is now 2.5m sq km less sea ice than there should be at this time of year, roughly the size of Western Australia. It is so far outside our observed records that hyperbole has flourished even within the scientific community. Many theories exist for this year’s anomaly, but the question of whether this is climate change finally catching up with the previously robust Antarctic sea ice, as it has in the Arctic, is still unknown at present and will take years to untangle.
These are the pressing questions oceanographers need to answer to chart a course through an uncertain coming century. Hundreds of scientists are meeting this month in Hobart to discuss exactly how we should do this. The Southern Ocean Observing System, a coalition of scientists from across the world, is holding its first ever global conference on the Southern Ocean in a changing world.
The call arising from this gathering of experts will inevitably be that we need more and new observations of the Southern Ocean and Antarctic, especially in the winter and under the ice, where there is presently almost no data.
It will say we need to improve our understanding of ice and ocean processes and incorporate these into new and better models, and it will also say that we need more coordination between nations, such as the Ocean:Ice project, to cover the vast and complex wilderness of the Southern Ocean and Antarctic.
All of this is achievable, but the need for sustained research and investment in Southern Ocean and Antarctic science, along with its underpinning infrastructure and technology for our future has never been more pressing than now.
Andrew Meijers is a physical oceanographer at the British Antarctic Survey. He leads the UK component of the Horizon Europe Ocean:Ice project, a multination consortium seeking to understand the linkages between the Southern Ocean, Antarctic ice sheet and global climate
