More than half of the world’s oceans are already affected by climate change

More than 50% of the world’s oceans could already be affected by climate change, with that figure rising to 80% over the next few decades, a new study has shown.

Scientists used climate models and observations in deeper areas of the ocean around the world to calculate for the first time the point at which changes in temperature and salt levels – good indicators of the impact of changes man-induced climatic conditions – would control natural variations.

The study, published in Nature’s climate change, estimates that 20-55% of the Atlantic, Pacific and Indian Oceans now have significantly different temperatures and salt levels, while they will increase to 40-60% by mid-century and 55-80% d ‘by 2080.

He also revealed that the oceans of the southern hemisphere are more rapidly affected by climate change than the northern hemisphere, changes being detectable there since the 1980s.

Professor Eric Guilyardi, co-author at the University of Reading and LOCEAN-IPSL, Laboratory of Oceanography and Climate in Paris, said: “We have been detecting changes in ocean surface temperatures due to climate change since decades now, but changes in large areas of the ocean, especially deeper parts, are much more difficult to detect. “

Yona Silvy, PhD student at LOCEAN-IPSL / Sorbonne University, and lead author of the study, said: “We wanted to know if the temperature and salt levels were high enough to overcome the natural variability in these deeper areas, c ‘that is if they had risen or fallen higher than they ever would during normal peaks and troughs, which affects global ocean circulation, sea level rise and poses a threat to human societies and ecosystems.

Previous studies have measured the impact of climate change on the ocean by examining surface temperatures, precipitation and sea level rise, but few have looked at regional effects deeper in the ocean to obtain an more complete picture.

The effects of climate change are more difficult to detect in the deeper, more isolated parts of the ocean, where heat and salt travel at a slower rate due to weaker mixing processes. It is also difficult in poorly observed areas or where natural variability is high.

Yona Silvy and her co-authors used model simulations with and without the impact of human activity and analysis that combines both temperature and ocean salt to detect significant changes and when they occurred. probable detection, also known as “time of emergence”. Yet these are regions that will be remembered by these changes for decades, if not centuries.

The detectable changes above the natural variability were calculated to be observed in the oceans of the Northern Hemisphere between 2010 and 2030, meaning that increases or decreases in temperature and salt levels have likely already had location.

The faster and earlier changes observed in the southern hemisphere underscore the importance of the Southern Ocean for global heat and carbon storage, as surface waters more easily flow to the deeper ocean. However, this part of the world is also particularly poorly observed and sampled, meaning that changes are unlikely to be detected for much longer.

Scientists say better ocean observation and greater investment in ocean modeling are needed to monitor the magnitude of the impact of climate change on the world’s oceans and more accurately predict the larger effect than that. could have on the planet.