Climate change has led to hotter seas across the world: in 2018 European water temperatures reached record levels, and a marine heatwave in the north-east Pacific devastated marine life.

Less predictably, global heating has made the oceans more stable, with discrete, stratified layers that resist mixing. And that could be very bad news, because it could make the blue water that covers 70% of the planet less effective at absorbing atmospheric heat and thus mitigating climate change.

And ever-warmer sea temperatures could have another unwelcome impact: as temperatures rise, levels of dissolved oxygen fall. And that could make it difficult for some sea creatures to breathe.

The oceans play a vital role in the water, energy and carbon cycles upon which all life depends. In 2010, demographers counted 1.9 billion people living within 100kms of the sea and less than 100 metres above sea level: that is 28% of all humanity. Many of them are crowded into 17 megacities with populations of more than 5 million people each. For many, the sea is the neighbourhood.

European researchers warn, in a new and detailed report on the state of the oceans from 1993 to 2010, that the rise in sea temperatures in the Mediterranean is without precedent, and the largest rise of all has been measured in the Arctic Ocean.

They also call as a matter of urgency for comprehensive and systematic monitoring of the ocean. “Human society has always been dependent on the seas,” they warn. “Failure to reach good environmental status for our seas and oceans is not an option.”

Read the full article about climate change and warmer seas by Tim Radford at Climate News Network.