How is climate change affecting the oceans and what are the impacts for people?

Bleached coral. Photo: Vardhan Patankar, Wikimedia

The world’s oceans form a primary component of the climate system. They contribute to climate regulation by absorbing carbon dioxide (CO2) emissions and heat. They have absorbed over a quarter of human-caused CO2 and around 90% of the excess heat produced in recent decades. The oceans are by far the largest active carbon reservoir on the planet, storing about 38,000 billion tonnes of carbon. They are also a crucial source of food supply and livelihoods for billions of people.

However, climate change is causing the oceans to warm and become more acidic, which in turn is may affect how the oceans absorb and store carbon. This includes the possibility that, as anthropogenic COemissions continue, some of the ocean carbon sequestration routes could change from a being sink to a source in the future.

Ocean warming, melting ice and sea-level rise

The excess heat taken up by the oceans has increased their mean temperature at an average rate of 0.11°C per decade since 1970. Because the oceans redistribute heat towards the poles, this warming is contributing to the melting of ice sheets and glaciers and leading to a rise in the mean sea level – currently estimated at 0.19m between 1901 and 2010. The greatest threat of future sea level rise comes from the possibility that the massive ice sheets in the Antarctic and Greenland could melt. Sea level rise is also caused by thermal expansion, whereby seawater becomes less dense and expands as it warms, and in recent decades this has been one of the major drivers in this change – responsible for over one-third of all sea level rise observed.

The London School of Economics and Political Science, 28 February 2023. Full article.

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