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

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 may affect how the oceans absorb and store carbon. This includes the possibility that, as anthropogenic (manmade) CO2 emissions continue, some of the ocean carbon sequestration routes could change from being sink to a source in the future.