Oceans slow global warming. How?

Article by Isabel Key and Mina Frost.

The oceans regulate and stabilize the global climate, through holding both CO2 and heat [1,4,5]. In fact, they have stored around 90% of the heat trapped by greenhouse gases since 1955 [4]! Most of the remaining 10% of heat energy goes into warming the land and melting ice, with only very little causing warming of the atmosphere itself [4]. The oceans can take up so much heat for three reasons:

1) Oceans are big and deep, covering 71% of the Earth’s surface with an average depth of 4km [4].

2) Water has a high “heat capacity”: warming water by 1°C takes much more heat energy than warming the same volume of air by 1°C [4].

3) Water is dynamic, with currents and waves distributing heat throughout the ocean [4].

What about CO2? So far, oceans have taken up around 30% of human CO2 emissions [1]. Ocean CO2 uptake occurs by both the “solubility pump” and the “biological pump”[2,7]. We’ll explain. Don’t worry:

The solubility pump involves CO2 being taken up directly by seawater – the CO2 “dissolves” [7]. This does not permanently store the carbon [2], but most of the CO2 reacts to form new substances which cannot easily re-enter the atmosphere [1].

The biological pump stores carbon more permanently [2]. It involves phytoplankton using photosynthesis to turn CO2 into oxygen and organic matter, allowing them to grow [6]. The phytoplankton are eaten by animals, such as krill, which then poop out the carbon in pellets which sink to the bottom of the ocean [2,3]. This process transfers CO2 from the atmosphere down to the deep sea, where the poop and remains of animals are buried [3], storing carbon for thousands of years [2].

It’s thought that the oceans will eventually naturally take up over 80% of CO2 emissions from humans [1]. The movement of CO2 into the ocean is a slow process, however, and is not fast enough to prevent CO2 from building up in the atmosphere in the next few decades [1]. Although this process does slow global warming, it also causes ocean acidification [1] – more on that in another post.

So, without the oceans the planet would have warmed a lot quicker [7]! The next time you swim in the sea, say thank you!


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