large heat capacity of water, the ocean has an incredible ability to buffer the atmospheric temperatures of planet earth. It is estimated that around ninety percent of the excess heat trapped by greenhouse gas emissions is absorbed by the ocean¹.
The IPPC has estimated that since 1955, “over 90% of the excess heat trapped by greenhouse gases had been stored in the oceans”. After reading that you may be thinking that only 10% of the excess heat has been used to warm the atmosphere, not so bad, right? Wrong! Most of this 10% actually goes towards melting sea ice, ice caps, and glaciers, and warming continental land masses. Only a tiny fraction actually directly warms the atmosphere. This is scary because the ocean’s heat storage ability is finite – there will come a point in time where it is no longer able to keep up with the demands of humanity.
There are a number of reasons why the ocean is able to absorb so much heat. These include²:
- The high heat capacity of water. One litre of water is able to absorb much more heat than the same volume of air, or almost any other substance.
- The ocean is deep, and contains a huge volume of water. 71% of the earth’s surface is covered by ocean, which has an average depth of 4 kilometres.
- Probably the main reason is that the ocean is dynamic – it is always moving due to currents, wind eddies, and other circulation methods. This allows mixing and exchange of the heat throughout the ocean, rather than concentrating on just the surface waters.
Researchers around the world are beginning to realise the importance of the ocean to world climate systems, and are therefore focusing their research like never before. Satellites orbit the globe, continually gathering data for analysis, while scientists work frantically to try and determine if and when the ocean will have absorbed as much heat as it can.
How long can this mechanism continue to work successfully for?
While the world’s oceans are warming at an ever increasing rate³, this obviously can’t continue forever. There will come a point when the ocean can no longer absorb the necessary amount of heat, which will lead to a rapid rise in atmospheric temperatures. The current rate of ocean heat accumulation is “the equivalent of five Hiroshima bombs exploding every second since 1990¹”.
According to scientists, the ocean may begin to release some if its absorbed thermal energy in the near future, if it isn’t doing so already. Various oceanic cycles, which change with a relatively predictable time frame, will probably cause the release of some of the oceans stored heat when they change. Some, like the Interdecadal Pacific Oscillation, are due to change at any time, while others are likely to follow in the coming years¹.
It is obvious therefore that we cannot continue to rely on the ocean as a climate buffer. It will stop absorbing heat as it currently is, and perhaps will even begin to release thermal energy in the near future. We must instead tackle the root of the problem – reducing greenhouse gas emissions – immediately and with full force.
How does the ocean indirectly buffer the atmospheric temperature?
Not only does the ocean absorb atmospheric heat directly, but it also helps reduce the atmospheric greenhouse gas levels. CO2 and other greenhouse gases are easily able to dissolve in water, and therefore in the ocean. By keeping the greenhouse gas concentration lower, the effects of global warming are slowed².
Every year human activity causes the release of around 36 billion tons of CO2, not to mention other greenhouse gases such as methane and nitrates. This has caused atmospheric CO2 concentrations to increase by around 50% since the industrial revolution – from 280ppm to around 400ppm². It has been estimated that the ocean absorbs around 30% of mankind’s CO2 emissions almost immediately, and up to 85% in the long term⁴.
At least 530 billion tons of CO2 has been dissolved in the ocean since the industrial revolution, which is a massive number⁴. If the ocean wasn’t able to dissolve this gas, it would remain in the atmosphere, pushing CO2 concentrations towards 500, 600, or even 700ppm. This would translate to huge rises in global temperature, which would destroy the world as we know it. We need to protect the oceans, not only for their beauty and incredible biodiversity, but also for the indispensable role they play in regulating the earth’s climates.