Q13 – Excess heat in oceans

This question was asked to the public in Sweden, Norway, Finland, Denmark and the UK in the Sustainable Development Misconception Study 2020

In December 2020 Gapminder launches a brand new service for upgrading your worldview, where you will be able to take this (and many other) tests and become certified gapm.io/upgrader


How much of the excess heat from global warming is captured in the oceans?

a) Around 10%

b) Around 50%

c) Around 90%

Correct answer

More than 90% of global warming is captured in oceans.

Don’t look for global warming outside your window

Many of us look for global warming in our local weather but, so far, the weather changes that are caused by climate change are spread unevenly over the planet and you probably haven’t experienced much of it first hand. A lot of heat is actually trapped inside the atmosphere every day, but you can’t detect it by putting your finger in the air, because less than 7% of the excess heat stays in the air. Of the earth’s total surface, 71% is covered by oceans and that’s where 93% of the heat sneaks away. Over the last 50 years, the average temperature in the upper 75 meters of the oceans has increased by half a degree Celsius. That might sound like a small change, but the amount of energy needed to heat up that amount of water would be devastating if it had stayed in the air.

This also means that we should expect a very long delay when we finally manage to reduce the extra greenhouse gasses we emit. When the same amount of heat enters and leaves the atmosphere every day, no excess heat is staying, but we will still be stuck with all the extra heat hiding in the oceans. From that moment it will probably take more than a century for the extra energy in the oceans to eventually escape up into the atmosphere and out into space, where it should be. Not until that has happened can the average air temperature in the air start sinking again.

Data sources

The data behind the trend of warmer oceans is so reliable that the UN Climate Report, IPCC’s Fifth Report[1] call this fact “virtually certain”. Air temperatures are estimated across the world and therefore the energy captured in air can be calculated. Temperatures at different ocean depths have always been trickier to gather. Historic data came mainly from Nansen[3] bottles until the 1950’s when bathythermographs[4] started being used.

During the last 20 years temperatures down to 2000 meters have been measured with small ARGO[2] floats which have covered almost all parts of the oceans since 2005. The ARGO floats sink to 2000 meters depth and then return to the surface to report their measurements. You can see the latest data from almost 4000 of them in real time on the Argovis map[3]. Ship-based stations still dominate when measuring below  2000 meters, but recently the Deep ARGO floats started collecting temperatures all the way down to 6000 meters, in really deep water basins where no historic measurements exist.

Source 1 – IPCC Fifth Assessment Report (page 266)

Source 2 – ARGO

Source 3 – Wikipedia — Nansen Bottles

Source 4 – Wikipedia —  Bathythermographs

Source 5 – Argovis map of floats’ current positions