Europe and Central Asia
5 Nov 2015

Climate change's double whammy: Why we should be more worried about our oceans

The ability of oceans to regulate the Earth's temperature is being compromised. Photo © Craig Jones
By Bruna Campos

We all know the danger humans face from seas and oceans due to climate change. The melting of polar ice caps is causing a rise in sea levels that could submerge coastal communities and islands, and extreme events like storms are becoming more common. But we’re missing another danger: oceans play a crucial role in climate regulation, and rising temperatures threaten to destroy this balance.

How oceans keep the temperature just right

Oceans help to heat the planet by absorbing the sun’s radiation. Through evaporation, the oceans distribute heat around the globe, increasing the temperature and humidity of the air to create rain. Currents help to counteract the uneven distribution of heat by transporting warm and cold water and precipitation from the poles to the equator and back. Oceans also regulate greenhouse gases through a "biological pump": Marine vegetation absorbs CO2 through photosynthesis, and when these organisms die, they (and the CO2) end up at the bottom of the ocean, away from the atmosphere.

Forty percent of human-emitted CO2 in the last 200 years has been absorbed by the oceans (through both a biological and physical pump. A physical pump is a natural cycle: cooler and heavier ocean water, which has locked in carbon, sinks to the ocean floor and can stay for centuries. Eventually, these cold currents rise up towards the surface again and are warmed. This warm water releases its stored carbon as CO2)*.

So what’s the problem?

An increase of CO2 in the ocean causes an increase in acidity of the ocean (this has gone up by 30% since the Industrial Revolution more than 200 years ago). This is often referred to as “global warming’s evil twin” or “the other carbon problem”.

Why? Because ocean acidification impacts marine organisms, including the famous corals reefs and less glamorous phytoplankton. The death of these marine organisms (which, you remember, are responsible for storing greenhouse gases) means a reduction in the absorption of CO2. Instead, it stays in the atmosphere.

Not only does ocean acidification adversely impact marine ecosystems, it also has major consequences for the global economy. For example, in 2007, oyster larvae in hatcheries on the US west coast began dying at an unprecedented rate due to local changes in ocean acidity. This pushed this industry to the brink of collapse.

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And it doesn’t end there. Coming back to the rise in sea levels, the melting of fresh water glaciers also changes the salinity levels of oceans and seas. Rising temperatures lead to warmer ocean waters, which absorb less CO2 than cooler oceans (see the explanation on 'physical pump').

The rapid warming of the Arctic Ocean is leading to releases of methane trapped in the permafrost. Warming of tropical seas is leading to bleaching and die offs of coral reefs, which in turn hits both biodiversity and carbon capturing capacity.

Can oceans save the planet?

The role of oceans as climate regulators is fundamental for the survival of the planet. Climate change does occur naturally, and marine ecosystems – like terrestrial ones – have adapted over time to these changes, but oceans were, are and will not be ready for the rapid climate change caused by man-made factors.

The rate of change of ocean acidification is nearly 10 times faster than at any time in the last 65 million years. So while ocean chemistry is a natural buffer mechanism for carbon emissions, it cannot keep up with the current rate of change, and marine organisms are struggling to adapt.

At this pace, we cannot continue to rely on natural processes and ecosystems to bail us out. The transition to a low carbon economy is urgent for the survival of ocean life, and for the climate regulation that makes the Earth livable. 


*This article has been corrected to reflect that the 40% of the absorption of anthropogenic CO2 in the last 200 years has been through biological and physical pump.

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