Andreas Späth

Our warming oceans

2014-02-17 12:15

Andreas Wilson-Späth

The earth’s oceans are intimately connected to its climate. They absorb and store huge quantities of CO2, buffering its global warming potential. They also serve as a gigantic heat sink that removes energy from the atmosphere, moderates global surface temperatures and significantly affects weather patterns.

But there is only so much we can expect the oceans to accomplish as we keep on spewing greenhouse gasses into the air. As voluminous as they are, the world’s seas are a finite reservoir that will not continue to soak up our fossil fuel sins forever.

Recently there has been a lot of talk about a pause in global warming. While the planet as a whole has continued to get hotter, records show a more gradual increase in global surface temperatures during the last decade or so compared to the more rapid warming of the 1980s and 1990s.

Studies show that most of the surplus heat has ended up in the oceans, explaining the hiatus in surface temperatures.

Impacts on marine ecosystems

It’s well established that about 90% of the energy of global warming is absorbed by seawater and in recent years, ocean warming has escalated. One observer points out that in 2013, when the energy content of the top 700 metres of water in the oceans reached higher levels than ever recorded before, the oceans collectively absorbed an amount of thermal energy equivalent to more than 12 Hiroshima bombs every second.

As seawater heats up, it expands, adding to sea level rise, while its increased energy content helps to fuel storms. Rising water temperatures are also having substantial impacts on marine ecosystems, affecting plankton production, driving some fish species to cooler and deeper regions and leading to a reduction in size in others, all of which puts growing pressure on the fishing industry worldwide.

Last year, a group of scientists confirmed that the apparent hiatus in global warming could be explained as a result of increased heat uptake in the Pacific and Atlantic.

This month, a new study published in the journal Nature Climate Change offers a mechanism for the process: unusually powerful trade winds in the eastern and central Pacific have effectively ploughed heat, in the form of warm surface water, into deeper parts of the ocean, resulting in a net cooling effect on average global surface temperatures estimated at 0.1 to 0.2oC.

No time for complacency

While the causes of the accelerated winds remain unexplained, the paper suggests that the hiatus could “persist for much of the present decade if the trade wind trends continue, however rapid warming is expected to resume once the anomalous wind trends abate”.

The research grants us no time for complacency. In the words of lead author Matthew England from Sidney’s University of New South Wales, “even if the winds accelerate even further, sooner or later the impact of greenhouse gases will overwhelm the effect. And if the winds relax, the heat will come out quickly”.

Knowingly or not, we’ve been using the world’s oceans as a sponge to mop up our global warming mess for too long. When their finite capacity to do so is exceeded, it’ll be payback time.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
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