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Andreas Wilson-Späth
With many of us wilting in this summer’s heat wave and with 2015 having been declared the hottest year on record, we may be excused for thinking that climate change is having its biggest impact on land. But increasingly, scientists are discovering that the effects human activities are equally severe on the world’s oceans and that the consequences are potentially devastating, even for us landlubbers.
How is climate-changing humanity affecting the seas? Here are just a few of the more recent lowlights:
The heat is on
A study published in January suggests that the last 20 years have seen half of the increase in the oceans’ heat content that has accumulated since the pre-industrial era.
Seawater has absorbed over 90% of the excess heat produced as a result of the burning of fossil fuels. “The findings are concerning,” lead author Peter Gleckler told The Guardian. “It’s clear evidence that the oceans are taking the brunt of the greenhouse gases and are accumulating a lot of heat”.
Surf’s up
As seawater heats up due to global warming, it expands. This is a well-known process, of course, but new research shows that its effects have been underestimated until now. It turns out that in terms of rising sea level, its contribution is almost twice as much as scientists had assumed it was – around 1.4mm per year instead of only 0.7 to 1.0mm (when melting ice is taken into account as well, sea level is rising at about 2.74mm annually).
Sounds like a small and slow change, but over time, it means that the chances of storm surges, which can be very destructive in coastal regions, may increase substantially.
Acid reflux and tipsy fish
Carbon dioxide dissolves in seawater. As humans burn fossil fuels, puffing more and more carbon dioxide into the air, more and more of it ends up in the oceans.
A new paper indicates that in the last ten years, the North Atlantic has soaked up 50% more carbon dioxide from burnt oil, coal and natural gas than it did during the previous decade.
While this process has helped to buffer some of the greenhouse effect caused by carbon dioxide in the atmosphere, it is also making seawater more and more acidic, lowering its pH with detrimental effects on a variety of ocean-dwelling creatures, including molluscs and coral.
In addition, the rising carbon dioxide content of seawater is threatening to influence fish populations many years earlier than previously forecast. So say Australian researchers in a study published in the journal Nature in January.
Ben McNeil, one of the authors explains that "high concentrations of carbon dioxide cause fish to become intoxicated – a phenomenon known as hypercapnia. Essentially, the fish become lost at sea. The carbon dioxide affects their brains and they lose their sense of direction and ability to find their way home. They don't even know where their predators are”.
If things continue at the current rate, McNeil says episodes of hypercapnia can be expected to occur in certain parts of the oceans by the middle of the century, decades earlier than predicted until now.
Less krill
The planet’s stock of krill – tiny, widespread and multitudinous crustaceans which float in seawater and form the basis of much of the marine food chain – is also increasingly in peril as carbon dioxide levels rise.
Ocean acidification makes the reproductive cycle of krill – from the hatching of eggs to the development of larva – more precarious. According to Dr So Kawaguchi of the Australian government’s Antarctic Division, “if we continue with business as usual, and we don’t act on reducing carbon emissions [...], there could be a 20 to 70% reduction in Antarctic krill by 2100” and that can’t be good.
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