Climate change and the seas

Climate change and the seas


Climate change is warming the oceans, causing acidification of marine environments, and changing rainfall patterns. This combination of factors often exacerbates the impacts of other human pressures on the seas, leading to loss of marine biodiversity. Many human livelihoods depend on marine biodiversity and ecosystems, so action to limit ocean warming must be taken quickly.

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The oceans absorb heat from the atmosphere. Measurements now show that the warming of the oceans has affected areas far below the ocean surface in recent decades. The effect on marine life of warming oceans is strong, and biodiversity is at ever greater risk. Nowhere is this more clearly highlighted than in the case of warmer-water plankton in the Northeast Atlantic. Some copepod are moving northwards at a rate of 200-250 km per decade. These small copepods are near the bottom of the food chain. Fish and other animals of the Northeast Atlantic feed on these copepods and their distribution pattern in the oceans may change as a result of the copepods’ northward movement.

Animals living outside their optimal temperature range expend more energy on respiration to the detriment of their other functions. This weakens them, making them more vulnerable to disease, and allowing other species that are better suited to the new temperature regime to get a competitive advantage. In addition, the spores, eggs, or offspring of these animals will struggle to develop in suboptimal temperatures. As some species suffer in the new conditions, this can have spillover effects on the other organisms that depend on or interact with them. This chain of events ultimately influences the overall functioning of the ecosystem, which can lead to loss of biodiversity. This is exactly what is happening with copepods: because they are eaten by so many other organisms their suffering influences the entire food web.

Higher up in the food chain, animals that cannot find food are forced to move in order to survive. In Europe, where sea surface temperature is increasing more rapidly than in the global oceans, they move predominantly northwards. This phenomenon can affect fish stocks, as illustrated by the way mackerel have started to spend more time in more northern waters. This can have a knock-on effect on local fishermen and communities further afield. One of the knock-on effects was the infamous ‘mackerel war’ between the EU and the Faroe Islands. The ‘mackerel war’ arose partly because of overfishing of blue whiting and partly as a direct result of fish species, including herring and mackerel, moving further north in response to rising sea temperatures. The extra time spent by the fish stocks in Faroese waters resulted in a disagreement on fishing rights. From a Faroese perspective, they had a right to the fish in their waters, but from an EU perspective, agreements on sustainable fishing quotas were being breached, potentially leading to the risk of overfishing with the loss of EU income and jobs as a consequence. The dispute came to an end in 2014, when the EU lifted import bans on the fish caught in Faroese waters in return for an end to fishing carried out by the islanders.

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