Marine problems: climate change | WWF

The marine environment is already registering the impacts of climate change. The current increase in global temperature of 0.7°C since pre-industrial times is disrupting life in the oceans, from the tropics to the poles.

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Marine species affected by climate change include plankton - which forms the basis of marine food chains - corals, fish, polar bears, walruses, seals, sea lions, penguins, and seabirds.

The Intergovernmental Panel on Climate Change predicts a further rise of between 1.4°C and 5.8°C by the end of the century. Climate change could therefore well be the knock-out punch for many species which are already under stress from overfishing and habitat loss.

The key impacts of climate change on the marine environment are...

Coral bleaching

One of the most visually dramatic effects of climate change is coral bleaching, a stress response caused by high water temperatures that can lead to coral death. 

Recent years have seen widespread and severe coral bleaching episodes around the world, with coral mortality reaching 70% in some regions.

More on coral bleaching

Stormy weather 

Most scientists believe that global warming will herald a new era of extreme and unpredictable weather.

Tropical storms and heavier rainfall may increase and so too would the consequent physical damage to coral reefs, other coastal ecosystems, and coastal communities. Hurricanes Hugo and Marilyn hit the US Virgin Islands National Park in 1989 and 1995, respectively, and did massive damage to coral ecosystems.

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Moving homes? 

As the oceans warm, the location of the ideal water temperature may shift for many species. 

A study has shown that fish in the North Sea have moved further north or into deeper water in response to rising sea temperatures. Other species may lose their homes for other reasons. The distribution of penguin species in the Antarctic Peninsula region, for example, is changing with reductions in sea ice due to global warming.

More on the impact of climate change on species

© WWF / Tom Arnbom
A walrus on the ice on Svalbard
© WWF / Tom Arnbom

Changes to marine ecosystems from rising global temperatures will have an impact on walrus and other marine mammals.

Coral bleaching due to temperature rise, Indo-Pacific Ocean. 
© WWF / Jürgen FREUND
Coral bleaching due to temperature rise, Indo-Pacific Ocean.
© WWF / Jürgen FREUND

Altered lifestyles 

Rising temperatures can directly affect the metabolism, life cycle, and behaviour of marine species. 

For many species, temperature serves as a cue for reproduction. Clearly, changes in sea temperature could affect their successful breeding.

The number of male and female offspring is determined by temperature for marine turtles, as well as some fish and copepods (tiny shrimp-like animals on which many other marine animals feed). Changing climate could therefore skew sex ratios and threaten population survival.

Hawksbill turtle (<i>Eretmochelys imbricata</i>). The metabolism, life cycle, and ... 
© WWF / Martin HARVEY
Hawksbill turtle (Eretmochelys imbricata). The metabolism, life cycle, and behaviour of many marine species could be affected by climate change.
© WWF / Martin HARVEY

Rising sea levels

Global sea levels may rise by as much as 69cm during the next 100 years due to melting of glaciers and polar ice, and thermal expansion of warmer water. 

Rising water levels will have serious impacts on marine ecosystems. The amount of light reaching offshore plants and algae dependent on photosynthesis could be reduced, while coastal habitats are already being flooded.

Rapid sea level rise will likely be the greatest climate change challenge to mangrove ecosystems, which require stable sea levels for long-term survival.

More on rising sea levels


Decreased Mixing

Vertical mixing in the ocean is important for many reasons, including transporting nutrients from deep to shallow waters, and surface water rich in oxygen into deeper waters. In some areas, changes to ocean temperature profiles induced by climate change are causing a reduction in the amount of mixing, and for example, reducing oxygen levels at depth.

Acidic oceans

After absorbing a large proportion of the carbon dioxide released by human activities, the oceans are becoming acidic. If it weren’t for the oceans, the level of carbon dioxide in the atmosphere would be much higher.

The effect could be that fish, squid, and other gilled marine animals may find it harder to "breathe", as the dissolved oxygen essential for their life becomes difficult to extract as water becomes more acidic. And shellfish, crabs, lobsters, and corals may find it more difficult to build their calcium carbonate shells. In some areas, calcium carbonate shells may even start to dissolve.

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