Global warming is set to wipe out “many if not most” of the animals living in protected parts of the world’s oceans by the end of the century, scientists predict.
Polar bears and penguins are among the species under greatest threat, even if carbon emission trends remain unchanged.
Current “business-as-usual” projections suggest that by 2100 Marine Protected Areas (MPAs) will be 2.8C warmer than they are today.
That is enough to make the conservation zones uninhabitable for many of the fish, mammals, birds and invertebrates now dwelling within them, say the researchers.
There are 8,236 MPAs around the world, covering 4% of the total surface of the oceans.
They were set up to provide safe havens for wildlife and conserve endangered habitats by restricting human activities such as fishing, mining and tourism.
The new study published in the journal Nature Climate Change suggests that without drastic action MPAs will be “devastated” by rapid global warming.
Lead scientist Professor John Bruno, from the University of North Carolina in the US, said: “With warming of this magnitude, we expect to lose many, if not most, animal species from Marine Protected Areas by the turn of the century.
“To avoid the worst outcomes, we need to immediately adopt an emission reduction scenario in which emissions peak within the next two decades and then decrease very significantly, replacing fossil fuels with cleaner energy sources like solar and wind.”
The scientists carried out simulations to model sea surface temperatures and oxygen concentrations in MPAs around the world, including those where fishing is banned.
They found that even under the Intergovernmental Panel on Climate Change (IPCC) “business-as-usual” emissions scenario, MPAs were expected to warm by 0.034C per year.
By the end of the century ocean temperatures in MPAs will have increased by an average of 2.8C, they said.
For each MPA the scientists calculated a “community thermal safety margin” (CTSM), the critical point after which most species would not be able to tolerate further change in their living conditions.
In tropical areas, this threshold was expected to be reached by about 2050.
MPAs in the Arctic and Antarctic were among those at greatest risk, said the scientists. They were likely to warm especially quickly, further endangering already vulnerable polar bears and penguins.
Other high-risk MPAs included those off the northern Galapagos islands Darwin and Wolf.
Co-author Rich Aronson, an ocean scientist at the Florida Institute of Technology, said: “There has been a lot of talk about establishing marine reserves to buy time while we figure out how to confront climate change.
“We’re out of time, and the fact is we already know what to do. We have to control greenhouse gas emissions.”