Drawing lines on a map won’t protect marine ecosystems from the impacts of climate change, and neither will decades of conservation in the marine protected areas (MPAs) between those lines, according to new research.

As the ocean as a whole warms, so too will waters within the world’s MPAs, and that heat will surpass what the species living in them can tolerate, scientists found. If greenhouse gas emissions continue at their current rate, by mid-century the maximum temperatures in nearly half of existing MPAs – mostly in the tropics – will surpass their inhabitants’ tolerance. On average, surface temperatures in marine reserves will rise 2.8C (5F) by 2100.

“What we found is that that the degree of warming is most likely to exceed the ability of most animals to survive there,” said John Bruno, a marine biologist at the University of North Carolina and lead author of the new study that was published Monday in the journal Nature Climate Change.

The findings paint a bleak picture of the future of marine biodiversity, showing that even large MPAs that impose bans on fishing and other extractive activities won’t blunt the effects of climate change – deoxygenation, acidification and coral bleaching. While marine refuges may still have value in the short term, the study suggests there are few viable solutions for protecting their biodiversity over the long run, short of slashing greenhouse gas emissions.

“We were just surprised by the numbers,” Bruno said. “We’re seeing fish dying and coral disappearing due to, like, 0.7 degrees of warming. Assume 3 degrees would just be a wipeout.”

In recent years, there has been a dramatic increase in the number and size of MPAs as governments work toward a United Nations goal of protecting 10 percent of the ocean in reserves by 2020.

To assess the long-term benefits of those reserves, Bruno and colleagues modeled changes in sea surface temperatures and oxygen concentrations in the geographic centers of 8,236 MPAs, 309 of which ban fishing.

They found that under a “business as usual” scenario, average temperatures would increase by at least 2C (3.6F) in 99 percent of the MPAs by 2100. In a lower-emissions case in which emissions peak around 2040 and the atmosphere’s carbon dioxide concentration stabilizes around 525 parts per million by the end of the century, waters would warm about half as quickly.

The fastest increases would occur in polar regions – with temperatures rising by more than 0.1 percent a year in some places – though tropical regions would suffer severe biodiversity losses as species there move into cooler waters.

Some of the impacts are already being seen in protected habitats. Australia’s Great Barrier Reef Marine Park is the world’s biggest coral ecosystem and includes 600 coral species. In March 2016, coral bleaching triggered by record high ocean temperatures killed a third of the Great Barrier Reef’s corals. “Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, suggesting that local protection of reefs affords little or no resistance to extreme heat,” scientists wrote in a study published last year.

The researchers also found that surviving past bleaching events hadn’t increased corals’ resiliency to high temperatures and that “immediate global action to curb future warming is essential to secure a future for coral reefs.”

“Spikes in temperatures are more important and more deadly than slow rises in average temperatures,” said Terry Hughes, the lead author of the Great Barrier study and director of the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University in Townsville, Australia.

Hughes noted that gradual rises in sea temperatures will also “test the physiology of marine species, regardless of whether they are protected from fishing inside MPAs.”

“MPAs provide no protection from hot water – although the slow recovery afterwards may be faster inside an MPA compared to adjoining areas with little or no local protection,” he added.

Bruno’s research suggests that last point may not be universally true. He said that it’s “widely believed that if fishing pressure and pollution are mitigated, then we would see more resiliency.” But they saw “no buffering impact” from MPAs in the study.

“Nothing short of radically reducing carbon emissions can make much of a difference,” Bruno said.

Without those radical reductions, is there still a point to establishing and maintaining MPAs?

Bruno and others say yes, but that over time it might be better to focus on places that are more likely to survive as temperatures continue to rise.

“I’m not saying we should get rid of them,” Bruno said, adding that factors like overfishing also have huge effects on marine life that are easier to combat. For instance, he said it could make sense to protect ecosystems off the west coast of the United States where temperatures will remain cool enough to still allow some amount of biodiversity to flourish. “There will be different fauna – from Baja,” Bruno noted. “But it’s worth protecting even though there will be different stuff there.”

Lance Morgan, president of the Marine Conservation Institute, said when questions like these come up, he’s always reminded of a “Far Side” cartoon in which two men fishing from a boat watch atomic mushroom clouds on the horizon. One says, “I’ll tell you what this means, Norm – no size restrictions and screw the limit.”

“It’s worth retaining hope even when the predictions require us to be very cynical and pessimistic,” said Morgan, whose organization advocates for marine protected areas. “Everything isn’t going to die with climate change.”

He said some organisms will be strong enough to survive as the climate warms, and it’s worth protecting a future for whatever we can. “If we say all bets are off and do whatever the hell we want, then for sure [there] won’t be anything there,” Morgan said.

More connectivity between MPAs as species migrate to stay in their temperature-tolerance zones might help, he added. His group and others have recommended protecting 30 percent of the ocean in reserves.

The new study reinforces the need for such action, said Angelo Villagomez, a senior officer at the Pew Bertarelli Ocean Legacy project, which works to establish MPAs. “The best thing we could do is to protect 30 percent of every ocean habitat, as those areas will be the refuges for many species facing a warming planet.”