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Is This Fish Winning Climate Change?

This summer, we asked readers to send us their climate change questions. And they did. We received many, many, many climate change questions. So many, in fact, that we’re doing several different projects around them. The main column, Climate Questions from an Adult, explores the business, culture and chemistry behind your pressing climate queries. Today, in another edition of our second column, Who’s Winning Climate Change, we’re diving into the strange stories and complex choices that arise when a warmer planet isn’t 100 percent terrible for everyone.

“There are many articles about how climate change has been detrimental to animal habitat, but I wonder, are there any animals that will benefit from climate change that pose no risk to humans, so not mosquitoes, ticks or any other disease vector?” — Roberto Romero, California.

Picture a tropical fish — a shimmery pancake of an animal with an Instagram pucker and a penchant for nibbling the algae off tropical coral. In the warm waters of northeastern Australia, fish just like this, called sawtails, have long lived as part of the ecosystem of the Great Barrier Reef. Unfortunately for them, the reef is dying, bleaching like a cattle skull in the sun as climate change makes the surrounding water a little too warm.

Now picture a kelp forest — seaweed redwoods lazily undulating in the cool ocean current of southeast Australia. Another victim of climate change, the kelp are struggling to survive the voracious sawtails that have swum in on newly warmer currents. The fish nibble, and they nibble, until there’s nothing left of the kelp to grow back. In their wake, corals cling to the freshly exposed rocks. New reefs begin to grow.

“I guess my point is that it’s difficult to say what is a winner and what is a loser,” said Brett Scheffers, a professor of wildlife ecology and conservation at the University of Florida. The sawtail is a loser in its native habitat — and a winner in the one it’s slowly colonizing someplace else. And it’s not alone. All over the world, animals and plants are being forced to respond to a changing climate. Some of those species will clearly and decisively lose. But many others, like the sawtail, have tourney stats that are a little harder to parse. Whether they’re winning depends on when you assess them and where they are — and it depends on how humans respond to them.

From polar bears to sea turtles, loser species often get all the attention, said Stephen Hamilton, professor of ecology at Michigan State. Meanwhile, the species that look like winners also often look like a lot of bad news: Think about tropical dengue-carrying mosquitoes or tree-killing gypsy moths slouching northward.

But there really are some animals and plants that are surviving and thriving, or are projected to, as the world warms. And they aren’t all invasive species or creatures that seem to malignly have it in for the human race, said Cascade Sorte, a professor of ecology at the University of California, Irvine. Instead, she told me, the species that seem destined for success tend to fall into one of two categories: Things that can take a pounding and get back up like they’re trying to steal the title from Apollo Creed — and things that can reproduce really, really fast.

Those skills are important because climate change isn’t a single shift from one condition to another. “There’s no equilibrium,” Hamilton said. No “new normal” that we will reach and stabilize at. Instead, you’re talking about ongoing change.

To do well under those conditions, a species has to be extremely flexible. There are a couple key traits that help. Sorte used two species that were surviving happily in the warming waters of the Gulf of Maine as her examples. If a species is hardy, it can handle living on the edges of its comfortable habitat, like the barnacles that live high on coastal rocks and can survive being exposed to the air and blazing sun for long periods. If it reproduces fast, it can move into a new environment and establish itself more easily, like thin-bladed sea lettuce that can throw down roots, grow quickly and spread.

Granted, many of the classic invasive species fit this description, since they’ve had to adapt to a new climate somewhere along the way. But that doesn’t mean all species that are winning climate change are necessarily invasive — at least not in the same sense as something like kudzu or the emerald ash borer, both species that were brought by humans (whether intentionally or accidentally) to a new environment where they proceeded to take over. In fact, some studies show that climate change-related droughts in the southwest United States could actually favor native species, Sorte said, because those species were already well adapted to surviving on little water. True invasives aren’t.

Instead, Scheffers said, a lot of the species that are winning climate change are doing so as part of what he calls “mass redistribution” — animals and plants that move, on their own accord, as their own native environment also moves. Consider the lobster. Over the course of about 20 years, the lobster harvest in southern New England and New York all but collapsed — with the catch falling by 97 percent from 1996 to 2014. Meanwhile, in Maine, where the water is still a comfortable lobster temperature, the catch rose by 219 percent in roughly the same time period.

The water got warmer, and the lobsters moved.

Whether that counts as winning is complex, though. The lobster species is doing fine. So from their perspective: solid win. Same for the Maine fishermen who ended up with a lobster boom. But the Gulf of Maine Lobster Paradise is not a constant that will now stick around forever. Already, ideal temperatures (and lobsters) are moving to Canadian waters. Any fishing industry left behind by the lobsters’ scrappy march toward survival is unlikely to feel particularly blessed. And, Scheffers said, we know very little about interactions between species as these migrations happen. Are there any species being displaced by lobsters in the same way Australian sawtails are devouring kelp forests? Hard to say.

What’s more, as species migrate and redistribute themselves as a means of adaptation, they might run headlong into humans’ difficulty adjusting to change. Scheffers talked about the plight of the brown cowbird, a species native to North America that moved eastward across the continent in response to forest clearing and other human-induced environmental changes. A lot of people think of them as invasive, he said, and treat them as such — including intentionally culling the birds to protect native species.

Now imagine what might happen as plants and animals native to Mexico start to follow the temperatures they’re adapted to northward. What happens if they displace or outcompete the plants and animals that were already here? “Will we call them invasive?” Scheffers asked. A species could adapt to climate change only to end up being harmed by the people in their new environment. “If we suddenly treat them like cowbirds, they have no protection and we cull them, it creates a lot of complications,” Scheffers said.

That’s just one of the things that makes determining climate winners and losers tough all around. Win/lose, good/bad — those aren’t science things. Those are value judgements humans make individually, and subjectively, Sorte said. After all, the concept of an ambiguous climate win isn’t limited to fish on the Great Barrier Reef. “Imagine it snows less,” Sorte said. “That’s bad if you love to ski. But it’s good if you don’t like shoveling the drive.” Same with the animals.

Maggie Koerth is a senior science writer for FiveThirtyEight.

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