Under Fire

Like many scientists who began their research careers in the 1990s, biologist and author Thor Hanson has watched climate change grow from a background concern to a forefront issue. Humanity, he says, is late to the game, because “while people may have spent the past thirty years struggling to even think about a response, every other species on the planet has simply been getting on with it.”

Plant and animal species have undergone enormous changes in the twenty-first century, including mass migrations, unusual adaptations, and cascading extinctions on a scale not seen since the end of the last ice age — around ten thousand years ago. In his latest book, Hurricane Lizards and Plastic Squid: The Fraught and Fascinating Biology of Climate Change, Hanson offers dozens of examples of these changes, many of which have profound implications for how humanity can live on a planet that’s transforming before our eyes.

As a child raised in the Pacific Northwest, Hanson caught his first salmon at the age of four and kept snakes, caterpillars, frogs, and crabs as “summertime pets.” Today he travels the world — from the desert of California’s Joshua Tree National Park to Tanzania’s Usambara Mountains — but still comes home to Washington State, where he lives on San Juan Island with his wife, who’s a botanist, and their teenage son.

Trained as both a biologist and a botanist, Hanson earned his bachelor’s degree from the University of Redlands, his master’s from the University of Vermont’s Field Naturalist Program, and a doctorate through a joint program of the University of Idaho and the Tropical Agricultural Research and Higher Education Center in Costa Rica. As an independent conservation biologist, he has studied wild bees, songbirds, rainforests, marine ecosystems, and a number of endangered species. He’s also written about the relationship between armed conflict and biodiversity. He’s been a Guggenheim and Switzer Environmental Fellow, cohosted the PBS Nature series American Spring LIVE, and has often appeared on such NPR programs as Fresh Air, Science Friday, and The World.

For this interview I talked to Hanson over video chat: I was in my cabin at 3,200 feet in the Sierra foothills of Northern California, and he was on a hilltop near his isolated island home, where he could get decent cell-phone reception. With his computer by his side, he enjoyed a light wind blowing through the acres of grass surrounding him.

Leviton: Biodiversity comes from specialization, with millions of species finding ways to adapt to their specific environment. Have the environmental changes caused by human activity over the last three hundred years been a particularly difficult problem for wild animals?

Hanson: It’s important to remember that change is inherent, and evolution is all about change. What’s different now is the pace of change. Over the course of geologic time there have been other eras where the climate has transformed rapidly, and those have always been accompanied by a huge loss of biodiversity and mass-extinction events — the same sort of trends we see happening now.

Climate change is occurring on top of many other human-related stressors that have been affecting plants and animals, particularly since the Industrial Revolution began in the mid-eighteenth century. Industrialization had a huge impact on the environment: habitat loss, pollution, overhunting, and overharvesting of resources. And now we’ve added a warming world to accelerate and amplify those other threats. So this really is an inflection point for plants and animals on our planet.

Leviton: In your latest book you write that “extinction is the fate of all species.” That’s grim.

Hanson: Yes, it is. In the history of life on the planet, species have come and gone. Some branches of the evolutionary tree are chopped off quickly, while others persist longer. But ultimately the end comes for every species that has been or ever will be.

One of the questions I often get is: How long will we last? Humans aren’t very old, as species go. Depending on where you draw the line, Homo sapiens might be 250,000 to 300,000 years old. That’s an eyeblink in evolutionary time. And we are at the end of a branch. Our genus has just one species: us. All the other species in the genus Homo have disappeared. We are very prolific and successful in terms of numbers, thanks to our big brains, but biologically we’re sort of at a dead end: the last survivor of a genus that was never very diverse to begin with. Compared to many other creatures out there, which have huge diversity within their genera and have been around for millions of years, we are newcomers.

Leviton: Many people treat the extinction of a plant or animal species as an absolute disaster, but is it really so important that, for instance, the Chinese paddlefish and the mountain mist frog were officially declared extinct in 2022?

Hanson: There’s always a sort of background extinction going on in nature, but by most estimates the current rate of extinction is thousands of times higher than normal. That is a cause for great concern. It can destabilize ecosystems. You start pulling out too many pieces, and the whole system becomes fragile. If you lose what’s called a “keystone species” — one on which other species in the ecosystem depend — the effect is huge.

Leviton: Worldwide we are losing insects of all kinds at an unprecedented rate of 2 percent per year. Nobody complains about the lack of mosquitoes or midges, but they are important, aren’t they?

Hanson: Correct. There are a lot of creatures out there, particularly the arthropods — those with exoskeletons — that we aren’t very fond of. Nonetheless they are totally essential. They form the basis of food webs everywhere and are one of the major links between plants, which fix energy from the sun, and the rest of nature. Maybe you don’t like moths and flies when they get into your house, but without them you won’t have any birds. A mated pair of chickadees, for example, will capture between six and nine thousand moth caterpillars to feed to their nestlings. And that’s within an area the size of an average backyard. Your yard needs to be full of insects if you’re going to have the rest of the food web.

Leviton: Scientists looking at the effects of climate change on animals and plants talk about “punctuated equilibrium.” What is that, and how does it help explain evolutionary theory?

Hanson: Our classic idea of evolution comes from Charles Darwin, who pictured it as this slow, incremental process of change governed by natural selection, or the “survival of the fittest.” Species change to adapt to shifts in their environment and even become new species, but slowly. Yet when we look at the fossil record, we see these great leaps occur, like the sudden appearance of flowering plants. In all these layers of rock, there are no fossils of flowering plants, and then suddenly: boom! There are flowering plants everywhere, and they are diverse. Darwin was very aware of the fossil record and concerned about what it showed. It didn’t always look like a slow process.

In 1972 paleontologists Niles Eldredge and Stephen Jay Gould coined the term “punctuated equilibrium” to explain the periods of rapid change after much longer periods of calm. If you look at trilobites, for example, which are marine arthropods, they stayed pretty much the same for a very long time, and then there was a sudden change in diversity. There are still arguments about what’s going on there. A lot of people think that rapid environmental change, the kind that has severe consequences for organisms, leads to periods of rapid evolutionary change. Just as a stable environment tends to encourage stability in organisms, if the environment is getting hotter — or wetter, or drier — over a short period of time, that’s going to lead to dramatic change.

Leviton: You write about how rapidly creatures can adapt to changes in the environment. They don’t always need a thousand, or even a hundred, years to make big adjustments.

Hanson: Yes, evolution is not always this slow process that we can’t really see happening. We’ve got changes playing out now with astounding rapidity. Biologists can see natural selection occurring over the course of a field season — the short period of time they get to spend outside monitoring wildlife. It’s truly remarkable the way some organisms are adapting to climate change. Of course, their ability to adapt does nothing to alleviate our concerns about the crisis. If anything, the widespread changes we are seeing make us more concerned. But studying these adaptations can help us identify the issues that are most important and the species that need the most help. This may not make us worry less, but it can help us worry smarter.

Leviton: Up here in the Sierras, where I live, the last ten years have brought not only longer summers — which we call fire season — but also longer winters. We’ve had two winters in a row that were dubbed Snowmageddon 1 and 2. Record-breaking amounts of precipitation fell on elevations that rarely see any. Spring and autumn seem to have contracted. Are other areas seeing a similar shift in the seasons?

Hanson: We are seeing rapid changes in seasonal processes, especially near the poles and in temperate areas, like where you and I live. We see flowers blooming at different times than they did even thirty years ago. And when that happens, it can destabilize ecosystems.

Many plants and animals respond to seasonal changes in temperature, but there are others that respond to changes in day length. We may be warming this planet, but we’re not altering its orbit around the sun or the tilt of its axis. So if you’re a migratory bird using day length to tell you when to begin your migration, you’re on one clock. Because of climate change, you might arrive at a critical stopping point of your journey — where for countless generations your species has refueled on some insect population that’s usually common at that time — and find that those insects have responded to a temperature change: their peak abundance was weeks ago, and you’ve missed the boat, because they were on a different clock.

Leviton: Individual trees may not move — they’re rooted in the ground — but forests do. How do forests change their location in reaction to changes in the environment?

Hanson: Trees seem stable — so stable we have legends about their stability, like Yggdrasil, the sacred world tree in Norse cosmology. But stability is just one phase of their life cycle. Trees and other plants have a mobile part of their life cycle, too: when they’re seeds. Whether blown by a wind, or trapped inside a fruit that might be devoured by another creature, or stuck to your pant leg, seeds sometimes travel long distances. Blue jays, to name one example, can carry acorns over two miles, helping spread oak trees.

The way to study the movement of forests is to look at where those seeds germinate and grow into saplings. The U.S. Forest Service has been gathering huge quantities of data on this for decades. Every year they report exactly what’s growing where. It’s so much data it will crash a spreadsheet on a typical laptop. But if you have a really powerful computer, you can see the trends. You can pinpoint the exact place in the landscape where you would be most likely to bump into, say, a red oak as you wandered through the forest. That’s the center of that species’ range, where the conditions for the red oak are the best. And in other parts of that range the old red oaks are dying, and the seeds aren’t germinating well. Maybe it’s becoming too hot or too dry. When you’re in the woods and look up at the trees, you are looking at the past. The old trees represent the environmental conditions decades ago, when they sprouted and grew to adulthood. If you want to look at the future, look down at the seedlings and saplings in that environment. Then you see what the forest will look like in the coming years.

What the Forest Service data shows is that the centers of most trees’ ranges are moving, because the places where they have the most success are changing. One study found that tree species in eastern North American forests are moving at an average rate of fifteen kilometers westward and eleven kilometers northward every decade. In some cases the trees are moving their ranges faster than birds are.

Evolution is not always this slow process that we can’t really see happening. We’ve got changes playing out now with astounding rapidity. Biologists can see natural selection occurring over the course of a field season.

Leviton: There’s also been a big range shift for pelicans, which you observed when you were working on a whale-research project in the Northwest.

Hanson: The current shift in ranges for all wildlife is the biggest biological reorganization since the end of the last ice age, maybe longer. Estimates are that somewhere between 25 and 85 percent of all species are shifting their ranges in response to climate change. Even at the low end, that’s one out of four species on the planet! Some are moving short distances, while others are moving as far as it takes.

The brown pelican used to breed only off the coast of Southern California or Mexico, moving north on a seasonal basis to feed, never going farther than southern Oregon. Now they can live year-round here in Washington State. We’re seeing breeding behavior at the mouth of the Columbia River, where they’ve been gathering on islands in huge numbers. Biologists have counted sixteen thousand pelicans in an area where they used to count no more than a hundred. They’ve been seen in British Columbia and even the panhandle of Alaska.

We can see similar changes in backyard bird populations. Hummingbirds are expanding northward. The Anna’s hummingbird that used to live only in Baja and Southern California is now resident in your area in the Sierras and in the state of Washington. It’s moving up into British Columbia.

Leviton: And it’s not just across the surface of the earth where we see movement of species. They also move to higher or lower altitudes.

Hanson: Yes, as you go farther and farther from the equator, temperatures get colder. We all know this. But the same thing happens as you ascend a mountainside: the higher you go, the lower the temperature. So if you live on a flat landscape, maybe you move north when temperatures warm. But if there’s a mountain right next to you, you can go up and find cooler conditions. This is all well and good for species that start at the bottom of the mountain, because they can find nicer temperatures right up the hill. But it’s a big problem for the species that were already at the top. Where do they go? They have no higher elevation to retreat to, and their populations can wink out. Biologists call this the “escalator to extinction.” On tropical mountaintops the local populations are often depleted or gone. There could be even higher mountains where those species still exist, but they are becoming extinct in areas where they used to thrive, which makes global extinction more likely.

Warming is causing major disruptions and stress on marine ecosystems, from widespread coral bleaching to the mass redistribution of species into new areas.

Leviton: Let’s talk about ocean temperatures and levels. What effects are they having on wildlife?

Hanson: The ocean temperature, going down to two thousand feet or so below the surface, has risen about 1.5 degrees Fahrenheit since 1900, and much of that increase has occurred in the last thirty years. The change is the fastest at the poles, but warm currents and marine heat waves are bringing rapid change to locations all over the world. In some places along coastlines, upwellings of deeper, colder water create little refuges where you can see glimpses of the old ecosystem. But overall, warming is causing major disruptions and stress on marine ecosystems, from widespread coral bleaching to the mass redistribution of species into new areas.

Species that can adapt to the new conditions often do so because of “plasticity” — the inherent ability of an organism to respond to changes in its environment. If a species already has enough flexibility built into its genetic code, it doesn’t need to evolve to respond. It can adapt quickly. So species with high plasticity have a big advantage in a time of rapid change.

In my book I write about the Humboldt squid, which for decades supported a large-scale commercial fishery in the Gulf of California. Ten years ago, when a series of marine heat waves began coming through, the squid disappeared — or so everyone thought. It turned out that, rather than driving the squid away in search of cooler water, as people assumed, the heat wave had triggered a change in young squid during the larval phase, or maybe even inside the egg. The squid grew at a different rate and matured in half the time, allowing them to continue breeding and reproducing. But they were also smaller — too small to bite the fishermen’s hooks. In the past Humboldt squid were two meters in mantle length [i.e., not including head, arms, and tentacle. — Ed.]; now they were thirty centimeters — a fraction of their former size — but still technically full-grown, still healthy, still reproducing. Their response to that ocean-temperature change was the result of plasticity and has earned them the nickname “plastic squid.”

Other species are much more fragile and cannot adapt that quickly. With coral reefs, for example, there’s a symbiotic relationship between the coral polyps and the algae and so forth that live within them, using photosynthesis to create food that benefits the coral. That symbiosis can only occur within a narrow temperature range. When it gets too hot, they’re like roommates in a stuffy apartment, and they start to fight. The algae, which provide the vivid color of the reefs, get kicked out, and the coral polyps turn white. We call it “bleaching.” They can survive like that for a little while, but coral polyps are lousy feeders. Without their algal partners to provide them with food, the corals eventually die, and you get these ghost reefs that are much lower in diversity and productivity than the ones that came before.

Healthy coral reefs sustain fishing and protect coastlines from erosion. Their inhabitants also provide ingredients for a growing number of pharmaceuticals; they’ve been called the “medicine cabinets of the twenty-first century.” But they don’t have the plasticity of the Humboldt squid.

Leviton: Aren’t researchers studying plasticity in various species?

Hanson: Yes, in part to identify which species and systems need our help the most. There’s so much going on, it can feel overwhelming: What are our priorities? Where will the dollars be best spent? It’s like doing triage. We know the Humboldt squid are going to get through this, but the rodent called the Bramble Cay melomys did not. It is considered the first mammal extinction caused by human-induced climate change. What other species will be unable to adapt?

I wrote in the book about Connie Millar, who studies high-elevation mammals in the Sierra Nevada that are at risk. American pikas seem to have at least a little flexibility because of where they live — talus slopes and rock piles that trap cold air and buffer them against surrounding changes. But there are other species living right next to them — high-altitude chipmunks, for example — that have no way to adapt. We need to learn how the more plastic creatures tick. How does plasticity evolve, and how is it distributed among species? The level and variety of plasticity within a species are probably rooted in both evolutionary strategy and evolutionary history.

To examine strategy, let’s look at the common dandelion, Taraxacum officinale. It grows on every continent outside of Antarctica. It can grow in your driveway, in your lawn, in your flower bed — wherever the seed falls. It can look quite different from place to place but does pretty well anywhere. We would call this a generalist evolutionary strategy.

The opposite is the specialist strategy, where a species becomes the best at just one thing. An example of this is the California dandelion, Taraxacum californicum, which lives only on the edges of wetlands at a certain elevation in the San Bernardino Mountains. It’s very threatened by any change to its climate and is considered endangered.

Specialization is a good strategy when there are long periods of stasis in the environment. You can get a leg up on competitors if you can be the best at doing one particular thing in one particular set of conditions. But when the environment changes fast, those special requirements become a liability, and generalization is more successful.

The other half of the plasticity equation lies in the evolutionary history of a species. When a species has survived for millions of years, it has lived through other periods of change and probably has a lot of prior adaptations still there in its gene pool. All it takes to trigger one — like what happened with the Humboldt squid — is a change in the environment. Then it remembers, Oh, yeah, two million years ago my ancestors adapted to a big change, so I know what to do. Living through a rapid change in the past helps the creature adapt in the present.

Leviton: In your book you give a great example of adaptation by brown bears regarding their dietary choices. Can you talk about that?

Hanson: If you sat down ten years ago with a roomful of biologists and asked them what food was most important to bears on Kodiak Island in Alaska — home to some of the largest brown bears on Earth — the biologists would have said, “Salmon.” There are these incredible salmon runs there, and bears are famous for feeding upon them. It wasn’t until the last five years or so that a team of researchers discovered a very different answer to that question. It wasn’t even the question they had set out to answer.

Leviton: You mention there’s a running joke among wildlife biologists: they are all studying the effects of climate change, but some don’t know it yet.

Hanson: Yes. Biologists are constantly going out into the field now and encountering something different than they expected — different because the climate has changed and so have the lives of the plants and animals they study. So here come these bear biologists, who are curious about how Kodiak bears always manage to be at a particular stream just when the salmon reach their peak, which can happen at different times every year. The researchers had fish traps set up, time-lapse cameras to monitor the streams, GPS collars on about forty bears to follow their movements. Things were going as planned until, right in the middle of their field season, all the bears disappeared. Because the research teams were counting salmon, they knew the bears hadn’t left because of a sudden lack of fish. Using the GPS collars, the researchers were able to follow the bears up onto the ridges and found that they were eating berries — and not just any berries, but the Pacific red elderberries of coastal Alaska. Most berries you find in nature are sweet and starchy, full of carbohydrates and sugars. Everyone knew bears would eat such berries in the fall, when the salmon runs were tapering off and those starches and sugars would help them put on pounds before winter hibernation. Bears like carbohydrates — there’s a reason they turn over garbage cans to get the pizza crusts and pasta.

If you give bears a buffet of their preferred foods, they will choose about 17 percent protein and eat the rest in carbs. Salmon is 70, 80, 90 percent protein — way more than bears need. It has some fat, too, and if there are a lot of salmon around, you might see a bear eat the fatty parts, the skin and belly and brain, and throw the rest away. It’s trying to get more than just protein out of the catch. This makes total sense when we think about the effect of high-protein diets on humans: you can eat a lot of meat and still lose weight, because your body can’t stock away that much protein. The bears have figured this out over evolutionary time; they need to eat more than pure protein if they’re going to put on weight.

Which brings us back to the innocuous Pacific red elderberry. Where most berries are almost pure carbohydrates, the red elderberry contains about 13 percent protein. So it’s very close to the perfect bear food. The bears know this instinctively. Given the choice between protein-rich salmon in the streams and carbohydrate-rich berries with nearly the right amount of protein on the ridgetop, the bears preferred elderberries.

This was brought to our attention by climate change. As the springs and early summers have warmed, the fruiting dates of the red-elderberry bushes have changed. They used to fruit at the end of salmon season; now they fruit right in the middle of it.

When I asked Will Deacy, one of the researchers, how he thought the bears would fare in the future, he predicted that, as long as they can get salmon on either side of the elderberry crop, they’ll actually get even bigger. And a full-grown Kodiak bear can weigh more than 1,200 pounds.

Leviton: What are some other striking adaptations you’ve seen to our rapidly changing world?

Hanson: There’s an Arctic bird called a dovekie in the family that includes puffins. When we think of climate change in the Arctic, we picture the polar bear on the iceberg, drifting around. But if you look past the bear, you’ll glimpse these birds feeding on the rich plankton that exist on the edge of an ice floe. Where melting ice and seawater meet is a good habitat for plankton.

The challenge for the dovekie, which scientists have long believed will decline or even disappear due to climate change, comes during the breeding season. Dovekies don’t nest on ice; they nest on dry land. So as the Arctic ice recedes farther and farther from their nesting colonies, the dovekies have farther and farther to fly to find food to bring back for their chicks. The prediction has always been that eventually that distance will become too great, the chicks will starve, and the dovekie population will crash.

Several years ago an international group of scientists, including the French researchers Jérôme Fort and David Grémillet, went to Franz Josef Land, an archipelago in the Russian Arctic National Park, to study the dovekie. They tagged birds in a dovekie colony with devices that tracked their movements, and they were astounded when they got the first batch of data back. They knew where the ice was and figured the birds would have to be in the air for at least an hour round trip to get food. But the tracking devices said the birds had been in the air for a total of less than four minutes.

Fort told me it was one of the greatest moments of his scientific career, because it was so unexpected. Once again climate change altered the focus of researchers’ inquiries. They began investigating where the dovekies were getting their food. Fort and Grémillet remembered climbing a nearby mountain with Russian scientists the week before. Looking out over the fjord, they could see blue glacial meltwater from the island running into the dark, cold waters of the Arctic Ocean — just a line of it, right out there at the edge of the fjord. They realized that kind of abrupt transition from one kind of water to another is like a death zone for plankton. They come swimming along merrily and hit this curtain of water with a very different temperature and density. They’re stunned at first, and if they stay there too long, they’re going to die. The researchers got into a dilapidated dinghy with a cranky outboard and managed to sputter out to that line, and there were the dovekies all around them, diving and stuffing themselves with plankton.

So they spent the rest of their season studying how the dovekies, once thought to be on their way to extinction, were in fact thriving on their new food source. It’s another example of how quickly a species can pivot, and how unpredictable situations in nature can be. You have to get out and see what’s happening in person, because you might be surprised by what you find.

It also underscores an important theme for any creature trying to adapt to this new world, which is: if you can find a way to get by, either by moving or changing your food source, you’re buying yourself time to find other ways to adapt. In this particular archipelago, those dovekies have bought themselves a century, maybe two. There are a lot of glaciers left to melt.

Leviton: Tell me about the “hurricane lizards” of your book’s title.

Hanson: The lizards give us something we haven’t talked about yet. The squid displayed a plastic response to climate change. The dovekies and bears saw opportunities to change how they satisfied their dietary needs. But none of them had to evolve in the classic Darwinian sense. Evolutionary ecologist Colin Donihue studies a lizard in the anole family, related to iguanas and chameleons, that lives on the Turks and Caicos Islands. What happened with the lizard amounted to measurable evolution — inherited genetic change — over a very short period of time.

Originally Donihue and his crew had surveyed the lizards as part of a project to eradicate some invasive, nonnative rats that were preying upon the lizards and other native island fauna. They planned to return in a year, after the rats were gone, to see how the lizard population was doing. But then two major hurricanes struck back-to-back: Irma and Maria. They leveled the place, uprooted trees, knocked over buildings, and left the human and animal populations reeling. The rat study was put on hold. But Donihue, who had gathered a lot of data on the lizards before the storms, recognized that he was in the rare position of being able to study the effect of the hurricanes on the lizards. He cobbled together some research funding, returned to the islands, and began catching and measuring lizards all over again. And he started to see that the post-hurricanes population was measurably different. It wasn’t that the lizards had changed their bodies in six weeks, but the survivors all shared a suite of traits that had helped them get through the storms. They had larger toe pads, longer and stronger front legs, and shorter back legs, compared to the population before the hurricanes.

Colin and his team wondered what the lizards had actually done in the middle of a hurricane, so they decided to re-create high-wind conditions using a leaf blower. They would put a lizard on a stick, similar in size to the branches it was used to, and then begin turning up the blower. The lizard first went to the lee side of the stick to get out of the wind. As the speed increased, its back legs slipped off the stick. The whole back part of its body was flapping like a flag in the wind. In that situation it was an advantage to have those big, sticky front toe pads and longer, stronger front legs for gripping. And with shorter back legs, there was less drag, and the lizard could hold on longer.

In the course of a single field season the nature of the lizard population had changed significantly. The next step was to see if the survivors passed on these traits to the next generation. And, sure enough, those traits were handed down. But that’s still not enough to indicate evolution in action. In nature traits can “wobble” around some average over time, meaning, OK, you had a couple of big hurricanes, and you now see big toe pads, but if you don’t see another hurricane in that area for a hundred years, will the toe pads get smaller again? The only way to test would be to have more hurricanes, but you can’t just order one on the phone.

Colin teamed up with a meteorologist, and together they mapped the history of hurricanes across the Caribbean. Then they examined lizards across the entire area, plus museum specimens from before those populations were born, and they discovered that wherever there were frequent, major hurricanes, those characteristics Colin saw in the Turks and Caicos survivors showed up in the lizard population. In this instance, the climate-driven increase in hurricanes is changing the evolutionary history of those lizards.

Leviton: We haven’t yet talked about “refugia,” a term coined for places where species find shelter when conditions become unfavorable where they normally live.

Hanson: You can see small versions of this in any landscape. Right now I’m looking over a hill on the southern tip of the island where I live. The prevailing winds come from the south, making the south side of the hill drier. The southern sun hits it all summer long. Grass is the only thing that’s going to grow there. But on the north side of that same hill is a dense Douglas-fir forest. Trees can’t survive where it’s dry and windy, but introduce shade from the hill to keep things moist, and you’ve got trees. In the future, as it gets warmer, the north side of the hill might serve as a refuge for other creatures and plants that need a cool, moist place.

We might find refugia in a deep canyon that stays out of direct sunlight, or the shady side of a tall mountain. A few species might be saved in these places, but we can’t rely on refugia as a solution, because they are too spotty. If overall temperatures don’t cool, we’ll be stuck with these very tiny, at-risk populations. But if we get our act together and ease global warming, these refuges might preserve species long enough to serve as nurseries, helping to repopulate surrounding areas that become habitable again.

Gretta Pecl of the University of Tasmania, a leader in the study of wildlife range shifts, told me something I try to keep in mind: “If a species can move in response to climate change and survive, that is a good outcome.” It’s a nice reminder for biologists and backyard nature enthusiasts alike: it can be traumatic to see changes in our environment, and there may be once-common species that we don’t see any longer, but if they have been able to shift their range or find refuge and survive, at least it’s not a tragedy. You might miss seeing that bird in your yard, but if it’s doing well somewhere else, good for it.

Leviton: What about humans’ response to climate change? How are we doing?

Hanson: We are using basically the same tool set to respond as other animals: Will we move, adapt, or die?

When Hurricane Ida hit New Orleans in August 2021, the question was “Will the new seawall continue to hold?” It had failed during Hurricane Katrina in 2005 and flooded great areas of the city. The rebuilt walls held. It was an example of successfully staying where you are and adapting. We used the great plasticity provided by the human brain, our ability to build things and alter the landscape.

In 2021, however, the seawall was protecting a New Orleans population that is still 20 percent smaller than it was before Katrina. That population loss is an example of moving as a response to climate events. More than a quarter million people left New Orleans, many deciding that its climate wasn’t for them anymore. They shifted their range, if you will.

Leviton: Why are we not treating climate change as a dire emergency? How do we get motivated?

Hanson: Unlike any other species on the planet, we can do more than react to climate change. If we choose to, we can alter the systems and habits that are causing it to happen. We’ve been very reluctant to do so, and I think part of that has to do with how we’ve often talked about climate change as something geographically distant, something happening far away in places like the Arctic. We might think, Poor polar bears, but we can get along without them perfectly well. And we talk of the worst effects happening far in the future, so it’s distant in time as well. Only recently have people begun to perceive the climate crisis as a more visceral, immediate threat.

I was on a panel with a woman who studies polling data, and she said the increasing frequency of extreme weather events — the droughts, the fires, the floods, the hurricanes, the weird snowstorms, the freak weather — is starting to help people see the connection between climate change and their own lives.

Leviton: People don’t care about the climate, but they care about the weather.

Hanson: [Laughs.] Yes, climate is what you expect, and weather is what you get! When you have a heat dome like we had here in the Pacific Northwest in 2021, with hundreds of people dying and millions of mollusks literally getting cooked alive on the beaches at low tide, citizens start to respond.

Ultimately climate change has to matter enough to people to influence the way they vote, the way they live, the daily decisions they make. I take some hope from the polling data. A Pew study showed 54 percent of Americans now view climate change as a major threat to the country. That’s a start, and I hope it will drive more-rapid policy changes.

The 2022 Inflation Reduction Act was the first significant climate legislation since 2007. We didn’t get everything we needed, but it was still far more than we had gotten before. So things can change, and I think the change will be driven from the bottom, by the citizens. We tend to think change will be top-down, that we need new leaders, new legislation, new policies. And we do. But the demands have to come from the constituents. We need a cultural shift in our relationship to energy — not just how we produce it, but how much of it our lifestyles demand.

Leviton: You seem optimistic about how many years we have before it’ll be too late to stop catastrophic climate change. Are you?

Hanson: I’m not always optimistic. I have my down days, too. But I’m very stubborn, and I’ve found being stubborn on these issues carries me through to the next moment of hope. That’s my Norwegian half speaking there. [Laughs.]

Let me answer that question with an old Norwegian joke: Elderly Ole lived on a farm in North Dakota. When he was on his deathbed, everyone in the family gathered to say their final goodbyes. Ole looked up and asked, “Is Lena here?” And they said, “Yes, Lena’s here.” Ole said, “Is Carl here?” And they told him yes, Carl was there. He went through the whole family, getting more worked up with each name.

Finally someone said, “Ole, calm down. The whole family’s here with you.”

And Ole said, “Then why is the light on in the kitchen?”

Leviton: [Laughs.] I can relate to that.

Hanson: I like what the joke says about our relationship to energy. In the modern era we’ve become accustomed to cheap and ubiquitous electricity, but when power lines first reached rural communities, those farmers treated it as a rare and precious commodity.

The type of relationship we need to develop with energy will be an act of remembrance as much as an act of learning. We need to think about energy more like Ole. If we can do that, we can reduce emissions and still enjoy a fine life on this planet.