As the Earth heats up, animals and plants are not necessarily helpless. They can move to cooler climes; they can stay put and adapt as individuals to their warmer environment, and they can even adapt as a species, by evolving.
The big question is, will they be able to do any of that quickly enough? Most researchers believe that climate change is happening too fast for many species to keep up. (Related: "Rain Forest Plants Race to Outrun Global Warming.")
But in recent weeks, the general gloom has been pierced by two rays of hope: Reports have come in of unexpected adaptive ability in endangered butterflies in California and in corals in the Pacific.
Two isolated reports don't, of course, diminish the gravity of the global threat. But they do highlight how little we still know about nature's ability to cope with climate change.
"Most of the models that ecologists are putting out are assuming that there's no adaptive capacity. And that's silly," says Ary Hoffmann, a geneticist at the University of Melbourne in Australia and the co-author of an influential review of climate change-related evolution. "Organisms are not static."
Nature on the Move
That species are on the move is becoming obvious not just to scientists but also to gardeners and nature-lovers everywhere. Butterflies are living higher up on mountains; trees are moving north in North America and Europe. In North Carolina, residents are still agog at encountering nine-banded armadillos, which have invaded the state from the south.
A 2011 review of data on hundreds of moving species found a median shift to higher altitudes of 36 feet (11 meters) per decade and a median shift to higher latitudes of about 10.5 miles (17 kilometers) per decade.
There's also a clear warming-related trend in the timing of natural events. One study suggests that spring shifted 1.7 days earlier between 1954 and 2007. Insects are emerging earlier; birds are nesting earlier; plants are flowering and leafing out earlier. The latest of such natural events studies, out last month, shows that climate change has stretched out the wildflower bloom season in Colorado by 35 days.
The report last month from a butterfly conference in England was a bit different, however. It concerned the endangered quino checkerspot butterfly (Euphydryas editha quino), well known for being threatened by climate change. Many experts believed the species was doomed unless humans collected the butterflies and moved them north; their path to higher ground seemed to be blocked by the megalopolis of Los Angeles.
But at the conference, according to an account in the Guardian, Camille Parmesan of the Marine Sciences Institute at Plymouth University in the U.K., who has studied the quino checkerspot for years, reported that it had miraculously shifted its range to higher altitudes. Furthermore, it had somehow learned to lay its eggs on a new host plant.
"Every butterfly biologist who knew anything about the quino in the mid-1990s thought it would be extinct by now, including me," Parmesan told the Guardian. (Parmesan confirmed the account for National Geographic, but declined to elaborate until she could publish her own research paper on the subject.)
Resilience in Corals
Another uplifting tale of unexpected resilience appeared in Science on April 24. While surveying the waters of the future National Park of American Samoa off Ofu Island, researcher Peter Craig noticed isolated coral pools that were considerably warmer than the rest. High water temperatures can cause corals to "bleach": They spit out the photosynthesizing algae that live inside them, thereby losing both their color and their means of collecting energy. Yet these particular corals didn't seem to be suffering too much from the heat.
Marine ecologist Stephen Palumbi of Stanford University in California tested the heat tolerance of some of the Acropora hyacinthus corals from unusually hot pools. He plopped them into a container, then cranked up the heat inside to 34 degrees Celsius (93 degrees Fahrenheit) for three hours. Just 20 percent of the individual coral animals spit out their algae, whereas 55 percent of coral from an otherwise similar but much cooler pool spit out their algae during the test.
The more revealing test came next. Palumbi took corals from the cool pool and put them in the hot pool. One year later, he measured their heat tolerance—and found it had greatly improved. The heat stress test caused only 32.5 percent of the transplanted corals to spit out their algae, instead of 55 percent.
Palumbi's experiment helped tease out the two different mechanisms by which organisms can adapt. Individual transplanted corals were able to adapt to the hotter water, without any change in their genes. Biologists call that phenotypic plasticity.
But the transplanted corals were still not as good at taking the heat as corals that were native to the hot pools; 32.5 percent of them bleached during the stress test, compared with just 20 percent of the hot-pool natives. That gap might reflect the operation of another mechanism of adaptation: genetic evolution. Over many generations, natural selection may have changed the genes of corals in the hot pools by allowing the most heat-tolerant ones to survive and produce more offspring.
For the Samoan corals in a warming ocean, the combination of plastic adaptation and genetic evolution could be "the difference between dead and more or less unfazed," Palumbi says. The results suggest to him that previous predictions of extinction for all coral might be a bit too pessimistic.
More generally, such individual stories of adaptive ability suggest that the quality of resilience has been left out of our models and predictions about how the natural world will respond to climate change. "I do think there is more hidden adaptability out there," says Palumbi.
Snails, Salmon, Owls, and Thyme
So far, evidence of adaptability is available for only a few species. Juha Merilä of the University of Helsinki in Finland, who edited a special issue of the journal Evolutionary Applications in January rounding up the evidence for such changes, guesses that there are perhaps 20 studies robustly linking adaptation through phenotypic plasticity to climate change, and another 20 or so clearly linking climate change with genetic evolution. But, he says, it's likely that this is a tiny fraction of the species in which adaptation is occurring.
There are better data on shifts in ranges and the timing of events, thanks in part to citizen science efforts like Project Budburst and the Great Backyard Bird Count. But these studies don't prove whether the shifts are due to plasticity or genes, or even that climate change is the underlying cause—they're just highly suggestive correlations between rising temperatures and the location and behavior of species.
Among the most solid examples of actual evolution in response to climate change is a shift in the proportion of European larger banded snails (Cepaea nemoralis) with light colored shells. Shell color is genetic, and the genes responsible are known. It has been shown that, in a given environment, snails with light colored shells have a lower body temperature than those with dark colored shells. And light colored shells are becoming more prevalent over time in the Netherlands, even in wooded, shady environments where you might expect dark shells to dominate.
A few other studies have caught species actually evolving in response to climate change. Pink salmon in Auke Creek, Alaska, which is heating up .03 degrees Celsius (.054 degrees Fahrenheit) per year, are now migrating out of the creek earlier, and scientists have shown that that change is genetic.
Wild thyme (Thymus vulgaris) in France has evolved in response to fewer extreme cold events since the 1970s, producing more pungent oils to deter herbivores (at the cost of becoming less cold-hardy).
Tawny owls (Strix aluco) can be light gray or brown, depending on the genes they inherit from their parents. As snow cover in Finland has declined since the late 1970s, the light gray owls, best camouflaged during snow, no longer have much of an advantage, and scientists have shown that brown owls are now much more common.
Such studies require patience. "It is really hard to get the evidence because you need long-term studies and it is very hard to make science over these kinds of periods," says Merilä. The snails have been studied for at least 45 years, the owls for 36, and the salmon for 32.
And such studies also leave unresolved how one ought to feel about these subtle transformations. When we see spring springing earlier or snails changing color, should we mourn the changes as sad, human-caused degradation, or embrace them as evidence of plucky nature fighting back? "A bit of both," says Hoffmann. "We have to accept that things will change."
"I think we should feel impressed by the impact that we have, that we can change the course of evolution around us by the way we change the environment," says Menno Schilthuizen, who studies how invertebrates adapt to climate change at the Naturalis Biodiversity Center in Leiden, Netherlands. "Our impact is much further and deeper than we tend to think."
Some Will Die
Researchers on this topic are quick to point out that evolution and individual plasticity won't save all species. Climate change is happening too fast, they say, for some species to survive.
Hypotheses abound on which species are likely to keep up with climate change. Species with short lives, like fruit flies, have more generations in which to evolve, compared with long-lived species that don't begin to breed for decades. And some species, like some conifer trees, simply have more gene variants to work with in their populations.
Conversely, long-lived species with low genetic variability—including many rare mammals—will have less adaptive ability. "In general, you might expect that weedy, short-lived species and ones that are able to disperse widely might be favored," says Steven Franks, who studies how plants adapt to climate change at Fordham University in New York.
There's also a widespread but still poorly tested hypothesis that tropical species may have a harder time evolving than temperate species do. Having evolved in a region with less climate variability over both the years and the millennia, tropical species may harbor a less diverse set of genes related to heat tolerance and similar traits. "The tropics are hot, but they are not particularly variable," Hoffmann says. "It is not like they are being challenged all the time."
Predicting which species will survive on their own can help researchers zero in on which species might benefit most from human help. A key goal of such an intervention would be to bring back genetic diversity to small, isolated populations so that evolution has something to work with. "Where we have a fragmented landscape, we should connect it up again, restore the flow," says Hoffmann. "We are restoring a process, and that process is really powerful."
Where it's not possible to connect fragmented populations with contiguous habitat, "restoring the flow" could mean moving seeds or individuals from population to population. In dire cases, Hoffmann says, conservationists might want to create hybrids of two related species or subspecies, if each one is insufficiently able to adapt on its own. "People think 'genetic pollution!'" he says. "But you could achieve a lot in terms of saving these populations."
Palumbi, meanwhile, thinks the adaptability he found in Samoan corals won't save them as much as provide a grace period; eventually, he says, human-made climate change could outstrip the corals'—and many other species'—ability to adapt.
"That delay of a couple of decades is the good news here," he says. "Let's use the decades to solve the problem." And when he says "the problem," he means the root of the problem: carbon emissions.