Why We Can't Count on Evolution to Counterbalance Climate Change

New study suggests animals need an average of one million years to adapt to a single-degree increase in overall temperature

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A polar bear mother and her cub.
A polar bear mother and her cub. Jon Cornforth/Barcroft Media/Getty Images

Many adults remember middle-school lessons about England's peppered moth – a popular, easily understood illustration of the principle of natural selection. Most of the moths were once white, perfectly camouflaged to hide amid lichen and light tree bark; once the Industrial Revolution began, however, the lichen died off and the trees became dark with soot. The common light moths became easy pickings for predators, while rare, darker ones hid and flourished. When air quality standards improved, white-bodied moths became common again.

Stories like this feed our impression that evolution is a relatively quick process – that animal and plant species are readily equipped to adapt to whatever humans throw at them. I've heard this idea directly in conversations about climate change: Humans will just use more air-conditioning, and everything else will just evolve. No big deal.

The truth, unfortunately, is less comforting. A new study published in Ecology Letters found that the rate of climate change forecast for the next century is a bit more than vertebrate species are used to coping with via evolution. How much more? Try a factor of 10,000 times or more.

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The study's authors looked at the evolutionary histories of 270 closely related pairs of species, including birds, reptiles, mammals and amphibians. They compared how long it's been since the paired species diverged from a common ancestor with changes in temperature and rainfall in their climatic niches, and found a common pattern: In general, it took the species about one million years to adapt to 1°C of temperature change. In contrast, current models of our changing climate anticipate as much as 4°C of warming by 2100. (Precipitation changes were somewhat more varied, but for both factors, historical evolution happened 10,000 to 100,000 times more slowly than currently predicted rates of climate change would demand).

The authors listed a number of caveats to their conclusions, including a relatively small sample size. And, of course, there are ways that species can survive a changing climate besides physical evolution. Populations may move closer to the poles or to higher elevation; they may make behavioral adaptations; they may become more stressed, but muddle through. And the absence of rapid adaptation to temperature changes in the past doesn't necessarily preclude future adaptation (though none of the species studied had evolved much faster than the one-degree-per-million-years average).

But the point remains: The rate of climatic change that our past and current greenhouse gas emissions will create is not business as usual. It's not anything like the natural dynamism of the geologically recent past – you know, the one in which human civilization, not to mention many of the species with which we share this planet, happened to evolve. It's not the kind of problem we can ignore and hope that a little light adaptation will fix.