Global warming is already causing measurable evolution in animals

One of my favorite things about science is the way, when you’re on the right track, the information you’re getting forms an increasingly coherent picture. For an example from atmospheric physics, it was predicted that because anthropogenic global warming would happen due to increased greenhouse gasses – increased insulation – then all that extra heat getting trapped in the atmosphere should mean that less heat was reaching the upper layers. That means that as greenhouse gas levels rose, and temperatures followed them, we should also be able to measure a decrease in temperature in the upper atmosphere. Sure enough, that’s exactly what’s happening:

Combined data from three NASA satellites have produced a long-term record that reveals the mesosphere, the layer of the atmosphere 30 to 50 miles above the surface, is cooling and contracting. Scientists have long predicted this effect of human-driven climate change, but it has been difficult to observe the trends over time.

“You need several decades to get a handle on these trends and isolate what’s happening due to greenhouse gas emissions, solar cycle changes, and other effects,” said Scott Bailey, an atmospheric scientist at Virginia Tech in Blacksburg, and lead of the study, published in the Journal of Atmospheric and Solar-Terrestrial Physics. “We had to put together three satellites’ worth of data.”

Together, the satellites provided about 30 years of observations, indicating that the summer mesosphere over Earth’s poles is cooling four to five degrees Fahrenheit and contracting 500 to 650 feet per decade. Without changes in human carbon dioxide emissions, the researchers expect these rates to continue.

With this trend being measurable, climate science deniers now have to answer another question – if the rise in greenhouse gases isn’t enough to trap significant amounts of heat in the lower atmosphere, then why is the upper atmosphere cooling and shrinking? If the rise in temperature is – as some still claim – due to increased solar activity, why isn’t the upper atmosphere even warmer than the lower atmosphere? Shouldn’t the external heat source be causing the opposite trend?

Of course it should. The reality is that over a century of climate science has given us a pretty decent idea of how things work up there, and so the predicted warming has come, along with its predicted effects.

And so that brings us to another predicted result of rising temperatures – that it would have an effect on ecosystems, and that the changing conditions would drive evolutionary change in plant and animal populations. The only question was how quickly they would evolve, and whether it would be fast enough for them to survive. It should not surprise you to hear that scientists have been measuring evolution driven by global warming for a while now, and as with the mesospheric cooling, if the planet’s not warming, and the warming’s not having an affect on ecosystems, then why are all these animals evolving as though that’s exactly what’s happening?

I want to note how this change is actually happening. It sounds almost cartoonish to say that lizards are evolving longer arms and shorter legs so they experience less drag when they’re flapping off a twig like a flag in a hurricane, but of course that’s exactly the kind of adaptation you’d expect in a world where the odds of encountering a strong hurricane are increasing. It’s one of the ways in which evolution tends to actually be pretty intuitive, once you get the hang of how it works.

I figure I’ll quickly go through the other changes for those of you unable to watch the video – In the Gulf of California, Humboldt squids, also known as jumbo squids, are becoming significantly less “jumbo” in response to higher temperatures. Apparently they have a high degree of plasticity in how their phenotype responds to the environment, one generation to the next, and so the population in question has apparently cut its size and life cycle in half. I also like how the video emphasizes that not all species are capable of such dramatic change in so little time.

In the arctic, little auks (also known as dovekies, apparently) historically exploit the intense temperature gradient around melting sea ice to eat cold-stunned plankton that encounter the meltwater. The melting ice has moved that feeding ground from being right by where the auks breed, to an hour away, as the dovekie flies. That’s a lot of extra energy to spend – enough that it could doom the species – so they just… didn’t. They found a different temperature gradient just four minutes away, where the fjord’s meltwater met the ocean, and they’ve been feeding on the cold-stunned plankton there.

As the video goes on to state, this doesn’t mean all species are capable of adapting to climate change. When the average limb length of a Caribbean anole population changes, that doesn’t mean that we’ve got the same number of lizards and they all just have different legs. It means all of the ones with different proportions died. If you lay tens of thousands of eggs at a time, like the squid, then your population can probably bounce back pretty quickly if a few of you adapt to changing conditions. For those of us who reproduce more slowly, a drop in population like that means that it will take that much less to kill off everyone that remains. We’re the only species we know of that has – at least in theory – the ability to adapt our behavior and surroundings before it’s forced on us by disaster. Unfortunately, we also seem to be the only species on this planet that has to deal with ideology and propaganda designed to suppress that ability. This is a fascinating time, from a scientific perspective, and the adaptability of these critters is a good reminder that the end of this is not yet written. We can’t predict all of the changes that will occur as a result of the rising temperature and some of those changes may end up making our own adaptation a little easier, in ways we’ve yet to predict.

A man can dream, anyway…

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  1. John Morales says

    Adaptation and evolution are different concepts.
    I think you conflate them.

  2. sonofrojblake says

    @1 – I think you won’t be able to coherently explain the difference.

  3. says

    Fair point. In terms of human adaptation, yes, I am conflating them in this post. That’s mainly because of the things I mentioned about our ability to change our behavior and environment for conditions that don’t exist yet. Maybe that’s not a good enough justification for the way I wrote about it, but I was trying to link it back to humans and our problems.

    I think the dovekie example is probably more a behavioral change than an evolutionary one, but it’s hard to know – some birds have been changing seasonal habits in response to changing weather, and some have been changing them because those that don’t have died. I also don’t know at what point a population-level behavioral change counts as “evolution”.

  4. says

    @sonofrojblake – There are two versions of adaptation that I’m using in this post. There’s adaptation as in a population’s immediate changes in response to changing conditions, that form the “steps” on an evolutionary path, and there’s adaptation as in humans changing our society and behavior to better deal with the changing climate.

    With the squid, I don’t know whether a return to normal conditions would result in an equally rapid return to their former size, or whether they’d keep their new mode of existence. It could be that what seems like a major change across that population is more akin to the way turtle eggs will develop into different sexes depending on temperature, but the squids do it with body size and maturation rate.

  5. John Morales says


    I also don’t know at what point a population-level behavioral change counts as “evolution”.

    When the genome itself changes.

    But yes, I agree that there very much is a significant evolutionary pressure at hand.

    But the anthropocene has so much accelerated the rate of change of environment that it’s pushing the adaptiveness of the existing genome — and of course we humans are pretty much exempt due to our personal environment being regulated by us. Wild species don’t have that luxury.

    sonofrojblake, I don’t have to. I’m on the internet, as are you.

  6. says

    The one thing I would add is that given how unsettled the definition of “species” is, and the genetic similarity of groups like Darwin’s finches, I guess I’m uncertain how much change is required to count as “when the genome itself changes”. Is there actually a clear definition of how much change counts as “an evolution”? If there is I guess I missed it.

  7. says

    To #6: See

    Genetic change goes on all the time. Behavior change does, too. The dovekie example strikes me as an example of “adaptability” in the sense of” behavior change” (the concept of “ecological amplitude” is helpful here). They like certain critters which are most abundant in certain conditions, and when one grocery store stops carrying them, they discover their favorite product in another store they’d never had to visit before.
    One advantage of the much-maligned biological species concept (which works rather well for sexually reproducing animals) is that the “tipping point” of “species/no-species” is reproductive isolation.
    Also note that in most definitions, evolution means “heritable change over time,” and need not lead to speciation.

  8. says

    Thanks for the breakdown.

    I guess my threshold for “evolution” for the purposes of saying that climate change is causing it, is population-level physiological change. It’s probably not the most accurate – especially with something as flexible as a squid – but it seems like a good “shortcut” for most people, that’s not particularly misleading.

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