Previous Eras of Warming Hold Warnings for Our Age

By 2100, the world will probably be hotter than it’s been in 3 million years. In an interview with Yale Environment 360, paleoecologist Anthony D. Barnosky describes the unprecedented challenges that many species will face in this era of intensified warming.\"audio\"

The earth’s climate has, of course, fluctuated frequently — and at times wildly — over hundreds of millions of years, long before humans began pouring heat-trapping gases into the atmosphere. So why the concern over the current surge of warming, brought about largely by human activity? Anthony Barnosky, a University of California, Berkeley, scientist who has studied previous eras of climate change, succinctly sums up the problem: Too much warming, too fast.

In his new book, Heatstroke: Nature in an Age of Global Warming, Barnosky lays out his concerns that the planet’s fauna and flora — hemmed in by 6.5 billion people and facing steadily rising temperatures — will

Anthony D. Barnosky
simply not be able to keep up with the pace of change, leading to large-scale extinctions. In previous periods of warming, when the earth moved from glacial to interglacial periods, temperatures have risen by 5 degrees C (9 degrees F) in the course of several thousand years. But, Barnosky explains, it is entirely possible that unless something is done to rein in greenhouse gas emissions, the planet could experience that magnitude of warming in a century or two.

Speaking with science writer and Yale Environment 360 contributor Carl Zimmer, Barnosky describes the scope of the threats that lie ahead and some of the steps that can be taken to save as many species as possible.

Yale Environment 360: In your book, you look at the current global warming we’re experiencing and put it in the context of climate change that the earth has experienced over millions of years. Could you tell us how global warming that’s happening now compares with the warming in the past, like when the earth has come out of ice ages?

Anthony D. Barnosky: Sure. There’s a short answer to that, which I’ll give you first. Today is too much and too fast. And the longer answer is why. If you look at how temperature has changed over the course of the earth’s past, you see it changing actually over time, on all different time scales. From day to night, to what happens over millions of years.

And the kind of climatic changes that paleoecologists and geologists talk about really take place on a couple of different time scales. There’s the tectonic time scale, where you see very slow drifts of a few degrees over a few million years. And then there’s the ice ages, which are much more dramatic. Those are the ones that are really more analogous to what we’re seeing today, as to how much the temperature warms and cools.

There were about 39 changes from glacial times to interglacial times over the last couple of million years. And with each cycle, we see a temperature swing of about 5 degrees C, which is similar to the magnitudes being
Listen to the full interview (31 min.)
predicted with today’s global warming. So in that sense and magnitude, really not too different from things that have taken place in the past. The big difference, though, is how fast we’re making that happen. And of course that people are making this one happen. And that we’re already starting in a hot time.

So when we talk about swings of 5 degrees C in the past, we’re talking about going from a time when it was so cold that ice came down and covered a good part of the North American continent, to times like today. So we’re going from a very cold time, glacial, to a time we consider as normal. That is the interglacial we’re in today.

That 5 degree change takes about a couple thousand to 5,000 years. The reason that what is happening today is different is because we’re starting out in a hot time and we’re raising the temperature from that hot base to a hotter base, and we’re doing it much faster. We’re going to see temperature changes like what we had between glacials and interglacials happening over the course of decades, to maybe a century or two.

e360: You’ve spent about 20 years investigating how climate change has affected life in the past. What would you say were some of the big lessons that you’ve learned from this research about the relationship between climate and diversity and extinctions?

Barnosky: I think there’s good news and bad news in that. And the take-home lesson probably is that nature has a speed limit when it comes to how fast she can respond to big changes. The good news part of that story is really that species in ecosystems tend to be pretty resistant to changes. Species tend to persist through “natural” climate changes. Oftentimes ecosystems tend to hang together, at least in the way the species are interacting as you go across these naturally occurring climate changes.

And all that makes sense when you realize that species in ecosystems are evolving on that background of constant change. If they couldn’t withstand those kinds of natural changes, then obviously they’d go extinct in pretty short order.

So the bad news is that when species in ecosystems experience more pressure than that natural background rate that they’ve evolved to withstand, they tend to snap pretty catastrophically. For species, that can mean extinction. For ecosystems, that can mean a wholesale change — different compositions of species, different ways that they interact, just a very different-looking landscape.

So it’s that sort of breaking point we could be approaching now. As an example of that, I can talk a little bit about what happened the last time similar sorts of things came together. That is, a dramatic global warming event from the last glacial into our present warm time, about 10,000 or 12,000 years ago.

That was at the same time that we had expanded numbers of people rapidly populating new continents on earth. What happened then, when those two things came together — which is in broad-brush form analogous to what’s happening now — is a dramatic extinction event. Half of the large mammal species on earth went extinct at that time. That’s an example of the global ecosystem snapping and going into a new state.

e360: In your book, you talk about these wonderful animals called the Irish elk, which were deer with these huge antlers. They were one of the victims of this period of extinctions. Could you talk about some of the things you discovered about how the Irish elk disappeared in this time of climate change?

Barnosky: Irish elk are a very interesting story, actually, in regards to climate change because they give us a very nice analogy for what’s going on today.

First thing about Irish elk is they really were magnificent animals. They had antlers, and like all deer they re-grew their antlers every year. But the antlers were enormous. They were 12 feet from tip to tip. That requires a tremendous amount of nutrients to go into the body each year and be converted into antler.

Now they were distributed very widely throughout Eurasia. If you look at what happened to them in Ireland versus what happened to them throughout their broader range, something very interesting comes out. Ireland is an island, and the analogy there is most of the places where we’re trying to preserve species today are in fact islands of nature surrounded by disturbed habitats.

About 12,000 years ago, as we went into this global warming event that took us from this last glacial into the present interglacial, Ireland and the
“We really are seeing the disappearance of whole ecological niches, which means extinctions.”
northern latitudes as a whole actually got cooler. So one point to make here is that just because you have global warming, it doesn’t get warm immediately everywhere. Climate changes, but in this case it actually got cooler. And the reason is because there was a flood of fresh water into the North Atlantic, which changed the oceanic circulation that actually keeps northern latitudes a little warmer than they would be otherwise.

With that cooling event, vegetation in Ireland couldn’t support these Irish elk anymore and they rapidly went extinct there. Now in other parts of their range where they could just simply move in response to the climate change and find a favorable habitat, they were able to hang on much longer, finally going extinct around 7, 000 years ago.

e360: Climate change is not something that’s going to just have effects in the future, but man-made climate change is already starting to have an impact now. What are some of the most important changes?

Barnosky: We’re seeing a lot of things over the past few years that are giving ecologists cause to worry. I think probably the biggest cause for worry is we really are seeing the disappearance of whole ecological niches, which means extinctions.

Think of what’s happening with polar bears. As the Arctic melts, their range dramatically decreases, and they’re basically on the way out. The same thing is happening with several species that tend to live at the cool tops of mountains. As those mountaintops heat up, they get too warm and dry to support the species that have been adapted to live in those places, and those species are disappearing because their ecological niches are disappearing. An example of that are pikas in the southwestern U.S.

So there’s individual species effects, but not too far into the future I think we have to worry about the disappearance of whole ecosystems, as well. Places like the Everglades, a very unique ecosystem on earth, are going to be mostly underwater. Coral reefs, one of the most important ecosystems on earth — the rainforest of the sea, so to speak — are being affected as waters warm just a little too much. Corals are bleaching and dying.

e360: Sometimes people will say that we don’t need to worry about global warming because it has been warm in the past, and that paleoecologists like yourself can show us that there were plenty of animals and plants thriving at these warm temperatures. And so therefore we don’t need to worry. What do you say to those skeptics?

Barnosky: I would say they’re absolutely right, there were a lot of different species on earth on then, but none of those species were human beings. [laughs] And in fact by the 2040s or 2050s, earth is going to be hotter than it has ever been since human being evolved, if we keep going without mitigation to slow greenhouse gas emissions.

By the year 2100, earth will be hotter than it’s been in 3 million years. Three million years ago, probably not one species that you’re familiar with on earth today was alive. So, yes, there were species, there will be species in the future, but the problem is that the earth that people have adapted to and are familiar with will be very different in the future. We will be outside the bounds of anything humanity has ever experienced.

The problem is that the warming is so fast that the normal response of species to climate change really is just to move, and species can only expand or move their geographic range so fast. They’re limited by generational time — how long does it take to produce offspring, what kind of dispersal, how do they actually move around the landscape.

The rate at which climate is changing means that species are not going to be able to get to their new climate zone, at least a lot of species, even if there were suitable habitats to migrate through. Which for the most part there are not, because the species that we’re interested in protecting often are in nature reserves that have these very hard boundaries around them. So that’s where rate becomes a problem.

e360: And then the other issue is that there are billions of people on earth, and they’re affecting how the ecology can respond to climate change, too. So what do you see as the big ways that a whole lot of people on earth change the equation?

Barnosky: That’s where you need to worry about how global warming interacts with these other problems. I define this a a gang of four, of which global warming is one part. The other three are habitat fragmentation, invasive species, and growing human populations. You put those all together and it means that nature as we know it really is in trouble, because there’s really no way that a lot of species are going to be able to survive unless humanity consciously makes an effort to save them.

e360: When you look forward, are you optimistic or do you feel like we’re going to have to just deal with maybe even moving species just to cope with a global warming that’s inevitable? How do you feel about the future as a scientist?

Barnosky: Well, you know, I’m optimistic and pessimistic depending on my day. But overall, I think there’s still a lot we can do. So I’m optimistic.

Let me start with the pessimistic part. Here’s what I think we’ll see if we don’t take the right kinds of steps. I think we’re going to see a major reduction in world biodiversity. Right now we’re actually in fairly reasonable shape. We’ve got about 12 percent of the land surface actually legislated to save aspects of nature, mostly species or special landscapes. There’s a total of 36 percent of the earth’s land surface that’s lightly populated. And there’s still 70 percent native vegetation. So that’s all very good.

The problem is, those places are distributed around the earth’s surface in patches. So we have these islands of nature, and as we change climate rapidly, the species within those natural areas — which are the areas we have the species we want to preserve for the most part — the species just can’t move from one place to the next, even if they could move fast enough.

So that’s the problem. And what we will see is more and more species going extinct solely because of climate change, if we don’t do something. So what do we do? I think that conservation biologists need to redefine how they do business. There’s some things we’re doing right, but some things we’re going to have to change.

You asked about assisted migration. That’s one of the new approaches, I think, that is on the horizon, that is probably going to be inevitable, and it’s
“We really are seeing the disappearance of whole ecological niches, which means extinctions.”
already beginning to happen, with butterflies, for example. But that simply means you take a species from a place where it’s going extinct because its climate is changing and you move it to a different part of the world, where it has suitable climate to survive. I think we’ll probably be doing some of that to keep species alive.

The danger with that though, is that we can’t really predict how those species are going to interact with the species that are already in that place that we’re moving them to. And then there’s also the issue of what does that really do to preserve all the aspects of nature people care about, one of which is a feeling of wildness in many of these reserves. As soon as you start moving species around, you’re basically constructing elaborate zoos.

e360: There’s been a debate about whether conservation biologists should be focusing on preserving habitat or planning how they’re going to respond to the effects of climate change. Conservation biologists have limited resources, and some people have argued that the focus on climate change is detracting from the work that they can do on something that’s obviously a big threat to biodiversity, which is the loss of forests and other habitats. What do you think of this debate?

Barnosky: I don’t really think it’s an either/or question in terms of preserving habitat or responding to the effects of climate change. The way I’ve framed this solution, in my mind anyway, is a strategy I call keep-connect-and-create. Keep on with a lot of the things we’re doing, like making sure we don’t lose any of these natural areas we have been working to protect for so long. Connect — people already are talking about corridor strategies in trying to implement connections between nature reserves. But now we need to start thinking about that in terms of climate connection corridors, as well, anticipating where climate is going to be favorable for species to migrate through.

And then third is create, and that’s maybe the most important part, because we have to start thinking about what we’re trying to preserve in three different ways.

We’re trying to preserve ecosystem services on the one hand, which, as I said, is what we get back from other species on earth in a very direct way. We’re trying to preserve biodiversity — just keeping species alive on earth that are about to disappear. And then we’re trying to preserve this natural, ecological function — these places that make us feel like we’re connecting with nature on an emotional sense. The problem is that what it’s going to take to preserve biodiversity and ecosystem services — that is, management of landscapes, assisted migration — is exactly the opposite of what it’s going to take to preserve these natural ecosystem functions and wilderness.

So I think where we need to be headed is in a separate but equal set of nature reserves where one set of reserves (does) whatever it takes to preserve species. The other kind of nature reserve is more of a wildlands reserve. These are, in scientific terms, are control plots where we’re just watching how nature unfolds in this new age, and not trying to manipulate it too much.