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Report Documents Climate Change Impact on U.S.

May 28, 2008 at 6:20 PM EDT
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A recently released government report describes the impact global climate change is already having on U.S. farms, wildlife, forests and water supplies. One of the report's lead authors discusses its findings.

RAY SUAREZ: Now, a Science Unit update on climate change’s impact in the U.S. For years, scientists have warned of the long-term dangers of a warming climate on the American landscape.

But a new government report provides a detailed assessment showing how global warming is already damaging our forests, farms, wildlife and water supply.

Some of the key findings include: growing threats of wildfires; drought and insect infestations to western forests; unpredictable and harmful rainfall patterns in regions of the country; and crop failure; and other agricultural problems.

For more on this report, we turn to one of its lead authors. Anthony Janetos is the director of the Joint Global Change and Research Institute at the University of Maryland.

And so often we talk about global warming as a far-off, future problem. How did you determine what was happening now?

ANTHONY JANETOS, Joint Global Change Research Institute: One of the things we did about 18 months ago, when we were chartered to do this report by the U.S. Climate Change Science Program, was assemble a team of about 35 authors from all over the country.

We looked for the best scientists in the different fields that we could find. And the guidance we gave to them was to look at scientific publications that document and data that document what’s happened over the last few decades, what’s happening now, and what are our best expectations for what might happen in the next two or three decades.

We don’t mean to minimize the problems of longer-term changes, changes that will take 100 years or so to play out. What we specifically wanted to look at were consequences of changes in the climate system, and natural resources, and water resources, and agriculture, and forests that were relevant to today’s planning horizon.

We went through over a thousand references, over a thousand papers. We’ve drawn on the best available science, sort of the most comprehensive assessment of the science of climate change impacts that’s been done for the U.S. pretty much over the last decade.

And this is what we found, is that we’re starting to see the impacts of changes in climate in our natural resources and ecosystems today. This is not just a problem for our children; this is a problem for us, as well.

RAY SUAREZ: And you found that, as with polar melting, everything is moving faster than the models had predicted?

ANTHONY JANETOS: I think we’ve seen these results kind of coming in the literature, but having them all in one place really does create, I think, a sense of urgency for us, for those of us who’ve been working on this issue for quite a long time.

I think our sense is certainly that we’re starting to see impacts more rapidly. They’re more widespread. And their magnitude seems to be larger than we might have anticipated even 10 years ago.

Changes now inevitable

RAY SUAREZ: Now, you used -- these may sound like tiny amounts to people who don't follow this, but you use the assumption that there would be 60 parts per million more of CO2 in the atmosphere and that the temperature would go up about another two degrees on average.

ANTHONY JANETOS: Well, that's roughly what -- two degrees might be a little much. That's roughly what would happen over the next three or four decades.

There's a lot of inertia in the climate system right now. There's a lot of heat that's essentially been trapped that will express itself, even if greenhouse gases -- if their emissions are cut, which, of course, we don't know exactly what will happen there yet.

And so what we wanted to do was begin to evaluate the question of, well, what are we going to have to cope with? Which consequences are we not going to be able to avoid, but that we're simply going to have to deal with?

What we hope we've done is establish the scientific baseline by which those kinds of strategies for coping and adaptation can begin to be developed and can be improved.

RAY SUAREZ: Well, just over the past week, you could see forest fires, large forest fires burning in the United States, tornadoes, a higher than average tempo of tornado activity. Are these the kinds of things that you conclude that we'll be seeing?

ANTHONY JANETOS: We've seen changes, especially in both the frequency and intensity of wildfire in forests. We've seen very large pest infestations in forests. And we've seen the beginnings of that in agricultural pests, where the increase in temperatures that we've seen allows the pest to accelerate their life cycle. They grow faster; they eat faster.

That increase in temperature in the summer months also stresses the forest. Those trees are now more susceptible to pests. They're more vulnerable to pests.

Interestingly, especially in forests, warmer winters also enhance these pest infestations, because generally, for many of these insect pests, they're killed off in the winter months by very low temperatures. If you don't get those really cold temperatures for long enough in the winter, the insect larvae over winter, instead of dying, and that infestation is even larger the next time around when spring starts.

RAY SUAREZ: Well, currently some of the fastest-growing places in America are also some of the driest places in America. From the report, it looks like they're going to get drier?

ANTHONY JANETOS: That's a very likely outcome. The precipitation and water supplies are extremely difficult to model and to forecast. All the science is certainly not in; there's a fair amount of uncertainty there.

But the simulations that we've looked at suggest that over the next few decades we'll see an acceleration of a trend that we're already seeing, which is that especially the Western part of the U.S. will continue to dry out. And we could be headed towards some very severe drying conditions in that part of the country.

RAY SUAREZ: This conclusion sort of popped out at me. Even under the most optimistic scenarios, you predicted "profound effects."

ANTHONY JANETOS: We believe that to be true. We're already starting to see them in a wide variety of resources.

The most optimistic scenarios for change in the climate system for the next few decades, frankly, are all very close to one another. And so there's going to be a certain amount of change that we are going to have to adapt to, that this will be part of the overall response portfolio.

RAY SUAREZ: And that increased CO2 concentration, there was a lot talk about the impact on agriculture. I thought CO2 was good for plants.

ANTHONY JANETOS: CO2 is good for plants. An increase in CO2 in the atmosphere will help accelerate plant growth.

But at the same time, the increase in temperatures both has the effect of making water supplies more precarious, so that potentially has a growth impact on agricultural crops.

Many crops are also quite sensitive to the temperature itself. And there are critical periods in their lifecycle where the temperature itself can affect the actual -- how much carbohydrate gets into the seeds and, therefore, the actual quality of the crop itself.

Agriculture is a tricky business. It's very adaptable. We don't know exactly how farmers will respond. We have modeled the physical effects, but not how the people will actually respond to those.

RAY SUAREZ: Anthony Janetos, thanks a lot.