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MICHELE NORRIS, host:

From NPR News, this is All Things Considered. I'm Michele Norris.

ROBERT SIEGEL, host:

And I'm Robert Siegel. There is some sobering news to report today from a new study on climate change. There is no going back. Climate change is essentially irreversible. The study says as carbon dioxide emissions rise, the world will be committed to more and more long-term environmental disruption. And the damage will persist even if and when emissions are brought under control. More now from NPR's Richard Harris.

RICHARD HARRIS: Susan Solomon is one of the world's top climate scientists, and the more she studies global warming, the more it becomes evident to her that this is not just another pollution problem.

Dr. SUSAN SOLOMON (Climate Scientist, National Oceanic and Atmospheric Administration): We're used to thinking about pollution problems as things that we can fix, you know, smog, we just cut back and everything will be better later. Or haze, you know, it'll go away pretty quickly.

HARRIS: That's true for some of the gases that contribute to climate change, such as methane and nitrous oxide. But as Solomon and colleagues now show in a new study published in the Proceedings of the National Academy of Sciences, it's not true for the most abundant greenhouse gas - carbon dioxide.

Dr. SOLOMON: People have imagined that if we stopped emitting carbon dioxide that the climate change would go back to normal in maybe 100 years, 200 years. What we're showing here is that's not right. It's essentially an irreversible change that will last for more than a thousand years.

HARRIS: That's because right now the oceans are soaking up a lot of the planet's excess heat and a lot of the carbon dioxide we're putting into the air. Even assuming we could stop putting carbon dioxide into the atmosphere, that would not solve the problem. Carbon dioxide will eventually start coming out of the ocean, and the heat will come out too. And that will take place for many hundreds of years.

Solomon is a scientist with the National Oceanic and Atmospheric Administration. Her new study looked at the consequences of this long-term effect in terms of sea level rise and drought. If we continue with business as usual for just a few more decades, she says those emissions could be enough to create permanent dust-bowl conditions in the U.S. Southwest and around the Mediterranean.

Dr. SOLOMON: The sea level rise is a much slower thing, so it will take a long time to happen, but we will lock into it, based on the peak level of CO2 that we reach in this century.

HARRIS: The idea that changes will be irreversible has consequences for how we should deal with climate change. We can't turn down the global thermostat once it's been turned up, so scientists say we need to proceed with more caution right now. Michael Oppenheimer is at Princeton University.

Professor MICHAEL OPPENHEIMER (Geosciences, Princeton University): These are all, by the way, changes that are starting to happen in at least a minor way already. So the question becomes, where do we stop it? When does all this become dangerous?

HARRIS: The answer is sooner rather than later. Scientists have been trying to advise politicians about finding an acceptable level of carbon dioxide in the atmosphere. The new study suggests that it's even more important to aim low. If we overshoot, the damage can't be easily undone. Oppenheimer feels more urgency than ever now to deal with climate change, but he says, in the end, setting acceptable limits for carbon dioxide is a judgment call.

Prof. OPPENHEIMER: That's really a political decision because there's more at issue than just the science. It's the issue of what the science says, plus what's feasible politically, plus what's reasonable economically to do.

HARRIS: Now, it might be tempting throw up your hands at this point and say, forget it. If changes are irreversible and emissions are already running out of control, the situation is hopeless. But Susan Solomon doesn't see it that way at all.

Dr. SOLOMON: I guess if it's irreversible, to me it seems like all the more reason that you might want to do something about it. Because committing to something that you can't back out of, seems to me like a step that you'd want to take even more carefully than something that you thought you could reverse.

HARRIS: To her, that's means stepping up action to prevent the situation from getting much worse than it is already. Richard Harris, NPR News.

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