Dire Warnings for the Fate of Rain Forests
Air Date: Week of February 19, 1999
New Research at Britain’s Hadley Climate Research Center shows that global warming will bring on changes to weather that could cause rain forests, including the Amazon, to die by the middle of the next century.
CURWOOD: Last year was the world's hottest on record, thanks to the emissions of carbon dioxide and other so-called greenhouse gases. Scientists predict that temperatures will keep climbing and change climates around the world. Until recently, researchers had been putting educated guesses about the effects that the oceans have on the world's weather into the computer models that make these predictions. But now the British Government's Hadley Center for Climate Prediction and Research has found a way to take much of the guesswork out of the ocean's effect. The result: a set of troubling forecasts for future weather patterns throughout the world. Among other things, says the Center's director, Geoffrey Jenkins, is the finding that some of the most important rainforests in the world are in for much less rainfall.
JENKINS: The detailed scenarios, the prediction of rainfall, is not as easy as it is for temperature. So we do have to treat this with a little more caution than some of the other observations. But what we do find in the model is that as you run it out through the next century, then you find quite a sharp decrease in rainfall in several parts of the world, particularly over northern Brazil, for example, some parts of southern Africa, even some parts of Europe and America. And in some of the more extreme cases of changing temperature, coupled with this decrease in rainfall, we find that the vegetation that exists there at the moment would no longer be sustainable. So, what the model says is that parts of the Amazon rainforest will disappear over the course of the next 50 years or so.
CURWOOD: That's a pretty startling prediction. You're saying that the Amazon rainforest will simply disappear in the next 50 years?
JENKINS: Parts of it will no longer be sustainable and will die off, that's right.
CURWOOD: Was this a surprising result?
JENKINS: It was indeed. And as I said before, I wouldn't want to claim over- much in terms of confidence in this. But it is a scenario that comes from what we believe is a good model. And therefore, it's certainly a possibility.
CURWOOD: I want to ask you about a chart that you have. It shows that plants absorb a lot of carbon dioxide on the planet, and then abruptly, in about 50 years, they stop absorbing carbon dioxide from the atmosphere as a whole, and start putting it out. Can you explain why you make this prediction?
JENKINS: What we do is to look in the model at the vegetation, that same sort of effect that I was talking about previously of die-back in trees in the Amazon rainforest and so on. We then look at how much carbon is stored in that matter, not just in the Amazon but everywhere across the globe. And from that we can deduce how that varies from decade to decade, in the past and then in the future. And what we see is that at present, trees absorb carbon dioxide, so a good deal of the carbon dioxide that is emitted by human activities, transport and power stations and so on, will be absorbed into trees, will make them grow faster. And that will sequester, that will hold some of the carbon dioxide that otherwise would have gone into the atmosphere and raised carbon dioxide levels. Now, that's fine at the moment. What we do see from the model is that when this die-back occurs, some time in the middle of the next century, die-back of some of the forested areas of the world, then no longer will that be able to happen. So, the uptake of carbon dioxide will not occur, because the trees won't be there. And furthermore, when the trees die and decay, they will actually return carbon dioxide back into the atmosphere. So far from being a sink of carbon dioxide, they will become a source of carbon dioxide. And that has the potential to then put more carbon dioxide back into the atmosphere and exacerbate the problem in the first place. So it acts as a sort of positive feedback, if you like.
CURWOOD: And does your model then consider the effects of this positive feedback loop that gets set up?
JENKINS: No, it doesn't. What we don't have in the model at the moment, although we expect to have it in a year or so's time, is the interactivity that would allow that to happen, so we don't then put the carbon dioxide back into the atmosphere in the model. All we can do is to calculate how much there would be to go back in. What it turns out to be is something like 2 or 3 gigatons a year, that's 2 or 3 billion tons of carbon every year we would expect to return back to the atmosphere from dying vegetation. And that compares with the sort of emissions from human activities that we have at the moment, of something like 6 or 7 gigatons, 6 or 7 billion tons.
CURWOOD: Under the present international agreements, there are some substantial cuts that are called for in greenhouse gas emissions. But this plant die-back and feedback effect would wipe out what all the diplomats are talking about reducing human emissions by, wouldn't it?
JENKINS: That's right. If the sort of cutbacks are roughly the figure I was talking about, then unfortunately, whatever we do in terms of cutting back by that much will be compensated for, if that's the right word, by this die-back process in the sort of scenario we see.
CURWOOD: Thank you, sir.
JENKINS: You're very welcome. I enjoyed talking to you.
CURWOOD: Jeffrey Jenkins heads the British government's Hadley Center for Climate Prediction and Research.
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