U.N. Prepares to Release Report on Climate Change

Friday morning, the United Nations Intergovernmental Panel on Climate Change will release its fourth assessment about the science of climate change. The consensus statement will serve as the most authoritative benchmark on this sometimes contentious issue.

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From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block.

ROBERT SIEGEL, host:

And I'm Robert Siegel.

Two hundred scientists and government representatives from around the world have been meeting in Paris all week. Their task, hammer out a new consensus statement about global climate change. Their report is part of a process that's designed to help nations shape their responses to a warming globe. And it's being watched very carefully because it will be the most definitive word on climate change this decade.

NPR's Richard Harris reports.

RICHARD HARRIS: There should be no big surprises in the report since it is supposed to reflect the published and widely accepted studies about climate change. That means it won't look a lot different from the last intergovernmental panel on climate changes report, which was issued in 2001. That said, scientists are more certain now than they were that human activities are a major cause of recent climate change.

But Robert Lempert, a scientist at the Rand Corporation, says that somewhat higher degree of certainty really isn't that meaningful.

Dr. ROBERT LEMPERT (Rand Corporation): If you are trying to manage risks that clearly, it doesn't matter all that much whether your 90 percent sure or 50 percent sure, you're going to be taking steps to try to address that risk.

HARRIS: But what it does do, he says, is feed into the public consciousness about climate change. And that has shifted a lot since the last report came out in 2001.

Dr. LEMPERT: There is a real psychological tipping point where people most universally acknowledge that yes, this is a problem we need to deal with. And I think once you get pass that point, then it opens up a new debate.

NAYLOR: So another way of looking it, that would be, this is by and large the same message we got in 2001, but people are looking at it in a fresh way?

Dr. LEMPERT: I think the audience has definitely changed, as people feel things going on in their lives, in their backyard, and they're going to pay attention to this in a way that they hadn't before.

NAYLOR: And Ralph Cicerone, who heads the National Academy of Sciences, says even though there hasn't been a dramatic change in conclusions from six years ago, there has been a lot of progress in the world of climate science.

Dr. RALPH CICERONE (National Academy of Sciences): The last six years had been notable in that the data becomes so much more clear than people expected. Also, a couple of theories that people had in mind about why climate might change under other forces, or discrepancies in the record have been removed with these last six years.

NAYLOR: That means among other things that scientists have been able to refine their forecasts. Some of the worst case scenarios and some of the best case scenarios now appear less likely. The central estimate should remain about the same, which means, for example, global temperatures are most likely to rise five or six degrees Fahrenheit in the coming century, plus or minus a couple of degrees. Of course, that assumes that forecast of future emissions of greenhouse gases are accurate. Cicerone says that's even harder to predict than the climate.

Dr. CICERONE: Of course, that's another way of saying that humans are right in the middle of the situation.

NAYLOR: Now it's worth saying a word or two about how the scientists arrive at their conclusions. The final discussions in Paris end up with somewhat of a conserve statement, because they involve both scientists and government representatives. Before leaving for this week's final meeting, co-chair Susan Solomon said even so, the government officials don't distort the result.

Dr. SUSAN SOLOMON (National Oceanic and Atmospheric Administration): The experts push each other back just as hard as the governments push the experts back, or push them forward at various times.

NAYLOR: One difference with this report, which is the fourth consensus statement on climate change, is that the organizers reached out to attract scientists with fresh perspectives.

Dr. SOLOMON: Seventy-five percent of the authors of this report did not work on the third assessment, so they are giving us a fresh look. And about a third of them when they were chosen had their highest degrees for less than 10 years. So that was our definition of what was young.

NAYLOR: One shortcoming of this process is that it's not too hard to come up with projections of continued and gradual changes in the planet. But Robert Lempert at RAND says the real concern about climate change is that it can hold surprises. And those are difficult, if not impossible, to predict. Even so, he says the consensus seeking report is important.

Dr. LEMPERT: To deal with highly uncertain problems, it's useful to know what you know. And it's useful to have some sense of the boundaries of your knowledge and to know that there are potentially surprises lurking out there, is useful as well.

NAYLOR: Now, this scientific assessment is just the first of three reports in the IPCC process. Later this spring, scientists and government officials will issue one report that will update expected impacts of climate change. And another that will discuss what we can do to mitigate the effects.

Richard Harris, NPR News.

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