RAY SUAREZ: And, for that, I am joined by a member of the IPCC panel, Michael Oppenheimer. He's a professor of geosciences and international affairs at Princeton University.
Professor, welcome to the program.
MICHAEL OPPENHEIMER, Princeton University: Glad to be here, Ray.
RAY SUAREZ: What is the major difference, the major refinement in this latest report from the one that precedes it?
MICHAEL OPPENHEIMER: There are three new high-level messages.
One, it's now stated as extremely likely that most of the warming of the past 60 years is due to human activity, and that's very unusual for scientists with a complex problem like this to state something with such a high level of certainty.
Secondly, the projections of sea level rise in particular are about 50 percent higher than in the last report. That's because we have a better grip on what the big ice sheets in Greenland and Antarctica are going to do. And that's a very troubling development, because, as we saw in Hurricane Sandy and other coastal storms, the combination of intense storms with an unusually high sea level causes an extra level, a tremendous level of flooding inland and is very destructive.
And the third message is that the window of opportunity to avoid a dangerous warming, which has been labeled by the governments as a warming of a little short of four degrees Fahrenheit, that window is closing rapidly.
And we could, by short of the middle of this century, say, some time between 2040 and 2050, emit so much of these gases, if we don't change our course, that this dangerous warming, where the risks just pile up and adaptation becomes very difficult, and in some cases impossible, that that kind of warming will be inevitable.
RAY SUAREZ: When you move in the space of one report from calling something very likely to extremely likely, these are terms that people use regularly in their daily lives, but do they have, when you say them and people like you say them, something more like scientific precision? It is more than nuance to go from very likely to extremely likely?
MICHAEL OPPENHEIMER: These terms are used with great precision.
They're defined very carefully in the report, so that very likely means better than a 90 percent chance, and extremely likely means better than a 95 percent chance. And so this isn't casual language. This means the scientists looked at the problem carefully and decided that the case is ironclad. And that's all up and down this issue.
There's a big central focus on this issue on many facts, that the Earth is warming, that the warming will continue, that the dangerous warming is coming close, and that if we don't do something about emissions, we will be there pretty soon.
All of that is now known with a -- there's a consensus about all of that. Scientists are very careful. Scientists tend to be skeptical, of course, and here we have thousands of them getting together and being able to agree on this high level of certainty.
There is no environmental problem that is characterized by that level of certainty.
RAY SUAREZ: You're constantly getting new data in from around the planet. Have you got any new information that caused the IPCC as a body to back off from earlier predictions of effects down the road, or is everything being reinforced, that -- the predictions that were made in earlier reports?
MICHAEL OPPENHEIMER: No, there are certain things that we think we're a little less certain about or that -- where we have lowered the projection.
For instance, the climate sensitivity, as it's called, the response of the atmosphere when CO2 doubles, it had a range in the last report of about three -- two to 4.5 degrees Celsius -- in Fahrenheit, you can about double those numbers. That -- the bottom limit on that range has been dropped a little bit. So it's conceivable, with a doubling, instead of a warming of two degrees Celsius, we will have 1.5 degrees, which is about three degrees Fahrenheit.
But, on the other hand, in the report previously, previous to the last one, the number that was used was the same as it is now. So that shows you the scientists are forever fine-tuning and trying to incorporate new knowledge. Scientists are obsessed with getting the answer right, with staying up to date. And if the answers lead us in a direction of thinking we're less certain or the effects aren't going to be quite as bad, we going to say that, too.
RAY SUAREZ: Some scientists and academics cast a more skeptical eye on the work of the IPCC. Among them is Roger Pielke, who is a professor of environmental studies at the University of Colorado.
And looking over the latest report, he says: "The IPCC's dismissal of the significance of the recent hiatus in global temperatures is sure to be seen by its critics as a dodge. The IPCC would have been better served by taking on this issue more directly."
And on the topic of carbon emissions: "Progress on that front will have to come in the context of some well-established certainties, many more fundamental uncertainties and a good bit of ignorance about what we don't yet know."
What's your response?
MICHAEL OPPENHEIMER: Well, Roger is completely wrong about the so-called hiatus. That is, the scientists looked at it very carefully. There's an extensive discussion of it in the detailed background documents will be made public on Monday.
RAY SUAREZ: But hadn't there been a pause in the rise in surface land temperatures?
MICHAEL OPPENHEIMER: There's been a slowdown. It hasn't stopped. The warming rate has been slower over the last 15 years than the long-term trend.
And that is believed to be because the climate is quite variable. If you look at the long-term record, there are bumps upwards, there are bumps downwards, and there are plateaus like this one. After every bump downward or every plateau, the climate change then accelerates again. Now, we can't be sure that is going to happen, but it's a good bet.
The best possible -- the best -- the leading explanation of this is that heat tends to hide in the ocean sometimes. But when heat hides in the ocean, it later comes out and reappears in the atmosphere, and then warming resumes faster than before. We don't know this for certain. We will find out over the next few years.
But it's wrong to say that the IPCC didn't look at it carefully. It certainly did.
RAY SUAREZ: What about sea ice? Recently, critics have made much of the fact that there was a measured increase in the amount of sea ice from year to year in the past few years.
MICHAEL OPPENHEIMER: There's no question at all that the long-term trend for Arctic sea ice is down, down, down.
But just like with the temperature trend, it's variable. The wind circulation patterns, ocean circulation patterns will change the amount of ice in any given year. So you see bumps in the record. There was an extreme bump in the downward direction the year before, and now this year, the amount of sea ice has increased. And over the long term, those bumps average out, but what they average out to is not zero.
They average out to a long-term downward trend, which is expected to make the Arctic ice-free in summer by the later part of this century. And that is a startling trend. All in the course of a few decades, we're losing the Arctic ice pack.
RAY SUAREZ: Michael Oppenheimer is one of the scientists who contributes to the reports of the IPCC.
Professor, thanks for joining us.
MICHAEL OPPENHEIMER: Thanks for having me here.