How Dangerous Is Global Warming?

Last week, President George W. Bush again denounced the Kyoto global-warming agreement of 1997, insisting it would require unattainable reductions in greenhouse-gas emissions. Moreover, he dismissed a substantial body of science that strongly suggests both that global warming is dangerous and that it is being caused in large measure by fossil-fuel consumption and other human activity. While he called for more research on the issue, he insisted that, at this point, "no one can say with any certainty what constitutes a dangerous level of warming and therefore what level must be avoided."

A vast majority of scientists studying global warming insist that the phenomenon is real, that it is caused by man and that it presents potentially grave dangers. Several scientists, however, take exception. We invited one of them, Richard Lindzen, Alfred P. Sloane professor of meteorology at Massachusetts Institute of Technology, to have a dialogue by phone with Times editors and with a scientist more representative of mainstream opinion, Andrew Weaver, who holds the Canada Research Chair in atmospheric science at the University of Victoria in British Columbia.

Question: Professor Lindzen, nine years ago you said, "I can find no substantive basis for the [global] warming scenarios being popularly described. Is that still the case?

Lindzen: That depends. If you're talking about New York being underwater and palm trees in Washington, then the answer is still the same. There's no basis for that. Indeed, even if you accept warming as something that may occur and may be due to man's activities, statements that it will cause increased storminess and more intense hurricanes and so on still have no foundation at all.

Q: Professor Weaver, do you agree with that?

Weaver: Well, I do accept that warming has occurred, and I do accept that it will occur in the future. But to be fair, on both sides there have been alarmist points of views. I have a lovely picture showing the Statue of Liberty under water, which appeared on the front page of a tabloid. That's utter nonsense. On the other hand, you have the ostrichlike mentality of some who would argue that, in fact, not hing bad is going to happen and that maybe global warming is actually good for us.

Q: I'm curious where the points of agreement are. Do you both agree that, whether or not humans are the cause, the planetary temperature is rising in such a way as to slightly raise ocean levels in potentially dangerous ways?

Lindzen: I don't think there's solid agreement on that. You have to understand, the primary cause of sea level at any given location is a change in land level. Superimposed on this might be a small change due to thermal expansion of the ocean. That may very well continue because it has been going on for thousands of years. But it has been happening over millennia, and millennia don't have much to do with man. Sea levels have been rising since the end of the last glaciation. Over the last several hundred years, it seems that it has gone a little bit faster. I don't see much reason to suppose that this will change, and I do think that could have some implications. But what I'm saying is that climate is always changing, and we're always called on to adapt to the change. What I object to is the notion that there is something specifically different about today's change that you think you can identify with man. Normal change has been occurring and will always occur.

Weaver: What you haven't mentioned, Dick, is the rate of change. We know that sea levels have risen since the end of the last ice age by about 120 meters, and of course land rises and falls for natural reasons--because tectonic plates move and collide or because ice sheets melt. But the time scale associated with these changes is very slow. The rise in ocean levels we're seeing now is far too rapid to be solely associated with these natural occurrences. There is a lot of evidence that sea level will continue to rise. The oceans are warming, and warm water expands. It's also likely that glaciers will continue to melt. I do believe that this has implications for regions, like Bangladesh, that are affected by storm surges associated with tropical cyclones and the like. If you put a storm surge on top of increased sea level you have the potential for increased water damage.

Q: In your mind, Professor Weaver, what has caused this change in climate?

Weaver: Two things. First, there's natural variability in the climate system. There is seasonal variability, there is inter-annual variability. There are things like El Nino and La Nina. But there is no known natural climate mechanism to explain the warming over the 20th century. And that is one of the many pieces suggesting that a substantial portion of the warming of the 20th century is associated with greenhouse gases.

Lindzen: Some people argue that man can have no effect on climate, and I think that's nonsense. I agree with you, Andrew, on that. The argument is, will it be enough to worry about?

Q: What is the impact of humans?

Lindzen: Man is contributing to an increase in carbon dioxide in the atmosphere, and carbon dioxide is one of the greenhouse gases, albeit a minor one. The main greenhouse substances in the atmosphere, as the National Academy points out, are water vapor and clouds. In the models, water vapor and clouds act in such a way as to magnify what carbon dioxide alone would do by a factor of three or four. But there are highly uncertain aspects of the model. So we have a circumstance wherein the prediction that causes concern is based on parts of the model that are extremely dubious. Models have varying degrees of failure. They don't produce many phenomena that we know exist. It is a very profound assumption that the models can replace nature.

Weaver: I agree with Dick about the fundamental importance of clouds and water vapor. But these climate models are not as uncertain as he makes out. There has been great success in recent years comparing the paleo-record of climate with modeling results of the same period. We've found that, yes, indeed, the models do a very fine job of capturing global climate changes of the past.

Q: Professor Lindzen, to some degree you're a lone voice in the wilderness here. As we looked for people to represent the two sides on this issue, we didn't find many researchers embracing your point of view. Why do you think that is?

Lindzen: This notion of examining who's voting "yes" and who's voting "no" on climate issues is disguising the fact that there's broad agreement that some areas of the research are quite dubious.

Q: But aren't you standing somewhat alone on the issue of whether humans are a primary cause of global warming?

Lindzen: If you look at the United Nations' Intergovernmental Panel on Climate Change report, the actual report points out that we're in no position to make an attribution. Then, in the summary, it says that the group's opinion is that changes may be largely attributable to humans. I don't know what you do about that. You may wish to go ahead and believe that, but you should be aware that it's opinion. When you ask researchers what they really know , they tend to agree that it is not very much.

Weaver: I think we know a lot. I am not aware of a single study that can explain the warming that has occurred over the course of the 20th century without the incorporation of greenhouse gases as a factor. So that's one thing. We have a lot of studies that have detected warming. But I am not aware of a single one that can explain this without using greenhouse gases.

Q: And how does all this relate to policy? Should we be embracing the Kyoto Protocol?

Lindzen: Policy isn't so much our domain, but one thing that is very clear is that the Kyoto agreement would not change anything. It wouldn't change levels of CO2 in the atmosphere. It wouldn't reduce warming. So the notion that you propose the possibility of a problem and then proceed to take actions that have no relevance to the problem seems a bit weird.

Weaver: On Kyoto, I agree wholeheartedly, as would almost anyone in the scientific community, that it will have zero effect on global warming. However, for countries like Canada, the U.S. and Japan, meeting the standards proposed at Kyoto will be extraordinarily difficult. The only way to meet them is through changing technology. I support Kyoto not because it will have an immediate climatic effect, but because in order to meet it one needs to develop new technologies and change our conception of energy and how we get it.

Q: Kyoto aside for a moment, should we be trying to reduce carbon dioxide emissions? Do our concerns about global warming require action?

Lindzen: Some concerns have legitimacy, but we should prioritize our responses. You can't just say, "No matter what the cost, and no matter how little the benefit, we'll do this." If we truly believe in warming, then we've already decided we're going to adjust. So what's involved in adjusting? We know that the reason we adjust to things far better than Bangladesh is that we're richer. Wouldn't you think it makes sense to make sure we're as robust and wealthy as possible? And that the poor of the world are also as robust and wealthy as possible? Isn't that a better policy? I think what policy wonks like about Kyoto is that even if it does nothing about climate, it starts putting in place global monitoring and enforcement. Well, that's interesting, but how many people would want to sign on to an experiment in international policing of arbitrary regulations that have nothing to do with a specific problem? I think it's bad policy to tie changes and laws and regulations to problems they don't really address. If you say you are fighting global warming, and you adopt a policy that doesn't relate to it, then there's no way for the public to know if it's endorsed anything that works or not.

Weaver: As scientists, we love to observe change and try to understand it. But this is a dangerous experiment. We are moving into a new climate, and we don't know what it's going to be like. We know it will be warmer, and that the sea level will rise. We don't know, however, even if we were to stop all carbon dioxide emissions today, whether we've pushed the climate system past a certain threshold that would take us into an entirely new climate state, unlike anything in the last 400,000 years. And it's not us--it's our children--who will have to live with the consequences of our experiment.

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