Stephen Schneider

Global Warming: Science and Policy

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Professor Stephen Schneider
Professor of Biological Sciences, Stanford University
Senior Fellow, Stanford Institute for International Studies
Co-Director, Center for Environmental Science and Policy, Stanford University
MacArthur Genius Award 1992
Author, Climate Change Policy: A Survey
Website | Biography

While most atmospheric scientist now agree that the current trend in global warming is partly caused by the anthropogenic emission of carbon dioxide and other greenhouse gases, it is still unclear what effect this will eventually have on the global climate. Professor Stephen Schneider from Stanford University has been studying climage change for over thirty year and been responsible for bringing to the public’s attention the threat of global warming. He was awarded a MacArthur Fellowship in 1992 for his ability to encourage the discussion of global climate research through public lectures, media appearances, government testimony, and collaboration with colleagues.

Stephen Schneider (SS) joins Brian Gerke (BG) to talk about the science behind climate change.

BG: Dr. Schneider, thanks for being with us today.

SS: My pleasure.

BG: You have done a lot of work in the science and environmental policy realm. What is it like to inject science into a political debate on issues like climate change?

SS: Political debate has traditionally been based on this principle of balance where fraternalists quote the Democrats. They of course quote the Republicans. Absolutely appropriate doctrine for dealing with politics. The problem with science is rarely bipolar. Rarely do we have just one extreme or the other. And the problem I work on is climate change. Unfortunately, in the media you all too often in the articles see somebody from a ecology group telling you it’s going to be the end of the world or somebody from some oil company, enterprise, or institute telling you it’s good for you. Where is good for you and end of the world? The two lowest probability cases. The difficulty occurs when you apply a political model of reporting or advocacy models of getting information like getting courtrooms or in front of Congress to science because in science it’s multiple possibilities and they are not all equally likely, so what has to be understood by the public, in order to make choices and on rational policy, is the whole range of possible outcomes and how likely they are, not just the extremes that make a good pair for a battle in the op-ed wars. But that’s perspective, rather than balance of extreme opposites.

BG: Well, the goal is bringing the real science to the public.We will start out with talking a little bit about evidence and prediction. And so what is evidence for climate change and global warming?

SS: The key is to separate the parts of the science that we know very well from the parts we have some idea about from the parts that are speculative, that’s the perspective. The parts we know very well is that the world is about one degree Fahrenheit warmer than it was a century ago. The surface of the world. We know very well that there is 30% more carbon dioxide in the atmosphere. We know very well that’s the result of the Industrial Revolution and the agricultural revolution, clearing of land, deforestation, and mostly the burning of fossil fuels (coal, oil, gas). We know that there is 150% more methane in the air. That comes from animals, comes from land fills, from leaking natural gas, coal mines, and so forth. Now, why do we care about these gases: carbon dioxide and methane? Because they are heat trapping gases, that is the so-called greenhouse gases that warm the surface. We know that very well. Everything I’ve told you is not even remotely speculative. It’s completely well established. Period. The global warming is a fact in spite of what you may hear from the administration. Now, we got to move to the things we don’t know quite know so well. It’s a fact that the Earth is warmer, but is it a fact that this was due to us — that is the increase in carbon dioxide and methane — or could nature just have been perverse? Roll us snake-eyes and give us an improbable event. That we can’t be as sure of but we are getting pretty sure that at least a good part of that warming is due to us. And we do that, like in a good detective story by fingerprinting. You don’t just say well the world is warmer than it was century ago; therefore, we did it. I mean that is circumstantial evidence. You have to say what other evidence have you got? So we have evidence like the stratosphere, where the ozone is, is getting colder but surface is getting warmer. Some people, especially at Wall Street Journal, asserts over and over again, “Oh, this is a natural accident. The Sun got hot!” Well, of course, it’s ironic that the Sun decided to get hot in the last half of the 20th Century and didn’t for the last thousand years, but even if you bought the argument that the Sun got hotter, then it would have warmed up the stratosphere as well as the surface, but the stratosphere got colder. That’s a fingerprint of human effects of decreasing ozone and adding greenhouse gases when at the same time the surfaces warms. The second piece of circumstantial evidence saying that it is probably us. The other thing is our theory tells us that if we are adding this heat, then the high latitudes should warm up more than the low latitudes. That is because there is snow and ice there and it makes it more sensitive and it says that the Winter and Spring should warm up more than the Summer and the Fall. Both of those have happened. So now, we have four lines of fingerprinting evidence. Each one of which is circumstantial but together make such an overwhelming package that the vast majority of knowledgeable climate scientists have said that despite the remaining uncertainties, that it’s very likely (more than 90%), that humans are least part of the story. Finally, what is speculative is how much are we going to warm up by? One degree? Double what we are now? Or are we going to warm up by ten? That’s a difference between almost no impact and catastrophic impact. That’s more speculative because that involved predicting how many people will be in the world? What technologies will we use? Whether we have climate treaties signed or unsigned? Whether the uncertainty that still remain in the science work out on the mild or the unpleasant side? So there is plenty of uncertainty and speculation going around. But there is also a lot we know very, very well and what frustrates those of us in science is that stuff we know well gets mixed up with stuff that is speculative if it is all speculative, which it is not.

BG: For example these so-called fingerprints of human activities causing these things, each of them has an alternate explanation, but taken together they seem to really make the case?

SS: Yeah, that is exactly right Brian and you understood it well and I wish the average senator got it as quickly as you just did. The key here is that we are dealing in an analogy to a civil case with a vast preponderance of evidence. Now, in a civil case, a criminal case, beyond reasonable doubt. I don’t even know what that means. Is reasonable doubt 90%, 99%? That’s always interpreted by jury. But if we use a civil analogy where there is more than 50% evidence, they often award that person. We’re looking at two-thirds to 90% chance that each one of these circumstantial cases. You put them all together and you’re looking at a 95% case. This is so far over the top for a circumstantial case. I mean we buy insurance for health and car and fire when the probabilities that we are going to need it is 1%. So we are talking about better than coins flip odds. At the substantial change occurring at the scale of the planet, we need insurance at the scale of the planet. And people cooperating and acting together, not just acting in their self-interest by dumping all their waste into the atmosphere for free, but we need tailpipe charge for our dump and that will provide incentives for people to dump less. What that means is that the people who have been doing it over these years are going to have higher costs and they know it. They organized and happen to have the president’s and the vice-president’s ears because both of them are former oil company executives.

BG: Okay, so we’ve talked about the past and evidence. Let’s talk a little bit now about trying to predict the future. I think even for those who accept the evidence so far and believe and perhaps know a little bit of science, it may be a little frustrating to see all these models widely diverging in their predictions. One might ask the question, “If one can’t even predict the weather well, then how are we going to know what’s going to happen with this stuff?” Can you talk a little bit about that?

SS: That question is asked all the time, “Oh, aren’t you guys a joke! You know, you can’t predict the weather accurately after a week or two, so how dare you talk about 10 years from now or a hundred years from now.” I always like to have a bet with these guys. Okay, I’ll bet the long-range forecast. I’ll bet that January of 2005 is going to be 15 degrees Celsius colder in the Northern Hemisphere than July of 2005. You know people start laughing and they’re like, “I’d be dumb to take that bet.” That’s exactly, it’s long range forecast. How is it we can do that one accurately but we can’t accurately forecast if the weather next week is good because they are completely different problems. The weather is what scientists call initial value problem. You start out with initial knowledge of where all the storm systems are and you let them evolve forward in time and after about 10 days, you lose all skill. Whereas the climate is what we call a boundary value problem. That is you change things at the boundary of the Earth like the amount of Sun coming in between January and July or in the case of global warming, the boundary conditions that you are changing are the amount of greenhouse gases which changes the amount of heat trapped and then you are predicting averages. You are not predicting the instantaneous day to the atmosphere. And there is no prohibition against doing that. In fact, we know how to do it. The problem is how well do we know how to do it and that’s where the difficulty comes along. In principle, there’s no reason why we can’t make long range climate projections. In practice, there are complicating factors that make it possible to have a crystal ball into the future but the crystal ball is partly cloudy, not clear. In fact clouds are the whole key. To heat the Earth up, we are going to evaporate more water. That everybody agrees. If you put a pan of water out in the Sun as opposed to the shade, you know it’s going to evaporate faster. So that means, when the Earth is being heated by the extra greenhouse gases and we’re virtually certain it’s going to evaporate more water. Well, when that water condenses into clouds, the clouds are bright and white and they reflect away sunlight. And if they are reflecting away sunlight, they will cool the Earth back down. We even have a name for this. It’s called the negative or stabilizing feedback. So, of course those people who think the problem will be minor point to that possibility, but what they forget is if you increase the evaporation, you not only make the clouds wider, you might make them taller. If they are taller, the tops go higher. Anything higher in the atmosphere is colder. Anything colder gives off less heat. Therefore, they are actually trapping more heat and they are amplifying (calling it positive feedback). What we are frustrated about in atmosphere science is that we can not pin down to more than a factor of three. How these clouds, what we call cloud feedback, is going to influence our projections for the future. So therefore you can still defend mild and catastrophic outcomes for the future as possible. Even though they may not be the highest probability case, they can still be done responsibly. You can say it could be really catastrophic or really mild, and guess what the coal industry takes? The really mild and pretend it is the truth. And Greenpeace takes the other end and pretends it’s the only case. People are confused with this political reporting model of one extreme against another.

BG: So to bring some sanity to this, can you tell us since you are an expert, what are the extremes and the probability of the extremes? And then what is perhaps the more highly likely outcome that we might see?

SS: Well, if we are very lucky, what happens is that we don’t warm up temperatures more than a couple degrees. That gives us longer growing seasons in the higher latitudes. We are adding carbon dioxide (CO2) into the atmosphere, which is a fertilizer for crops and trees, so we end up with higher crop yields and longer growing seasons. And the climate change won’t be very large, but we will have extra CO2. On balance we may be fine. Now, of course what that forgets is the other side of your question, which is what about the downside? If you are already living in the tropics, it’s already sufficiently hot. The extra heat usually reduces your capacity to grow crops, so we have the ironic situation that even at the lucky end, the rich countries in the North who might do fine for small climate change, the poor countries in the South probably will be hurt. So if the rich gained one percent of their economy, the poor lost. You know, the rich got richer and the poor got poorer. Even that is not a prescription for a happy world. So, even the happy case has hooks in it. Now what happens when it warms up 5 or 10 degrees, which again I would assign a 10% chance. It would go that high just as I decided 10% chance that we could be as lucky as 1 or 2 degrees more warming. In that case, you’ll be taking the species of the world, which now live in habitats that are increasing being fragmented, just by humans cutting down forests and transforming prairies to agriculture and so forth, and not only are we squeezing them into smaller and smaller spots, but now we forcing them by climate change to have to move hundreds if not thousands of miles. And, they would have to move across disturbed landscapes like factories, farms, and urban settlements. The probability that currently endangered life would go extinct would be very high and that many, many currently okay species would become endangered would be high. So I think we would be looking at a pretty serious threat to nature if we had that kind of change. If we have 5 to 10 degrees warming, we are going to raise sea levels quite a bit. A foot or two in this century at least and probably many, many yards over the next 500 years. That will make coastal areas substantially in trouble and small island states would eventually disappear. It will probably increase in the intensity of hurricanes, droughts, and floods. That’s a pretty nasty set of prospects that we would face. In the tropics, where it is already hot, adding another 5 degrees would be quite catastrophic in a variety of ways including just the direct heat stress on people and areas that are already a bit tolerant to plants and animals. What we keep saying in the climate impact business, can we keep this under a few degrees? Can we keep carbon dioxide from doubling? Can we please begin to replace the inefficient Victorian technologies to get rich with new high technology, low-impacting technologies so that we can improve our odds of being on the low side of impacts rather than the high side? That’s basically how the community tends to react.

BG: Looks like we are just about out of time. I just want to thank you for a fascinating look into the science behind this political debate.

SS: Well, thanks for asking and I appreciate the opportunity to let people know that they better listen to the claims they hear and make sure that they are not just hearing somebody tell them that this is truth of what will happen. Trust the people who are talking in subjective probabilities and ranges much more than the ones who have mistreated truth-telling.

BG: Thank you for joining us today.

SS: Thank you.


  1. […] Dyson’s general attacks on computer modeling studies of climate change exclude the “preponderance of  evidence,” physical evidence, that suggest big changes are […]

  2. […] facts.”  Dyson’s general attacks on computer modeling studies of climate change exclude the “preponderance of evidence,” physical evidence, that suggest big changes are […]

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