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Global Warming Conference: The State of Climate Change Science
Global Warming Conference: The State of Climate Change Science
July 15, 1997
MR. ADLER: All right. We are getting ready to start back up again. If you folks could please take your seats.
Good morning. My name is Jonathan Adler. I direct the Environmental Program here at CEI. And as both Senator Craig mentioned and Fred Smith mentioned, there is a lot of discussion about the planet. And we are going to be hearing a little bit more about that this afternoon. But we also thought it would be useful at the beginning of the day to try and give everybody an idea of where the science is and where it isn't in terms of climate change.
One of the reasons for doing this is I think that even folks who have spent a lot of time dealing with these issues and dealing with environmental issues can sometimes be confused about what the science does or does not say. New studies are published all the time. We see the headlines. Sometimes the headlines conflict. Sometimes the experts conflict. Those of you who were at the hearing last week, the Senate Environmental and Public Works Committee, heard Dr. Steven Schneider and heard Dr. Richard Lindzen giving very different views about what the levels of uncertainty are and what the science is and is not showing. We'll also hear some different perspectives later this afternoon.
President Clinton, on June 26 made a remark that the science is clear and compelling, we humans are changing the global climate. And that is something that we certainly hear a lot. But then we also saw an article on Science Magazine in May of this year where some of the lead authors in the IPCC report said that the human attribution is not a done deal in terms of the climate. And the former Chairman of the IPCC recently remarked in Europe in a debate with Dr. Fred Singer of the Science and Environmental Policy Project, who I know is here today, that there has been no effect on countries from any current change and that we are not seeing the effects yet. So I think it's understandable that a lot of people aren't sure. Well, what does the science show? What doesn't it show? Do the land temperature records matter? Or do the satellites matter? And to help us pull some of this together and someone who is on the same page at least for this morning, we have asked Dr. Roy Spencer to give his views of where the science is and where it isn't with regard to climate change. Dr. Spencer is Senior Scientist for Climate Studies at NASA's Marshal Space Flight Center in Huntsville, Alabama. He directs research into his development and application of satellite passive microwave remote sensing techniques for measuring global temperature, water vapor and precipitation. Dr. Spencer is a recipient of the American Meteorological Society's 1996 Special Award for his satellite-based temperature monitoring work. And he received NASA's Exceptional Scientific Achievement medal. Dr. Spencer.
DR. ROY SPENCER: Thank you, Jonathan. As Jonathan mentioned, I'm here to give you my perspective of what we do and don't know about global warming. I'll also give you an update on global temperatures based on our satellite data. That's something that we update every month.
But first of all, I want to point out that even though I'm a NASA researcher, I am giving you my opinion as a scientist and what I say shouldn't be construed to be any kind official position of NASA. NASA funds both government and nongovernment researchers. These researchers come to different conclusions based on what kind of research they do.
And as Jonathan was alluding to, researchers do sometimes disagree. And that's confusing sometimes for the public because scientists are just to supposed to work with the facts, right. We just deal with facts. Unfortunately, it's the interpretation of those facts that we tend to disagree on. And I thought it might be useful to point out that in areas of science that are controversial that there are other things which influence a scientist's judgment. And I listed some of them that I have personally seen from other scientists including myself -- okay, I'm not saying I'm immune to these influences.
Search for truth: I figured I'd better put that at the top as the biggest motivation. You know, scientists want to understand how things work and hopefully put some of that understanding to good practical use. But also I've seen that scientists are motivated to a greater or lesser extent by the quest for research funding. Certainly global warming is a good area for submitting proposals to get government funding to do government-funded research. And I agree that the threat of global warming is sufficient to where we should have that funded activity.
Science community peer pressure -- I'm going to show what I think is an example of that later in my talk -- other scientists are right assumption. Now that takes some explanation. What I mean there is that there are very few climate scientists that have enough knowledge of the big picture of how weather systems work in the context of the global climate system to give a qualified estimate of how much global warming there is going to be. The people that do make pronouncements on how much global warming there is going to be are usually the scientists that are more in the public eye. And they have other motivations than just the science. So usually what you have is that the scientists as a group will sort of sign up to what the experts say and support their own, you know, their own group of scientists that even though individual climate scientists might only work on one little piece of the problem -- and that's usually what happens -- they still say, you know, but we'll agree that there is global warming and that it is a big threat because other people that work that problem know that that's the case.
I've seen the desire to save the earth. I mean, obviously, that's a commendable desire. And that's sort of related to this last point that I've got on the list. Let's jump down there, world view. This is maybe the most important thing which influences a scientist's perception. People that traditionally work the climate change issue aren't meteorologists. Meteorologists deal more with daily weather, and they have a feeling for what weather systems do and why they do it. If you go back about 30 years, the original climate scientists were more experts in radiation or physicists who didn't know that much about weather. And those first researchers ended up overestimating the amount of global warming there would be in response to increasing levels of greenhouse gases. That's because they didn't understand the ways in which the atmosphere responds to a forcing.
Okay, there's certainly a desire to develop your own pet theories. And once you have one, you're reluctant to let go of it.
And then some scientists are motivated by the interest from the media.
Now this isn't meant to be an indictment of the scientific process. I just want to point out that scientists are people too. And while the most objective people I've ever met are scientists, for the most part, people that speak out on the issue of global warming have greater motivations than just searching for how things work.
Okay. I thought I'd give you the IPCC's estimate. As most of you probably know, this is the UN-sponsored, intergovernmental panel on climate change, the official, international word on what the future of global warming is. And their first official report came out in 1990. I'm a member of this group, this 2,500 scientists that are involved in the IPCC process.
In the 1990 report, it was estimated that future global warming, at least until the end of the next century, would run about three-tenths of a °C per decade. In 1992, they came out with an interim report and basically said there was really no new science that would substantially change the 1990 estimate of three-tenths of a degree warming although they hinted that we're learning more about aerosols and that aerosols might indeed reduce the amount of warming. Now we've just had the latest report come out, 1995 report, which was released in '96. And the estimate of global warming has been reduced to about .18 degrees per decade which comes from an estimate of 2 ° warming, 2 °C warming by the end of the next century. The next major report is probably going to be 2000. I imagine it will be 2001 before it's published, at which time we'll have a new estimate.
But you can see that there is a trend downward. And I think there's a good reason for that. I'm going to talk about that a little bit. First, though, let me give you the satellite temperature update. We use the NOAA satellite, those microwave sounding units which were built by JPL and have flown on the NOAA weather monitoring satellite since 1979. And we've merged eight of these satellites together, inter calibrated them, to come up with a global temperature record since January 1979. So it's now 18-and-a-half years of satellite data we have. And this shows the update through June of this year. It shows that we are still a little below normal out of the 18-year period. And you can also see that there is a lot of year-to-year variation in global temperatures. That's related mostly to El Nino and La Nina which are sort of a climate fluctuation, the biggest climate fluctuation that we know of on earth that happens rather routinely every few years, and also due to volcanoes. This was the first really clear signal of volcanic cooling due to a volcano, the Pinatubo eruption from 1991 caused the northern hemisphere in the summer of 1992 to be quite a bit cooler than is normal. The Pinatubo eruption is estimated to have reduced sunlight by as much as two to four percent.
In contrast, a doubling of CO2, which is supposed to occur late in the next century, has a radiative forcing about one percent of normal. Now there are different kinds of radiant forcings. This was turning the sun off. This cooling effect due to Pinotuba was basically shading the sunlight. Increasing concentrations of CO2 don't affect that. They affect the other radiation which is the earth's cooling radiation, the infrared radiation that escapes out to space and balances all of the incoming solar. Now climate models tend to react the same way with whichever kind of forcing is used. They can turn up the sun by a percent. And they can turn up the trapping of infrared radiation by a percent. And the model acts the same. But I personally -- and some other scientists don't believe that -- because the way solar energy and infrared energy are transferred in the atmosphere are very, very different.
Now the trend of our satellite data -- this is just a different plot of our satellite data with some other data sets. I neglect to mention that our satellite measurements are for a very deep layer. It's from about the surface to an altitude of about six kilometers. So we call them troposphere temperatures. For that 18-year period, our satellite temperature trend is a cooling of four-tenths of a degree per decade. No doubt that wouldn't have been a negative trend if it weren't for the Pinotuba eruption. And the IPCC, for the most part, doesn't include -- was there a comment?
MR.: (Off mike.)
DR. SPENCER: I'm sorry four-hundredths of a degree C per decade. And probably this cooling from Pinatubo is a large portion of that cooling signal. It probably wouldn't have happened otherwise. Now I also put on here, the surface temperature measurements from thermometers. There are a few groups in the world that are doing monitoring of global temperatures with thermometers. Obviously, the temperature data over the ocean isn't very good. And there's different data sets. Here's climate prediction center for the land -- they have an upward trend since 1979 of fourteen-hundredths per decade. The IPCC, which is sort of the international official temperature trend, its data set is plus .13 °C per decade. And then Jim Hansen at GIS has folded in NOAA’s sea service temperatures data with his data. He gets about nine-hundredths warming per decade.
Now, these days, there is getting to a lot made of the difference between the satellite, deep-layer measurements, and the surface thermometer measurements. Note that the surface thermometer measurements, point one-three is starting to approach the predicted warming of point one-eight degrees C per decade. The deep-layer doesn’t show that warming. We are still trying to understand why - we don’t yet understand why this is the case.
One paper has been published in Nature, which has been critical of our satellite intercalibration. But, Nature has just accepted for publication, our rebuttal to that article which had several serious factual errors in it. I do want to point out that the satellite measurements do have independent validation, which the surface measurements don’t. The other way you can measure deep-layer temperatures is with weather balloons and there is two other weather balloon datasets for global temperatures. One from the UK Met office; Jim Angle from NOAA - and you can see that they agree with the satellite temperature trend. So why there should be a difference in trend in the deep troposphere versus the surface, we don’t know – its something that the global climate models, GCMs don’t produce and we are still trying to understand that, but I suspect it has something to do with water. And I will get back to that in a minute.
As I mentioned, our satellite temperatures are validated with radioson data, they’re independent of the radioson data, this just shows our own calculations of monthly global temperature anomalies from the satellite from ’79 through ’94. Based from 97 radioson locations in the Northern Hemisphere and you can see they track each other very nicely. And the temperature trend in our dataset, in our radioson dataset -its about 200ths of a degree warmer in its trend than the MSU. That is the area that the satellite does see warming - its Northern Hemisphere, mid-latitudes. Where the land is. Where the people live. We do see warming in the last eighteen years for that area.
Now, there are a few areas I want to highlight as being uncertainties in global warming theory. The first one is one that most GCM modelers think is solved - called water vapor feedback. The increasing greenhouse gases in the atmosphere, as I mentioned, trap more of the earth’s cooling infrared radiation and don’t let it escape the space and the theory says that the earth is supposed to heat up until it regains a balance between the incoming solar radiation and the outgoing infrared radiation. If that were to act by itself, you would expect a one degree warming due to a doubling of CO2 sometime late in the next century. What’s really uncertain though – I mean, that has some uncertainty associated with it – but what is really uncertain is the feedbacks. What feedbacks are are the climate system’s response to this initial forcing. That CO2 should be trapping additional infrared energy. But then how does the climate system respond? How will water vapor change? If water vapor changes to enhance the warming, that is a positive feedback. If the water vapor changes to mitigate the warming, that is a negative feedback. Same way with clouds. If clouds were to increase by a few percent, lets say it could entirely through a negative feedback, cancel the CO2. There still would have been a change in the climate system, but the net effect on temperatures would be to cancel it. But most GCMs actually decrease the cloudiness which causes more sunlight to come in - which is a positive feedback.
So that is what most people are working on are these feedbacks. What are the feedbacks due to the CO2 forcing? Well the water vapor feedback is basically supposed to about double that warming due to CO2. Its a positive feedback in the GCMs. And there is a number of us that think that that doesn’t exist. That that has not been demonstrated to exist. Its interesting. This is an area where a number of scientific papers have been published in different scientific journals which are flat out wrong. There aren’t many things that I am sure about in my life, but this is one thing that I am sure about. That what they did had nothing to do with water vapor feedback. And in fact, we just published a paper in the bulletin of the AMS, which just appeared a couple of weeks ago, which shows that the GCMs don’t have the physics in them to produce water vapor, changes in water vapor, that would be associated with water vapor feedback. The physics just don’t occur in the models. So, I view this as still a major uncertainty. It was almost swept under the rug totally in the 1995 IPCC report; because the modelers think they understand this. And the reason they think they understand it is because when they run their models, all the models get about the same water vapor feedback and they figure they can’t all be wrong - so they must all be right.
Plus there are these other studies which purported to validate positive water feedback, but which don’t. Now what the modelers are more interested in is the cloud feedback and how clouds respond. And I’ve got some results to show you from that. These are the two main things I want to talk about, is water vapor feedback and cloud feedback and then aerosols is getting interesting. You probably had heard that the excuse for the reason why we haven’t seen as much global warming as we should have by now has been that the man-produced aerosols are reflecting sunlight. But now, it is being better understood that, apparently, aerosols don’t have as much cooling effect as we had thought and indeed might absorb an awful lot of sunlight. And may not have as much cooling effect on the climate as we thought and if we can’t blame it on aerosols, maybe we need to go back to water vapor feedback as the culprit.
Now, I made up this cartoon to describe how the atmosphere operates. If there is one thing that the atmosphere does best, OK - I am going back to fundamental law. And that is the second law of thermodynamics. The atmosphere is always readjusting itself to get rid of excess heat. OK? Now, before I forget, I want to mention something about the earth’s nature greenhouse effect. You’ve all probably heard that the earth’s natural greenhouse effect is our friend, because it makes the earth habitable - it keeps the earth warm enough. What isn’t pointed out, usually, is that if the earth’s greenhouse effect were allowed to operate by itself, the average service temperature on the earth would be about 112 °F. Much higher in the tropics. OK? Seventy five percent of that greenhouse effect induced warming at the surface is never realized. The reason it is not realized, is because the atmosphere sets up circulation to take that heat away from the surface, usually in the form of evaporation - evaporation of water you know that cools your skin, it does the same thing to the earth. This water that is evaporated into the air follows the air currents, which themselves, are driven by imbalances in temperature between one location and another. Which feeds rainfall systems. These rainfall systems then take all that heat that has been accumulated at the surface and release it, when that cloud is formed, that heat is released. Up higher in the atmosphere, like a chimney. That heat, because warm air raises, that heat pushes the air higher and higher; sucks more warm moist air in from the bottom and produces more rainfall. But for all of this rising motion in the atmosphere there has to be the exact same amount of compensating sinking motion elsewhere - that’s what these arrows represent.
This is where most of the earth’s infrared radiation is being lost. It is from clear air, in between the clouds, that is sinking. Its the humidity of this layer that is most important to global warming theory. OK? The humidity of this layer. Where does this layer get its humidity? It gets it from these rainfall systems. If you watch the next thunderstorm that you see, the top of the thunderstorm spreads out; that anvil material spreads out in the clouds. The clouds spread out in the upper troposphere out to the side and then disappear. That’s because they are re-evaporating - that’s what moistens the troposphere. It is the detrain cloud material from these rain systems that then moistens this layer. This layer and how moist it is … the moisture mostly controls how much infrared radiation is lost to space.
We have new satellite measurements of the humidity of this layer - of the middle and upper troposphere. I don’t now if you can see it?. Here is North America, here’s South America. This is one day’s worth of measurements - these black areas is where the satellite didn’t see on that particular day. This is the humidity level of the middle troposphere. And all these white areas are areas where the relative humidity is below about ten percent. These are the radiative exhaust ports of the atmosphere - of the earth. These are the radiative exhaust ports - this is where most of the radiation is lost or the greatest portion of the radiation is lost. Now, I mentioned that it is the detrained cloud material from these rain systems that moistens this layer. The physics, which control that moistening, we call it precip efficiency isn’t even contained in the GCMs. Oh it is implicitly, but people don’t talk about it, we don’t check it, we don’t even understand what controls precipitation efficiency. But they have something in the GCM’s that causes rainfall and causes the cloud to re-evaporate, but we really don’t know how that process changes during a warming period or a cooling period. So, the point of our paper was that we really don’t know yet whether there is positive water vapor feedback and as I mentioned, that basically doubles the influence of that initial warming due to CO2.
I think the last thing I want to show here, is the effect of cloud feedback. This shows two plots, one is for 1990 - the first IPPC report, the second on is from ’95 IPCC report. This shows cloud feedback in 19 different climate models. Each bar is a different climate modeling group. Back in 1990, this shows how those 19 different models were handling clouds. It shows that there was a great deal of warming evident in a lot of these models back in 1990. In ’95 we see the average level of warming, due to clouds, which is a positive feedback - in these models, anyway - has been greatly reduced. Back then out of 19 models, there were only four that actually had a negative cloud feedback. In 1995 we are down to 18 models in this graph and there a total of eight models that have a negative feedback. Now, my view is, we know so little about cloud feedback and water vapor feedback, which are probably the most important feedbacks to CO2; that for me at least, I think the safest thing to assume is that the earth will continue to do what it does best - that is reject excess heat. And if I were forced to make a prediction, I would say zero feedbacks. I think the net feedbacks, due to water, in the form of clouds and water vapor is going to be negative. But for right now , I could probably be convinced that maybe - yeah, we’ll just see direct radiative effect of CO2 which maybe, might give you, one - one and a half degree C by the end of the next century. But, I don’t have a whole lot of confidence in that. But I have even less confidence in positive feedbacks in the climate models. And I think as the new reports come out, say in the year 2000, that these estimates of global warming will be further revised downward.
MR. ADLER: We have about five minutes for questions. I would ask people if they can to use the mike.
Q: You said you were going to tell us why the IPCC estimates of warming have been revised downwards. But I guess you didn’t have time to. You showed the graph that they have changed since 1990, but you didn’t mention why. And, I just wanted to… I was just looking at the IPCC report and it says clearly that there is two main reasons: one, is that models now consider aerosols , before they didn’t. So if you tell the model that there will be less sunlight, then of course it produces more cooling and aerosols weren’t understood well enough in 1990 to include in that report - so that is one reason that the results are lower. The other reason is that they have chosen a different scenario for future CO2 emissions, so with less CO2 it will not be as warm. Isn’t’ that why the estimates are lower now?
DR. SPENCER: Well, I think that this has got to contribute to it. Although I couldn’t find where they explicitly mention this. That the cloud forcing has gone way down. I don’t know why they didn’t mention that, because the graph indicates it. This value here of one on this scale is where the cloud forcing equals the CO2 radiant forcing so if basically doubles the effect. And clearly the average cloud forcing has gone way down, although they don’t mention that in the summary.
Your right, I should have mentioned those elements that there are different reasons for the estimates coming down. But also, you got to point out that the people that read these reports, including the policy makers summary, what they are looking for is; how much warming do you expect in the next 100 years? How much per decade? And that has been revised downward. But you are right, part of the reason is they are assuming lesser CO2 emissions as well. So there is a combination of reasons. They still have full fledged positive water feedback though and I think that that’s the next thing that needs to come down.
Q: Dr. S. Fred Singer: Perhaps to clarify the discussion. We need to separate these results of model experiments - of course that’s all they are are experiments with models, from scenarios of how CO2 will increase. These are two separate issues. As far as I can tell from the IPCC report, their estimate or their numbers for the what is call the “climate sensitivity” that is, how much temperature rise will be produced by doubling of CO2 alone, all other things being equal, has not changed since 1990. It is still estimated to be between 1.5 and 4.5 °C for a doubling of CO2. And what Roy has addressed here is the fact that this is probably a faulty estimate because they have not taken into account the reduced feedback, perhaps even negative feedback, of water vapor and reduced, perhaps even negative feedback of clouds. So the climate sensitivity is the one we are interested in. I think many of us believe that these numbers, that the IPCC has given, are just plain wrong.
MR. ADLER: Any other questions?.
Q: Malcolm Ross: What about the growing sunspot numbers. There seems to be very high correlation with temperatures. And this seems to be ignored along with --
DR. SPENCER: From what little I've looked at that, I haven't been real convinced of the connection between the sunspot number and the temperature records. I think the correlation -- you know, when you've only got a couple of cycles to look at, you've got, you know, you've have the possibility for just an accidental correlation. Also, you know, the change in solar radiation during the solar cycle is only a tenth of a percent which is just awfully small. You know, what we are talking about here is forcings more on the order of a percent. So I just don't see what the connection would be. Although I never say that something's impossible unless, you know, I've really studied it. And even then it's a matter of how much I'm convinced rather than when I'm totally convinced. But, no, I don't place much emphasis on solar variation.
MR. ADLER: Thank you, Dr. Spencer. If you'll give him a round of applause.