Research Features

Forcing Agents Underlying Climate Change: Page 3 of 11

Oral Response to Senators Questions

The Chairman: My question is, were hundreds of scientists never asked? Was it changed in Shanghai? Was there pressure brought to bear on those who were drafting the report?

(The chairman was questioning in a general way the nature of the Intergovernmental Panel on Climate Change (IPCC) report and the process by which it was developed. Several of the other witnesses responded to the question.)

The Chairman: Dr. Hansen.

Dr. Hansen: That is a very difficult question. The IPCC is carrying out a very necessary process, and the technical work is superb. It involves a large number of outstanding scientists, and I am in no way critical of those scientists, but I must say I have a significant degree of discomfort with the extrapolation of the science into policy directions, the close interconnecton of the IPCC and the Kyoto discussions.

I also think that a large committee is seldom the best approach for determining actions. I do not feel that I have a prescription or that I know the best procedure to do this, but I felt much more comfortable with the assessment 20 years ago when it was done by the National Academy of Sciences, a stellar committee chaired by Jule Charney of MIT, who stayed away from policy but gave an outstanding scientific assessment.

So I do not have a very good answer to that, but I feel some discomfort about it.

The Chairman: Thank you. I would like to ask one more question of the panel, and this is something which I am sure will not be an easy one or a comfortable one for you to respond to. I want you for a moment to put yourself in the shoes of the legislator. We have now received numerous reports. We now have cumulative evidence that there is climate change. We have had some disagreements on what should...

(There were extensive replies by the other witnesses, covering five pages in the meeting transcript.)

Dr. Hansen: I agree that first of all we should take the steps that have other benefits and, in fact, I think these may take us most of the way and perhaps all of the way to what we need. I refer particularly to pollution, the examples I gave with regard to air pollution. Also, we need to support energy efficiency and alternative energies, because of the strategic value they will have with regard to our energy independence. Secondly, we should make the measurements that are necessary so we can understand what is really happening to the climate system. Third, we need to adapt the approach as we go along. This is a long-term issue.

The Chairman: Thank you. There is a vote on...


Senator Brownback: Others? Dr. Hansen, did you have any thoughts on this, perchance?

(The topic was possible government incentives for no-till agriculture and for reforestation.)

Dr. Hansen: Well, on the face of it they are both commendable activities. It does depend upon the kind of detail we were just hearing about, and I think it is important to quantify the degree to which these other benefits, in addition to reducing CO2 in the air, are in fact realized. We need to have a good cost-benefit analysis. Even though I am from Iowa, I do not claim to have expertise on exactly what the impact will be of either the no-till or the reforestation, because of these possible indirect effects. So I cannot really say much now that can help you.

Senator Brownback: The final question I want to ask, Dr. Hansen, you mentioned something about a clean coal type of technology, and I think this is also in another testimony, where you actually capture CO2 at the end of the pipe, I guess, and store it, is that correct?

Dr. Hansen: Yes. The danger with coal is that it is by far the largest potential source of atmospheric CO2, with about 10 times as much as oil and gas. So you have to be very careful about introducing greater coal use. We can reduce the black carbon probably fairly easily, that is the soot, with more efficient burning and filters on the smokestacks. In fact, that would do some good, but if we then start burning so much coal that we are producing more and more CO2, that would be counterproductive. So it is, I think, important to explore this possibility of zero emissions coal, but again I am not an expert on that.

I have heard that Germany, Japan, the United States, all are working toward that type of technology, and there have been some impressive presentations about that. It really needs to be looked at, because if that were possible--

Senator Brownback: That solves a lot of our problems.

Dr. Hansen: It does solve a lot of our problems, but it (sequestration) is bound to increase the cost of coal use, so is China going to take that extra step to capture CO2? They have a lot of coal. So it is an open issue. I think it really needs to be looked at pretty hard.

Submitted Response to Post-hearing Questions

1) You mentioned that your alternative scenario assumes that air pollution is not allowed to get any worse than it is today and that global use of fossil fuels will continue at about today's rate. It also assumes no net growth of the other forcings.

a) What are those other forcings?

They are included in Figure 2 of my submitted testimony. Chief among them are methane, tropospheric ozone and black carbon (soot) aerosols.

b) Does the IPCC business as usual scenario assume that air pollution is stable?

No. They have ozone and methane increasing substantially. In addition, they grossly underestimate the climate forcing by black carbon, and thus their scenarios tend to ignore it. Since air pollution is excluded from the Kyoto Protocol, it receives little attention in the IPCC scenarios.

c) Do these differences in assumption account for the differences in expected temperature increases in the next 50 years for the two scenarios? And again what are the temperature differences?

As shown in Figure 5 of my submitted testimony the additional warming in the next 50 years is about 1.6C in the business-as-usual scenario and about 0.75C in our alternative scenario. Moreover, the business-as-usual scenario "builds in" a much larger later warming, which will appear in the latter half of the century.

The smaller warming in the alternative scenario is due to the two assumptions: (1) it will be possible to stop further growth of non-CO2 forcings (loosely labeled "air pollution"), particularly ozone, black carbon and methane, (2) it will be possible to keep the growth of atmospheric CO2 to about 75 parts per million in the next 50 years, which would require that CO2 emissions remain roughly similar to today's rate or decline slightly.

2) You mentioned in your statement that the judge of science is observations. You also mentioned the potential educational value of keeping an annual public scorecard of measured changes. Can you elaborate on this idea?

It is briefly elaborated upon in reference 22 of my submitted testimony, where I mention an annual public scorecard of (1) fossil fuel CO2 emissions, (2) atmospheric CO2 amount, (3) human made climate forcing, (4) global temperature. I will try to write a paper with a more comprehensive discussion in the near future. One obvious addition would be an annual measure of CH4 emissions and atmospheric amounts. However, the single most important benchmark for the United States is probably an annual update of the bar graph in Figure 11 of my testimony, i.e., the annual growth of CO2 emissions: the annual growth needs to be reduced to zero or slightly negative.

3) Do you feel that your results were reviewed and properly considered as part of the IPCC process?

No. IPCC's size and review procedures make it inherently lethargic, so responding to a mid-2000 paper is difficult. However, the real problem is probably the close binding between IPCC and the Kyoto Protocol discussions. Kyoto excludes consideration of air pollution (such as tropospheric ozone and black carbon), for example, so IPCC basically ignores these topics and downgrades them. The only IPCC "review" of our paper was by the IPCC leaders (as reported in the New York Times, for example), who saw our paper as potentially harmful to Kyoto discussions. They received the backing of organizations (such as the Union of Concerned Scientists, who commissioned a criticism of our paper that I respond to in reference 22) and publications (particularly Nature), who had previous editorial positions favoring the Kyoto Protocol. When I had difficulty publishing a response in Nature, I wrote an open letter that is available at

4) You mentioned that the climate cannot respond immediately to a forcing because of the long time needed to warm the oceans. How would we measure the real impact of reducing the amount of greenhouse gases in the atmosphere in the short term?

We should of course measure the individual greenhouse gases as the best measure of short-term effectiveness of any attempts to reduce emissions. However, the best measure of the impact of the net climate forcing is likely to be heat storage in the ocean. Natural variations of this rate will occur because of the dynamics of the system, but if the measurements are accurate and maintained for years they will soon begin to provide us with a great tool for understanding where the future climate is heading.

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