Mr. MEYER. A $25 a ton tax applied across the board would raise about $140 billion a year. The CHAIRMAN. $140 billion? Mr. MEYER. Yes. This is carbon, not CO2 I should point out. It is equivalent to about an $80 tax in carbon dioxide. This is per ton of carbon. The CHAIRMAN. It is about $140 billion, though. Mr. MEYER. Yes. It is equivalent to about $92 per ton of carbon, $25 per ton of CO2. Excuse me. The CHAIRMAN. Senator Wallop? Senator WALLOP. Thank you, Mr. Chairman. Mr. Meyer, are you a meteorologist? Mr. MEYER. No, I am not. Senator WALLOP. Are you an economist? Mr. MEYER. My training was in economics and political science at Yale. Yes. Senator WALLOP. So, as a concerned scientist, you are a political scientist? Mr. MEYER. And economist, yes. Senator WALLOP. Well, we had four meteorologists in here of varying views amongst themselves, so varying in fact that the only common denominator amongst them was the uncertainty of the science regarding this issue of global climate change. When you are talking about climate stabilization, how do you distinguish between natural change and that caused by man? Mr. MEYER. What we were saying is basically what is needed to achieve the kind of reductions in CO2 emissions since we were looking specifically at that greenhouse gas, what is needed in reductions in emissions of that to stabilize concentrations based on the IPCC's analysis of stabilization. Senator WALLOP. The Schlesinger/Jiang 1991 article in Nature magazine using the mid-range estimate by the IPCC, said that deferring a reduction of CO2 by 10 years-I mean, deferring a reduction, not reducing it, deferring it—would change the 2100 year, 21st century, temperature rise by less than a tenth of a degree Centigrade. Their point is that maybe waiting on good science would not be too radical. [The article follows:] Revised projection of future greenhouse warming Michael E. Schlesinger & Xingjian Jiang Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, 105 South Gregory Avenue, Urbana, Illinois 61801, USA FOR the Intergovernmental Panel on Climate Change (IPCC) report', using a simple climate/ocean model, we made projections of the greenhouse warming to 2100. Projections were made for four greenhouse-gas scenarios, whose radiative effects in 2100, expressed in terms of an equivalent amount of CO2, ranged from 2 to 5.5 times the pre-industrial CO2 concentration. The projected global warming in 2100 for these scenarios, relative to 1990, ranged from 0.62-2.31 °C for the minimum assumed CO2-doubling temperature sensitivity, AT2 = 1.5°C, to 1.61-5.15 °C for the maximum sensitivity AT2 = 4.5 °C. Here we broaden these projections to include a recently suggested lower sensitivity, AT2 = 0.5°C. We also revise all projections by prescribing, using the results of our analysis of simulations by a coupled atmosphereocean general circulation model, a lower value for a key parameter of the simple ocean model, II, which indicates the warming of the polar ocean relative to the warming of the non-polar ocean. We find that, for any value of AT2, the atmospheric temperature increases more rapidly with time as a consequence of the reduction in II. We also find that a delay of ten years in initiating a 20-year transition from the IPCC business-as-usual' scenario to any other TPCC scenario has only small elect on the ected warming in 2100, regardless of the t *. This indicates that the penalty for a 10-year delay is small. Our earlier analysis for the IPCC report, and this revision thereof, both use an energy-balance climate/upwellingdiffusion ocean model (Fig. 1) similar to that introduced by Hoffert et al.2 and used by Hoffert and Flannery3 to predict CO2-induced climate change. This simple climate/ocean model LETTERS TO NATURE is used instead of our atmosphere-ocean general circulation model because of the latter's large computational requirement. The simple climate/ocean model (Fig. 1) determines the surface temperature of the atmosphere and the temperature of the ocean as a function of depth from the ocean surface to the ocean floor. In the model, the ocean is subdivided vertically into 40 layers, with the uppermost being the mixed layer and the deeper layers each being 100 m thick. The ocean is also subdivided horizontally into a polar region where bottom water is formed, and a non-polar region where there is vertical upwelling. In the non-polar region, heat is transported upwards toward the surface by the upwelling, and downwards by physical processes whose effects are treated as equivalent to diffusion. Heat is also removed from the mixed layer in the non-polar region by transport to the polar region and downwelling towards the ocean bottomthis heat is ultimately transported upwards from the ocean floor in the non-polar region. Five quantities must be prescribed in this simple climate/ocean model: the temperature sensitivity of the climate system, characterized by the equilibrium warming induced by a CO2 doubling, A T2x; the vertically uniform upwelling velocity for the global ocean, W; the vertically uniform thermal diffusivity, κ, by which all non-advective vertical heat transport in the ocean is parameterized; the depth of the oceanic mixed layer, h; and the warming of the polar ocean relative to the warming of the non-polar ocean, ПI. For the IPCC report we chose three values of AT2x (4.5, 2.5 and 1.5 °C) and h = 70 m, W = 4 m yr, x = 0.63 cm s, and II 1.0. We chose the latter value as a result of simulations by atmospheric GCM/mixedlayer ocean models of the equilibrium climate change induced by a doubling of the atmosphere CO2 concentration'. These simulations show a poleward amplification of the surface temperature change in the winter hemisphere, thereby suggesting that II should equal 1.0. Here we prescribe II based on our recent analysis* of the transient time evolutions of 1×CO2 and 2×CO2 simulations with an atmosphere-ocean GCM. Examining the changes in temperature in the polar (downwelling) and non-polar (upwelling) regions gives values of II that range from 0.569 for the uppermost layer (a depth of 0-50 m) to 0.004 for the lowermost layer (a depth of 2,750-4,350 m), with a depth-averaged value of 0.161. The smallness of the depth-averaged value and the value of II for the deep ocean are probably due to the brevity of the 1 x CO2 and 2 × CO2 simulations, each being only 20 years W Polar region Non-polar region FIG. 1 Schematic representation of the energy-balance climate/upwellingdiffusion ocean model. LETTERS TO NATURE TABLE 1 Potential warming reduction in 2100 obtained by a linear transition from IPCC scenario A to IPCC scenario B, C or D during either 1990-2010 long. It is therefore likely that 0.161<II<0.569, with a value closer to the mean of 0.365, and we accordingly choose II = 0.4. We have calculated the temperature change from 1765 to 1990 induced by the historical evolution of greenhouse gases (T. Wigley, personal communication), and from 1990 to 2100 for the four IPCC scenarios. These scenarios can be characterized by the year in which the radiative effect of greenhouse gases is equivalent to a doubling of the pre-industrial CO2 concentration: A ('business-as-usual'), 2015; B, 2031; C, 2038 and D, 2100. We have performed these calculations for presumed temperature sensitivities of AT2x=4.5, 1.5 and 0.5 °C, the first two values being the extremes adopted by IPCC, and the latter value proposed by Lindzen (and personal communication, 1990). Comparing the calculated greenhouse-induced temperature changes for these different sensitivities with the observed global mean temperature changes from 1880 to 1990 (ref. 1) shows that the patterns of temperature change are not identical in shape or magnitude (Fig. 2). In particular, the calculated temperature changes increase monotonically in time and attain values of 1.30, 0.61 and 0.24 °C in 1990 relative to 1880 for the three sensitivities, respectively, but the observed global mean temperature does not increase monotonically in time, and is ~0.5 °C in 1990 relative to 1880. Thus, there are significant disparities between the observed and reconstructed temperature evolutions for both AT2x=4.5 and 0.5 °C, with a best fit being obtained for AT2x=1.24 °C, a value less than the minimum temperature sensitivity used in the IPCC calculations. This sensitivity is also below that for zero feedback (only radiative-convective adjustment of temperature without changes in other quantities such as water vapour, clouds and sea ice), (AT2x)o=1.32 °C, and implies a net negative feedback of ƒ = −0.06 [AT2x/(AT2x)0= 1/(1-)]. But as discussed by Wigley and Raper', it is difficult to estimate AT2x from the observed temperature record because of the unknown contribution from the climate's natural variabil 1.4 ity. Any estimate of AT2, is further confounded by external forcing mechanisms, both natural (for example, volcanic and solar-irradiance variations) and anthropogenic (for example, sulphate emissions), the magnitudes of which are also uncertain. Our temperature projections to 2100 for the IPCC scenarios using II = 0.4 give larger temperature increases than those using II=1.0, with the difference being larger for larger AT2. This occurs because less heat is transferred to the deep ocean as II decreases, hence the warming of the upper ocean and atmosphere increases. For the business-as-usual scenario (A) and with AT2x=4.5 °C, T(2100) - T(1880) = 6.2 °C for II = 1.0, but 7.2 °C for II=0.4. The corresponding values for AT2 = 1.5 °C are 2.9 °C and 3.1 °C, whereas those for AT2x=0.5 °C are both 1.1 °C. These results clearly show that the magnitude of the potential greenhouse-gas-induced climate change ranges from catastrophic to minor depending on the true value of AT2, for the climate system. Consequently, it is imperative to narrow the range of possible values of AT2x, for example, by determining the minimum possible value below which the Earth would not have undergone glacial-interglacial cycles. This can be done by model simulations of these cycles and comparison with paloclimate data. We have calculated the temperature changes from 1990 to 2100 for the IPCC scenarios B, C and D, in which greenhouse gas emissions are reduced. These calculations show, as did our IPCC calculations, that reducing the future increase in greenhouse gases reduces the future increase in temperature, with the size of the reduction being larger for larger AT2x. For example, the 1990-2100 temperature rise for scenario B is less than that for scenario A by 2.45, 1.08 and 0.40 °C for AT2x=4.5, 1.5 and 0.5 °C, respectively. If a linear transition from 1990 to 2010 is 2.5+ made from the emission rate of scenario A to the emission rate of scenario B, the reduction in temperature rise in 2100 is 2.31, 1.04 and 0.39 °C for AT2x = 4.5, 1.5 and 0.5 °C, respectively (Fig. 3, Table 1). If the initiation of this transition in emission rate is deferred 10 years until 2000, the reduction in temperature rise in 2100 is 2.18, 0.99 and 0.37 °C; that is, at least 95% of that possible by not deferring the transition. The equivalent atmosphere CO2 concentration in 2100 increases as a consequence of this deferral, thereby increasing the equilibrium temperature change (the committed warming,' approximately equal to the increase in temperature change shown in Fig. 3) by 0.15, 0.05 and 0.02 °C for AT2x = 4.5, 1.5 and 0.5 °C, respectively. Corresponding results are obtained for 20-year linear transitions from the emission rate of scenario A to the emission rate of either scenario C or scenario D (Fig. 3), with the reduction in temperature rise in 2100 equal to at least 95% of that possible by not deferring the transition, regardless of the temperature sensitivity (Table 1). The corresponding increases in the committed warming in 2100 for a 10-year deferral in transitions from scenario A to C(D) are 0.22(0.28), 0.07(0.09) and 0.02(0.03)°C for AT2x=4.5, 1.5 and 0.5 °C, respectively. This indicates that the penalty is small for a 10-year delay in initiating the transition to a regime in which greenhouse-gas emissions are reduced. To us this small penalty does not indicate that we should 'wait and see' and do nothing during this decade-quite the contrary. The study of the greenhouse effect, both theoretically and observationally, should be accelerated into a 'crash programme' so that we do not squander the time that nature has given us to obtain a realistic understanding of the climate response to increasing concentrations of greenhouse gases.☐ Received 12 November 1990; accepted 28 January 1991. 1. Houghton, J. T., Jenkins, G. J. & Ephraums, J. J. (eds) Climate Change: The IPCC Scientific Assessment (Cambridge University Press, 1990). 2. Hoffert, M. I., Callegari, A. J. & Hsieh, C.-T. J. geophys. Res. 85, 6667-6679 (1980). 3. Hoffert, M. I. & Flannery, B. P. in Projecting the Climatic Effects of Increasing Carbon Dioxide (eds MacCracken, M. C. & Luther, F. M.), 149-190 (US Department of Energy, Washington, DC 1985). 4. Schlesinger, M. E. & Jiang, X. J. Clim. 3, 1297-1315 (1990). 5. Schlesinger, M. E. & Mitchell, J. F. B. Rev. Geophys. 25, 760-798 (1987). 6. Lindzen, R. S. Bull. Am. meteorol. Soc. 71, 288-299 (1990). 7. Wigley, T. M. L. & Raper, S. C. B. in Greenhouse-gas-induced Climatic Change: A Critical Appraisal of Simulations and Observations (ed. Schlesinger, M. E.) 471-482 (Elsevier, Amsterdam, 1991). 8. Charlson, R. J., Langner, J & Rodhe, H. Nature 348, 22 (1990). ACKNOWLEDGEMENTS. This research was supported by the US NSF and the US Department of Energy, Carbon Dioxide Research Program, Office of Health and Environmental Research. Mr. MEYER. Let me just say we do not believe we are proposing anything which we should not be doing anyway. We believe truly that the measures we are talking about are a no regrets kind of strategy. They are things we ought to be doing in light of what we know now, and they are certainly things that are worth doing to avoid, as I said, the future risk. It is a very cheap insurance premi um. Senator WALLOP. One of the things you said you are worried about is increased oil imports. Why does the union oppose domestic production? Mr. MEYER. We do not oppose domestic production if it is done consistent with environmental protection and wilderness values. I think there are Senator WALLOP. That is opposition to domestic production. Mr. MEYER. I do not think it has to be. Senator WALLOP. It has not gotten around to the point where we can do it. Mr. MEYER. No. I do not think it has to be, Senator. If you look at the NES, the projections for enhanced oil recovery and tertiary recovery are about 10 times that, for example, of the Arctic Wildlife Refuge. So, I think the debate has gotten polarized on these very environmentally sensitive and controversial production initiatives, and we may be ignoring something that is not quite as controversial that can provide a lot more energy in the long run. Senator WALLOP. Well, the CONSAD study is being released today with regard to your carbon tax. [The study follows:] |