| COMMENTARY Three Inconvenient Truths About Global Warming
Robert Ehrlich
As my friend Art Hobson notes in the July 2007 issue of Physics & Society, it is becoming increasingly clear that it is not possible to curb global warming completely. Hobson cites a 2006 study1 led by former World Bank Chief Economist, Nicholas Stern, which notes that stabilizing atmospheric CO2 levels at 450 ppm would cost the equivalent of a reduction of world GNP of one percent for many years. According to Hobson, the Stern study notes that “while if not addressed adequately it will cost 20 percent of world GDP” (now and forever!). As physicists, we are trained to spot numerical comparisons that seem so out of bounds as to be incredible, so I was prompted to look up the Stern study. The report contrasts “no action” to curb global warming (which is clearly not a realistic course of action), with the actions needed to reach the 450 ppm stabilization level. Moreover, the Stern report makes certain economic assumptions, including an extremely low “discount rate”2 and a severe aversion to income inequalities between nations and between generations that may be justified on ethical grounds, but which depart from what is assumed in mainstream economic models, and in the real world as well.2,3 The more interesting choice, however, is not between no action and a crash program for dealing with global warming, rather; it is between the various strategies for dealing with the problem. These range, for example, from steep carbon taxes that Hobson advocates to taking only those cost-effective actions, such as energy conservation and deploying green energy alternatives as they become cost competitive. An excellent perspective on the relative merits of these strategies can be understood by reading the 2007 report 4 of the IPCC. That report notes it would cost up to $18 trillion U.S. dollars to eventually stabilize atmospheric CO2 concentrations at the level of 450 parts per million (ppm), which still would cause a temperature rise by 2100 of around 1.7 degrees Celsius. (Incidentally, $18 trillion does somehow sound more impressive than one percent of World GNP for 30 years!) A more gradual approach (which allowed world (not U.S.!) emissions to increase for another 50 years before reducing them) would lead to an atmospheric stabilization level of 750 ppm. Surprisingly, the temperature rise by 2100 would not be very much higher (around 2.5 degrees Celsius) under this scenario – perhaps surprising in light of the 67% higher CO2 stabilization level.. (Both projected temperature rises have large associated uncertainties.) According to the IPCC report, stabilization at the higher 750 ppm CO2 level should cost at most 5 percent as much as the 450 ppm level (and possibly as little as zero), because it involves actions that pay for themselves. Thus, in evaluating the tradeoff between these two possibilities, one needs to ask how important is it to pay up to $200 billion cummulatively to cool the planet by each 0.01 degree reduction from the 2.5 degrees projected under the 750 ppm level? It could be very detrimental to allow the rise to exceed say 2 degrees, if there really were any evidence this value represented a dangerous threshold or a “tipping point.” But, even if we acknowledge that larger degrees of harm result from higher temperatures, and that tipping points might exist, there is no evidence for 2 degrees Celsius being such a threshold, despite some expressed opinion to the contrary. (Others, including James Lovelock,5 author of the Gaia Hypothesis, have claimed we are already past the tipping point.) There simply is no evidence for Hobson’s assertion that another 0.75 degree increase “beyond the 1.25 degrees that is already ‘in the pipeline’ because of the delayed effects of the global warming pollutants already in the atmosphere will cause the polar ice cap melting to begin.” Pretending otherwise is not science; it is scare-mongering in pursuit of a political objective. In fact, from the perspective of those wishing to portray global warming as an urgent problem, a 2 C tipping point is a "Goldilocks" value. If the tipping point was 1.25 C i.e. only 0.75 C less, nothing could be done now to avert disaster -- even cutting CO2 emissions to zero. Were the value only 0.75 C more (2.75 C), global warming becomes a non-urgent matter better solved on a gradual long-term basis. Given the failure of the IPCC to define the "dangerous interference with the climate system" that must be avoided according to the Rio Climate Treaty, could this claimed 2 C tipping point have been simply chosen to convince policymakers and the public of the urgency of the problem? (Aside from the possibility that this value has been chosen by God in order to get humanity to see that it must band together now to save the planet, it seems likely that the choice was made by humans on the basis of politics, rather than science.) I do nevertheless applaud some of Hobson’s suggestions, including these: increase nuclear power threefold to displace coal; increase wind power 40-fold to displace coal; increase solar power (photovoltaics, solar-thermal electricity generation) 700-fold to displace coal; increase wind power 80-fold to make hydrogen for zero-emission cars – although I think these should be achieved gradually. But some other suggestions I find unwise. Ethanol, for example, is simply not practical, in terms of the arable land required, the ground level pollutants created, the impossibility of supplying enough ethanol for two billion cars, and the better alternatives available. Likewise, while it is nice to live in an area where one can walk to work, bicycle to work, or live near your work, for the foreseeable future, this does not apply to most Americans, who will probably not welcome the higher gasoline taxes Hobson feels are necessary. Higher gasoline prices might be a good thing, but in all likelihood, rising market prices will do that job all on its own without the necessity of steep carbon taxes. (A modest carbon tax, in contrast, would be far less disruptive to the economy, and could bring about the needed gradual transition to a more energy efficient society.) Thus, in summary, I believe that we need to face altogether three inconvenient truths about global warming: (a) it is real and could be very serious in the future, (b) curbing it significantly would not be inexpensive and would still lead to a significant temperature rise over the next century, and (c) while the possibility of harm clearly increases along with the magnitude of the temperature increase, we currently have no clear line as to what level is “dangerous,” or what might be the threshold of any alleged “tipping points.” Footnotes: 1. Nicholas Stern, The Economics of Climate Change: The Stern Review (Cambridge University Press, Cambridge, UK, 2007. 2. The discount rate in economic theory refers to the real return on capital. It influences the determination of the optimum balance between emissions reductions today and the benefit of future mitigation of damages. The benefit of future mitigation also in turn depends on the relative importance we attach to the welfare of society today, and that in future generations, including the distant future. It also in turn depends on our assessment of the likelihood that other possible catastrophes such as a nuclear war or a mass epidemic may occur which might lead to severe depopulation that could make global warming a much less urgent problem. It is noteworthy that half of the estimated economic damages due to global warming estimated in the Stern Report methodology occur after the year 2800. 3. William Nordhaus, “Critical Assumptions in the Stern Review on Climate Change,” Science, 317, 2007 201-202. 4. The 2007 Working Group III Report "Mitigation of Climate Change" may be downloaded free of charge from: http://www.ipcc.ch/ 5. James Lovelock, The Independent, January, 2006. Lovelock in his 2006 book “Revenge of Gaia” makes the case that mankind’s only hope of avoiding catastrophe is a massive shift from fossil fuels to nuclear energy, and that all other alternative energy choices will not allow us to make the needed emissions reductions in time.
Robert Ehrlich
George Mason University
Fairfax, VA 22030
rehrlich@gmu.edu
|