The Current Wisdom is a series of monthly articles in which Patrick J. Michaels, director of the Center for the Study of Science, reviews interesting items on global warming in the scientific literature that may not have received the media attention that they deserved, or have been misinterpreted in the popular press. In this special issue, we focus on the climate implications of a carbon tax.



the carbon dioxide emissions reduction amount (calculated from the 2005 baseline) that will take place by the year 2050 (and remain in place thereafter), the region which will take part in the emissions reduction plan (the United States, or for the more optimistic, the industrialized nations of the world), and the climate sensitivity (how much you think the global average temperature will increase as a result of a doubling of the pre-industrial atmospheric carbon dioxide concentration). The United Nation’s Intergovernmental Panel on Climate Change’s (IPCC) modestly-educated guess is 3.0°C, but a collection of reports from the recent scientific literature puts the value around 2.0°C, and based on recent global temperature behavior, a value of 1.5°C may be most appropriate. Not wanting to leave firebrands like former NASA employee James Hansen out of the fun, we include the option of selecting an extremely high climate sensitivity value of 4.5°C.

A year ago, July 23, 2012 to be precise, former Republican congressman Bob Inglis famously predicted the facts on global warming will “overwhelm” GOP resistance to climate change action and alter the party’s stance. In response, he proposed a carbon tax.That’s the kind of thing that always pops up during the hottest time of the year, which is late July, and it’s again in the public yakstream.Inglis is “former” because he lost his primary in a heavily Republican South Carolina district by an unprecedented—for an incumbent congressman with no scandal—70-29 margin, and he (correctly) blamed his defeat on his newly-found perseveration on global warming.Since then, he has associated with R-Street Partners, which calls itself a libertarian think tank, but which is very vocal in support of his tax.So, as discussions of a carbon tax continue in the halls and chambers of Washington, we provide a handy tool for tax fans to determine the global warming “savings” from whatever emissions reduction their hearts desire.We leave it to the user (policymaker, Congressman, former Congressman, think tank scholar, President, voter, etc.) to decide how much of a carbon tax should be levied to produce the desired result.Using our calculator, you can specify

We calculate, you decide.



Once you make your selections, the calculator will return the amount of global temperature rise that will be averted as a result of your choices by the year 2050 and also by the end of the century.



Try it using this example. Choose a 100% reduction of carbon dioxide emissions from the United States and the IPCC’s sensitivity value of 3.0°C. Hit “Submit.” The amount of temperature savings that results is 0.052°C by the year 2050 and 0.137°C by the year 2100. (Why we are using three significant digits is in the fine print at the end of this article.)



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Sorry, Major Kong (h/t to “Dr. Strangelove”), those are the figures. That’s the right answer. Assuming the IPCC’s value for climate sensitivity (i.e. disregarding the recent scientific literature) and completely stopping all carbon dioxide emissions in the U.S. between now and the year 2050 and keeping them at zero, will only reduce the amount of global warming by just over a tenth of a degree (out of a total projected rise of 2.619°C between 2010 and 2100).



If you think that a rise of 2.482°C is vastly preferable to a rise of 2.619°C then all you have to do is set the carbon tax large enough to drive U.S. emissions to zero by mid-century—oh yeah, and sell that tax to the American people.



To explore other alternatives, use our handy-dandy calculator.



Have fun!



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The fine print:



The results from our calculator are produced from climate change calculations performed using the MAGICC climate model simulator (MAGICC: Model for the Assessment of Greenhouse-gas Induced Climate Change). MAGICC was developed by scientists at the National Center for Atmospheric Research under funding by the U.S. Environmental Protection Agency.



We are not creative enough to have made that acronym up. MAGICC is itself a collection of simple gas-cycle, climate, and ice-melt models to efficiently emulate the output of complex climate models. MAGICC produces projections of the global average temperature and sea level change under user configurable emissions scenarios and model parameters. MAGICC is run using its default model parameter settings except for climate sensitivity, which you can choose from between 1.5°C and 4.5°C.



The baseline emissions scenario against which all climate dioxide reductions were measured is scenario A1B from the IPCC’s Special Report on Emissions Scenarios (SRES). Scenario A1B is a middle-of-the-road emissions pathway which assumes rapid carbon dioxide emissions growth during the first half of the 21st century and a slow CO2 emissions decline thereafter. Emissions are prescribed by country groups. Our “Industrialized Countries” group is the OECD90 countries (which includes North America, Western Europe, and Australia, New Zealand and Japan.) In order to obtain the baseline emissions from the United States to which the emissions reduction schedule could be applied, the U.S. emissions were backed out from the OECD90 country grouping. To do so, the current percentage of the total group emissions that are being contributed by the United States was determined—which turned out to be right around 50%. We assume that this percentage will be constant over time. In other words, that the U.S. contributed 50% of the OECD90 emissions in 2000 as well as in every year between 2000 and 2100. In this way, the future emissions pathway of the U.S. was developed from the group pathway defined by the IPCC for the A1B scenario. From these baselines (either the U.S. baseline or the OECD90 baseline), carbon dioxide emissions reductions were applied linearly from 2005 to 2050 to obtain the user-specified total reduction. The new (reduced) emissions were recombined with the other (unadjusted) IPCC country groupings to produce the global emissions total. It is the total global emissions that are entered into MAGICC to yield global temperature projections. The results using the reduced emissions pathway were then compared to the results using the original A1B pathways as prescribed by the IPCC, with the baseline against which temperature changes were calculated set to the year 2010.



We assume that a carbon tax would only be applied to reduce carbon dioxide emissions. In practice however, the only way to reduce carbon dioxide emissions is to reduce the burning of fossil fuels. Reducing the burning of fossil fuels will have co-impacts such as reducing the emissions of carbon monoxide (CO), volatile organic compounds (VOCs), nitrogen oxides (NOx), and sulfur oxides (SOx). The first three chemical compounds generally enhance warming while the latter generally retards it. Sensitivity tests using MAGICC indicate that for the OECD90 countries under the A1B pathway, the effect of collective changes in these co-emissions is largely compensative.



Additional fine print on precision: The temperature savings are presented to three significant digits in order to tell the results apart. In the real world, the impacts from the emissions reduction pathways are not nearly so precise and, in fact, the temperature savings from most of the different carbon dioxide emissions reduction pathways are scientifically impossible to tell apart from each other, and in many cases, are impossible to tell apart from the original A1B scenario, i.e., they are same thing as doing nothing.