Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”


There seems to be a noticeable murmur around town about a carbon tax—a tax on the amount of carbon dioxide that is released upon generating a unit of energy. Since fossil fuels—coal, oil, natural gas—are both the source of over 75% of our energy production and emitters of carbon dioxide when producing that energy, a carbon tax insures that the price of everything goes up.


There is one and only one justification for a carbon tax—an attempt to influence the future course of the earth’s climate (or, as some people prefer, to mitigate anthropogenic climate change) by trying to force down the emissions of the most abundant human‐​generated greenhouse gas.


But of all the things that a carbon tax will do (raise prices, increase bureaucracy, elect Tea Partiers, etc), mitigating anthropogenic climate change in any meaningful manner is not one of them.


The annual carbon dioxide emissions from the U.S., currently about 5,500 million metric tons per year, only contributes roughly 0.003°C/per year of warming pressure on global temperatures (see here for a handy way of making that calculation). So the best that a carbon tax could ever hope to achieve, climatically, would be to prevent this amount of warming each year by completely eliminating all carbon dioxide emissions from the U.S.


If we went to zero emissions tomorrow, the carbon tax would prevent about 0.26°C of global temperature rise by the year 2100. According to the latest projections from the Intergovernmental Panel on Climate Change (IPCC), the projected temperature rise by the end of the century ranges from about 1.1 to 6.4°C, with a business‐​as‐​usual rise of around 3°C (put me down for 1.6° until then, unless nature is being a blatant liar). The “mitigated” rise is proportional to the expected temperature rise. A carbon tax enacted today that is immediately and completely successful at eliminating all U.S. CO2 emission would lower rise in temperature expected by the end of the century around 10%. This amount is small, of little consequence, and in fact will be difficult to detect.


It is also not going to happen. We only have the capacity to produce about 30% of our electricity from non‐​carbon emitting fuel sources (primarily nuclear and hydroelectric). So it will take time, and probably a lot of time (many decades) before our energy needs could possibly be met without emitting CO2 into the atmosphere. And of course, as time ticks by before eliminating or at least appreciably reducing our emissions, the amount of global warming saved by such action declines (and become less and less consequential), as does the justification for the carbon tax.


I am just in the early stage of this analysis, so the numbers above are a bit rough (but conservative). In the future I hope to produce a menu of emissions reductions/​climate savings options—but one without prices. That way the policymakers will see what they are going to be getting for whatever price they decide to assign. So too will the general public. And what they will all see is that whatever level of carbon tax they decide upon, they will get a lot of climate nothing for a lot of financial something.


The best thing would be for policymakers to just leave well enough alone, for on their own, carbon dioxide emissions in the U.S. have been declining for more than a decade (and in fact are pushing levels of the early 1990s, http://​www​.eia​.gov/​e​n​v​i​r​o​n​m​e​n​t​/​e​m​i​s​s​i​o​n​s​/​c​a​rbon/). And even if such a reduction doesn’t result in any scientifically detectable climate impacts, at least it hasn’t cost us anything.