David R. Henderson  

We Calculate: You Decide

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Patrick J. Michaels and Paul C. "Chip" Knappenberger have figured out a marvelously clever way of showing the effects of various levels of carbon reduction on the temperature 2050 and by 2100.

They use a term called "climate sensitivity" and explain:

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.

They start by asking you to key in whether you apply a reduction in carbon just to the United States or more broadly. Then they ask you to choose by how much to reduce carbon. Finally, they give you the option of a range of climate sensitivities. Voila. Out pops the answer. I don't want to spoil your fun, so have at it.

Update: The above was corrected based on a correction provided to me by Bob Murphy.


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COMMENTS (6 to date)
Douglass Holmes writes:

Wow. If we all reduced our carbon emissions 100%, we could shave 1/3 of a degree off by 2100. Does anyone think that we could do that without some economic cost?

Chris H writes:

Technically speaking, isn't the point of a Pigovian tax not to eliminate an externality's effects, but to internalize the cost of them? In that regard, preventing climate change is not the primary goal of a well-designed carbon tax (at least from an economic point of view). On the other hand, this should factor into what is an appropriate level for internalizing the externality. If the sum total of all carbon usage in the developed world is about a third of a degree of temperature under worst case scenarios, doesn't that then imply that the cost imposed by additional units of carbon being emitted should be rather low?

Also why is this effect so small? Is the rise of industrializing nations offsetting this or are emissions that have already been put out of much greater importance than any new emissions?

Finally, given the interconnectedness of world markets, is this model taking into account that reduce fossil fuel demand in the US and the rest of the developed world would drop prices meaning developing countries could simply pump out carbon that's being taxed in developed countries? If the model isn't taking this into account then isn't it implicitly over-estimating the climate mitigation effects of a US or developed world carbon tax?

Daublin writes:

I really like this line of argument. The policy aspects of CO2 emissions are much more damning than the scientific aspects.

Part of the problem is that the policy options widely discussed just don't matter much, even if you accept Hansen-like CO2 sensitivity.

A more subtle problem, but more damning, is that you can't stop CO2 emissions by reducing them. Maybe that sounds silly, but if all we do is switch from driving cars to riding on trains, at best we are delaying the forecast for a CO2 catastrophe. If the CO2 catastrophe is real, then we need to not just ditch cars; we need to all stay home. Driving fancy low-emission cars is not a step on the way to victory; it actually kinda entrenches doing things the wrong way.

william occam writes:

is the Co 2 reduction immediate or is it achieved by 2050?

Thomas Nagle writes:

http://harvardmagazine.com/2013/07/buffering-the-sun
The current issue of Harvard Magazine has a great article on serious options being considered to "engineer" a reduction in global temperatures without having to eliminate carbon emissions. Interesting how the Harvard author of the article is almost apologetic that such research is going on at Harvard but argues that if "skeptics" prevent us from reducing carbon emissions then we "have to have a Plan B". In any case, just like we have managed to deal with all the other changes man has made to the environment, we can find ways to manage temperature.

ThomasH writes:

Good analysis which also shows that nothing bad happens if you don't vote.

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