by Judith Curry
There was some discussion of this topic in the context Murry Salby’s talk, but it has been suggested that this topic deserves its own thread.
This post is motivated by the following email from Hal Doiron:
Hello Dr. Curry,
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In my review of climate change literature related to atmosphereic CO2 sources and sinks, I have run into a wide range of opinions and peer reviewed research conclusions regarding the following specific question that I think is central to the CAGW debate.
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How long does CO2 from fossil fuel burning injected into the atmosphere remain in the atmosphere before it is removed by natural processes?
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Sources of confusion in answering this question:
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1. In responses to one of my comments at Climate, Etc., Fred Moolten has claimed the answer to this question is about 100 years. http://judithcurry.com/2011/08/18/should-we-assess-climate-model-predictions-in-light-of-severe-tests/#comment-101642 “To focus on the most relevant element in this situation, CO2, the salient feature is the exceedingly long lifetime of any atmospheric excess we generate from anthropogenic emissions – there is no single decay curve, but the trajectory of decline toward equilibrium concentrations can be expressed as a rough average in the range of about 100 years, with a long tail lasting hundreds of millennia. In other words, the CO2 we emittomorrow, or refrain from emitting, is not something we can take back if we later decide we shouldn’t have put it up there. It will warm us for centuries.”
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2. From an ESRL NOAA website http://www.esrl.noaa.gov/gmd/education/faq_cat-1.html#17 , I found:
· What will happen to Earth’s climate if emissions of these greenhouse gases continue to rise?
Because human emissions of CO2 and other greenhouse gases continue to climb, and because they remain in the atmosphere for decades to centuries (depending on the gas), we’re committing ourselves to a warmer climate in the future. The IPCC projects an average global temperature increase of 2-6°F by 2100, and greater warming there after. Temperatures in some parts of the globe (e.g., the polar regions) are expected to rise even faster. Even the low end of the IPCC’s projected range represents a rate of climate change unprecedented in the past 10,000 years.
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3. I believe in listening to Dr. Murry Salby’s audio lecture at Climate, Etc., his research led him to the conclusion that the atmospheric residence time of CO2 from fossil fuel burning emissions was only a few years. This was related to investigation of the trends of the ratio of Carbon 12 to Carbon 13 isotopes in the atmosphere.
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4. There is previous published literature, also based on the ratio of Carbon 12 and Carbon 13 isotopes that Dr. Salby discussed, that concludes the atmospheric residence time of CO2 from fossil fuel burning is about 5 years. This literature is reviewed and cited by my former NASA colleague, Apollo 17 astronaut, and former US Senator, Dr. Harrison “Jack” Schmitt, in his essay on CO2 at: http://americasuncommonsense.com/blog/category/science-engineering/climate-change/4-carbon-dioxide/#r4_14
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As I monitor the debate on CAGW, it seems to me that if this particular recommended thread topic could be settled with high confidence, then much of the CAGW alarm could be moderated and refocused on a broader range of climate change issues. I suggest it should also be a key research topic for further investigation in an attempt to answer the posed question with high confidence.
Sincerely,
Hal Doiron
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JC comment: I don’t have a good answer to the question Hal raises. Below are some online references that I’ve spotted, from across the spectrum.
- Residence Time of Atmospheric CO2, H. Lam of Princeton
- Wikipedia
- SkepticalScience
- CO2 Science
- Appinsys
- Robert Essenhigh
And finally an exchange between Freeman Dyson and Robert May in the NY Review of Books:
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I don’t have time to dig into this issue right now, so I’m throwing the topic open for discussion, hoping for some enlightenment (or at least confusion) from the Denizens.