Sunday, November 30, 2014

Atmospheric Lifetime of Fossil Fuel Carbon Dioxide

Eg., those who cite a 100 year lifetime, are counting the absorption of CO2 molecules by the ocean, but not counting the release of previously absorbed CO2 molecules from the ocean back into the atmosphere. And they don't take into account that processes that remove CO2 from the air, such as absorption by the ocean, will slow in the future, as they become saturated with CO2 or used up by reactions with CO2. I will also create a post about a user-friendly book on this subject by David Arthur, one of the contributors to the technical article I cite below.

David Archer, Michael Eby, Victor Brovkin, Andy Ridgwell,
Long Cao, Uwe Mikolajewicz, Ken Caldeira, Katsumi Matsumoto,
Guy Munhoven, Alvaro Montenegro, and Kathy Tokos


CO2 released from combustion of fossil fuels equilibrates among the various carbon reservoirs of the atmosphere, the ocean, and the terrestrial biosphere on timescales of a few centuries. However, a sizeable fraction of the CO2 remains in the atmosphere, awaiting a return to the solid earth by much slower weathering processes and deposition of CaCO3 . Common measures of the atmospheric lifetime of CO2 , including the e-folding time scale, dis- regard the long tail. Its neglect in the calculation of global warming po- tentials leads many to underestimate the longevity of anthropogenic global warming. Here, we review the past literature on the atmospheric lifetime of fossil fuel CO2 and its impact on climate,

[ The fate and lifetime of fossil fuel CO2 released to the atmosphere is not inherently scientifically controversial, but the packaging of this information for public consumption is strewn with such confusion that Pieter Tans proposed in print that the entire concept should be banished (Tans et al.
1990). How long is global warming from CO2 going to last, policymakers and the public would like to know. If there is a trade-off possible between emissions of CO2 versus emissions of other greenhouse gases, how shall they be compared? The lifetimes of greenhouse gases are incorporated into the construction of global warming potentials, the time-integrated climate impact of each gas relative to CO 2


There is a strong consensus across models of global carbon cycling, as exemplified by the ones presented here, that the climate perturbations from fossil fuel–CO2 release extend hundreds of thousands of years into the future. This is consistent with sedimentary records from the deep past, in particular a climate event known as the Paleocene-Eocene thermal maximum, which consisted of a relatively sharp increase in atmospheric CO2 and ocean temperature, followed by a recovery, which took perhaps 150,000 years


The gulf between the widespread preconception of a relatively short (hundred-year) lifetime of CO2 on the one hand and the evidence of a much longer climate impact of CO 2 on the other arguably has its origins in semantics. There are rival definitions of a lifetime for anthropogenic CO2 . One is the average amount of time that individual carbon atoms spend in the atmosphere before they are removed, by uptake into the ocean or the terrestrial biosphere. Another is the amount of time it takes until the CO2 concentration in the air recovers substantially toward its original concentration. The difference between the two definitions is that exchange of carbon between the atmosphere and other reservoirs affects the first definition, by removing specific CO2 molecules, but not the second because exchange does not result in net CO2 drawdown. The misinterpretation that has plagued the question of the atmospheric lifetime of CO2 seems to arise from confusion of these two very different definitions

As the ocean is acidified, its ability to hold more CO2 decreases, so that the airborne fraction of a kilogram of CO2 is higher if the water has already absorbed a substantial amount of new CO2.


Nowhere in these model results or in the published literature is there any reason to conclude that the effects of CO2 release will be substantially confined to just a few centuries.
In contrast, generally accepted modern understanding of the global carbon cycle indicates that climate effects of CO2 releases to the atmosphere will persist for tens, if not hundreds, of thousands of years into the future


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