> What I find interesting is the implicit assumption that only nature can
> take carbon out of the air, apparently even over hundreds or thousands
> of years, once humanity has stopped emitting carbon.
Only nature will take CO2 out of the air if we do not act.
> Clearly, that is not so. We can take carbon from biomass for example
> and bury it.
Buried biomass turns into methane which escapes to the surface as an even
more potent greenhouse gas than carbon dioxide.
What we can do is sink wooden logs in water - sea or lakes, and so begin its
metamorphism into coal.
> In fact, given sufficient energy, we can take carbon directly from air
> and bury it.
We would have to burn more carbon in the fossil fuels used to provide the
energy than we could remove from the air. Nature's methos of photosynthesis
is far more practical. However, plans have already been made to trap the
high concentrations of carbon dioxide from fossil fuel burning power
stations, which is effective, but if the CO2 buried under pressure were to
escape it would suffocate those living near the burial site.
> I think this should feature in scenarios for future carbon levels, as
> should in some form the possibility of less energy intensive ways of
> taking out carbon (primarily I am thinking of techniques to enhance the
> weathering of rocks).
How do you propose to do speed up a geological process that acts on a
timescale of millions of years?
I am sure that all practical solutions to the problem will be discussed in
the Mitigation section of the latests IPCC report due out early next year.
Cheers, Alastair.
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