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Michael Maccracken

May 3, 2013


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Promoting additional forest growth is indeed one approach to limiting the amount of CO2 in the atmosphere. The problem is really one of scale, especially if nothing is done to limit CO2 emissions. To give a sense of this: a. Present emissions of CO2 equal about 10 GtC/yr (or 10 Petagrams (Pg) of C per year), or nearly 40 Gt CO2 per year (or, as the international negotiators say, about 40,000 million metric tons of CO2 per year). Scientists tend to talk in terms of C so we can follow each atom, etc., whereas those doing the negotiations seem to want to deal with large numbers so when a small action is agreed to it still ends up being a pretty large number (or am I too cynical?). b. The amount of carbon (C) in the above ground biosphere over the whole world is currently something like 600 GtC. The amount below ground is roughly double this amount. c. The net seasonal uptake of C by the Northern Hemisphere biosphere each year (and there is relatively little Southern Hemisphere biosphere that changes through the seasons) is about 8-9 GtC. This is derived by multiplying the seasonal variation in the CO2 concentration at Mauna Loa (viewed as representative of the average, well-mixed NH concentration) of about 8-9 ppmv by the volume of the Northern Hemisphere and doing the necessary conversions. d. So, if all of the CO2 emitted from present levels of fossil fuel combustion were taken up each year and stored in the above ground biosphere, we would be doubling the amount of above ground vegetation every 70 years or so. Accounting for some storage below ground--it takes time to build this up--would increase the time, but with increasing emissions, the time would become shorter. e. So, given current emissions levels (and, on average, they are increasing at a few tenths of a GtC/yr each year) the real problem is there is not enough space to do it, and even doing 10% of this amount per year, so 1 GtC/yr would be a lot to be doing. Were the emission levels a tenth of where they are and we needed to have a net zero emissions for a stable climate, reforestation and afforestation (converting areas not now forests to forests) might well be the way to go. f. There is an interesting paper that goes into this idea of afforestation as a potential approach--see for some discussion of the idea. Basically, one would have to have new forests covering the entire Sahara Desert or all of Australia to be taking up enough carbon. The authors suggest using eucalyptus and describe how they could supply enough water using renewable energy and desalination. Quite fascinating. Of course, one the areas are covered with forest, then what? And one problem is that eucalyptus is quite flammable (there was a major fire some years ago in Oakland, California that was fueled in part by eucalyptus that had grown up since the previous fire back in the 1920s or so. So, indeed, reforestation and afforestation have a potential role to play, but are not near the solution.

Johnnie Buttram

May 5, 2013


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Mike, You are absolutely correct to state Geo-Safe (CDR) is not powerful enough to be a solution! To be honest - I knew this when I wrote the proposal. I am always hopeful that if enough good variables become positive factors; these factors may nurture the innovation to give us a solution!

2013geoengineeringjudges 2013geoengineeringjudges

Jul 10, 2013


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Thank you for sharing your ideas and for the work invested to create this proposal. We have considered this proposal carefully, and while it makes very interesting suggestions, as mentioned in comments above and pointed out by you as well, the scheme envisioned cannot have the large impact needed to constitute the major part of a geoengineering solution.