Nearly 20 years ago, in an article in the New York Review of Books, Freeman Dyson pointed out that the U.S. could eliminate excess carbon emissions by increasing the topsoil by three-eighths of an inch.
I happen to have the aforementioned article. Here is an excerpt:
Post bumpedRoughly speaking, half of the contiguous United States, not including Alaska and Hawaii, consists of mountains and deserts and parking lots and highways and buildings, and the other half is covered with plants and topsoil. Just to see how important an unmeasurable increase of topsoil may be, let us imagine that the increased root-to-shoot ratio of plants might cause an average net increase of topsoil biomass of one tenth of an inch per year over half the area of the contiguous United States. A simple calculation shows that the amount of carbon transferred from the atmosphere to the topsoil would be five billion tons per year. This amount is considerably more than the measured four-billion-ton annual increase of carbon in carbon dioxide in the atmosphere. So the increase of carbon dioxide in the atmosphere over the entire earth could be canceled out by an increase of topsoil biomass of a tenth of an inch per year over half of the contiguous United States.
A tenth-of-an-inch-per-year increase of topsoil would be exceedingly difficult to measure. At present we do not even know whether the topsoil of the United States is increasing or decreasing. Over the rest of the world, because of large-scale deforestation and erosion, the topsoil reservoir is probably decreasing. We do not know whether intelligent land management could ensure a growth of the topsoil reservoir by four billion tons of carbon per year, the amount needed to stop the increase of carbon dioxide in the atmosphere. All that we can say for certain is that this is a theoretical possibility and ought to be seriously explored.
Interesting idea, worth some thought. As it happens, my neighbor received a truckload of topsoil today, which he plans to work into his flower beds. But, in case any of your readers are moved to praise him, this is not what Dyson is writing about. My friend simply paid to have already existent topsoil moved from one place to another, which will have no net effect on CO2 sequestration.
ReplyDeleteThe same neighbor, along with millions of others, dutifully rakes his fallen leaves every November, places them in plastic bags, and pays for them to be trucked to a landfill, where they will sit for decades sealed off from the microbes which could decompose them into topsoil. Instead, he could simply use a mulching mower weekly during the fall, shredding the leaves into tiny pieces, and collecting them into large piles to decompose over the next few years. I've been doing this for twenty years, basically running a topsoil factory which supplies me with all that I need.
The important point to emphasize is that any CO2 sequestration scheme involving topsoil must be driven by a net increase in decomposed plant biomass, which in turn must be driven by a net increase in plant biomass. And a net increase in plant biomass could arise from greater primary productivity in areas currently covered with vegetation, by an increase in landmass covered by vegetation, or both. For reasons I've explained here before, increasing primary productivity per acre in wild lands is simply not possible, so that leaves us with the option of increasing the percentage of landmass covered by vegetation. Unfortunately, we have been moving in the opposite direction for decades. So, even though Dyson's idea is a theoretical possibility, like many of his ideas it's a practical impossibility.
Part 2 of my comment will appear tomorrow, when I look at the other necessary component of topsoil formation: the ecosystem of microbes and insects that actually do the work of decomposing plant biomass into topsoil. There may be some opportunity for marginal benefit by increasing the rate of decomposition of plant biomass, even if we're unable to increase the amount available for decomposition.
ReplyDeleteIncreased plant biomass can lead to increased topsoil biomass only if the soil ecosystem is healthy. This ecosystem includes hundreds of species of insects, crustaceans, annelids, bacteria, and fungi which work together to decompose plant detritus into topsoil. Though I can't see any practical way to increase soil health in wild lands, there is one category of land use where improvements can be made: cropland.
ReplyDeleteEighteen percent of the surface area of the U.S. is devoted to growing annual crops. Cropland soil is largely barren of the organisms required to form new topsoil, due to the use of fungicides and insecticides on 99% of this land. The chemicals kill pests, but also harm many beneficial soil organisms. One obvious solution is an increase in organic farmland beyond the 1% it currently represents. This would most likely increase food prices due to lower productivity, but the reality is that lowering the levels of CO2 in the atmosphere is going to affect consumers one way or another, whether through higher food costs, higher vehicle costs, or higher housing costs.
Another possible solution is the use of modern genetic techniques to increase innate plant resistance to pathogens and destructive insects, allowing a reduction in the use of pesticides. The much-derided GMO technology is one such approach, but other less well-known techniques like mutation breeding, gene introgression from wild relatives, and marker-assisted selection also show much promise.