The New York Review of Books recently featured a couple of book reviews by Freeman Dyson. In them, he shares some interesting ideas:
- There is a famous graph showing the fraction of carbon dioxide in the atmosphere as it varies month by month and year by year
- [The graph features] a regular wiggle showing a yearly cycle of growth and decline of carbon dioxide levels. The maximum happens each year in the Northern Hemisphere spring, the minimum in the Northern Hemisphere fall. The difference between maximum and minimum each year is about six parts per million.
- The only plausible explanation of the annual wiggle and its variation with latitude is that it is due to the seasonal growth and decay of annual vegetation, especially deciduous forests, in temperate latitudes north and south.
- When we put together the evidence from the wiggles and the distribution of vegetation over the earth, it turns out that about 8 percent of the carbon dioxide in the atmosphere is absorbed by vegetation and returned to the atmosphere every year. This means that the average lifetime of a molecule of carbon dioxide in the atmosphere, before it is captured by vegetation and afterward released, is about twelve years.
- [I]f we can control what the plants do with the carbon, the fate of the carbon in the atmosphere is in our hands.
- Carbon-eating trees could convert most of the carbon that they absorb from the atmosphere into some chemically stable form and bury it underground. Or they could convert the carbon into liquid fuels and other useful chemicals.
This is, of course, a geoengineering scheme. As such, it is subject to the two major points of opposition: that we don’t know whether it would work, and that it would probably produce unwanted and unpredictable consequences. That being said, it seems less dangerous in the latter regard than schemes to fertilize oceans or fill the air with aerosols. Ideally, these enhanced trees would just behave like a larger number of normal trees.
Genetic modification of plants is likely to play a role in addressing climate change. Food crops are an obvious area where that is true. They may need to be made more resistant to heat, extreme weather, drought, and floods. They may even need to have their photosynthetic pathways altered. If, along the way, we come up with a mechanism for producing trees that eat more carbon, it could make a useful contribution to the overall effort.
We should not, however, forget the third big danger connected to geoengineering: the risk of falling into the complacent belief that technology will bring an answer. Super carbon eating trees are a long-shot – one worth considering, perhaps, but no excuse to keep on burning forests and coal.