Month: June 2008

Those wanting to reduce their contribution to climate change are generally presented with two options: cut back on your own emissions or pay someone else to do so. The first requires sacrifice and/or time and/or capital. You can give up flying, meat, and air conditioning; you can take trains instead of planes; you can invest in solar panels and ground source heat pumps. The second set of options is arguably more practically challenging and morally problematic. It is harder to verify that someone else has actually cut emissions, and done so in response to your payment rather than any other incentive. There are also those who think it unacceptable to buy your way out of taking action yourself.

There is, at least theoretically, a third option. Suppose I buy an area of land in British Columbia. The place is ideal for growing trees and the trees on the lot grow each year, absorbing carbon from the air in order to do so. As a result, my little forest is a net carbon sink. The danger, of course, is that the carbon will be re-released. Someone might cut down my forest. My forest might dry out or burn down (possibly because of climate change). Then, I will have accomplished little of value, given that carbon dioxide has a long atmospheric life. For most intents and purposes, it may as well never have been absorbed.

What I need to do is ensure the carbon doesn’t go anywhere. Here are some options I have come up with:

1. Cut down trees at the growth rate (if one matures per month, cut one per month). This ensures that the forest will always be absorbing the same amount of carbon per unit time. Then, encase the lumber in something durable and air tight – keeping the carbon inside sequestered indefinitely. Then, either use the wood as building material or simply bury it.
2. Cut down trees as described above and bury them somewhere they are relatively unlikely to decompose: such as a peat bog or the Arctic tundra.
3. Cut down trees as described, chop them into chips, burn the chips for energy, capture and sequester the carbon dioxide underground. This approach has some variants: (a) seperate oxygen from air and burn the chips in that to produce gaseous outputs that are mostly CO2 or (b) convert the biomass chips into syngas (hydrogen and carbon monoxide) before combustion.

Of course, there are issues with all of these:

1. Is it possible to shrink wrap wood in a way that will keep the carbon inside indefinitely? How many carbon emissions would be associated with making the shrink wrapping material?
2. The Arctic tundra is melting, threatening massive carbon releases. Global temperature rise could do the same to peat bogs.
3. This may require tens or hundreds of millions of dollars worth of capital and skilled labour, depending on how much all the equipment costs. Nobody could do this alone, though it may be possible to do at a commercial scale, partly in exchange for payments from those having their emissions offset.

None of these are great options, but they do offer at least the logical possibility of actually, literally offsetting one’s carbon emissions. For those with aspirations for world travel, but also serious ethical concerns about climate change, such options may prove the only choice.

One of the larger unknowns when it comes to the impact of human carbon dioxide emissions is the degree to which living things will be harmed by more acidic oceans. This is occurring because water with more CO2 dissolved in it is more acidic. There are concerns that overly acidic sea water might compromise the ability of organisms with shells made of calcium carbonate to build and maintain their bodies. Other affects on marine ecosystems are anticipated, though it is challenging to assess what their magnitude will be and when they will occur.

Scientists recently completed a study of a place where such effects are occurring naturally due to carbon dioxide venting from the sea floor:

Around the vents, [pH] fell as low as 7.4 in some places. But even at 7.8 to 7.9, the number of species present was 30% down compared with neighbouring areas.

Coral was absent, and species of algae that use calcium carbonate were displaced in favour of species that do not use it.

Snails were seen with their shells dissolving. There were no snails at all in zones with a pH of 7.4.

Meanwhile, seagrasses thrived, perhaps because they benefit from the extra carbon in the water.

The latest IPCC estimate is that global pH will fall from 8.1 today to about 7.8 by 2100. Greater than expected CO2 emissions would cause a larger change. Coral reefs are especially likely to suffer.

Oceanic acidification is the inevitable result of adding CO2 to the atmosphere, but it not otherwise causally connected to climate change. It does add a complication to any plan that seeks to reduce global temperature change through a means other than reducing CO2 emissions; even if more energy could somehow be reflected or dissipated into space, the marine consequences of acidic oceans would endure.

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.