In a recent edition of Nature (593, pp191-4) it was argued that to combat global warming, removing carbon from the atmosphere, which is often the main focus, should instead be reviewed in light of how to lower global temperatures. They note that the goal of reducing warming from pre-industrial times to two Centigrade degrees cannot be met solely through cuts to emissions so carbon dioxide needs to be removed from the atmosphere. The rest of the article more or less focused on how nature could contribute to that, which was a little disappointing bearing in mind they had made the point that this was not the main objective. Anyway, they went on to claim nature-based solutions could lower the temperature by a total of 0.4 degrees by 2100. Then came the caveats. If plants are to absorb carbon dioxide, they become less effective if the temperatures rise too high for them.
Some statistics: 70% of Earth’s land surface has been modified by humanity; since 1960 we have modified 20% of it. Since 1960 changes include (in million square kilometers): urban area +0.26; cropland +1.0; pasture +0.9; forestry -0.8.
The proposal involves three routes. The first is to protect current ecosystems, which includes stopping deforestation. This is obvious, but the current politicians, such as in Brazil, suggest this receives the comment, “Good luck with that one.” This might be achieved in some Western countries, but then again they have largely cut their forests down already. If we are going to rely on this we have a problem.
The second is to restore ecosystems so they can absorb more carbon. Restoration of forest cover is an obvious place to start. However, they claim plantation forests do not usually give the same benefits as natural forest. The natural forest has very dense undergrowth. Unless there are animals to eat that you may end up generating fuel to start forest fires, which wipe out all progress. Wetlands are particularly desirable because they are great at storing carbon, and once underway, they act rather quickly. However, again this is a problem. Wetlands, once cleared and drained are somewhat difficult to restore because the land tends to have been altered in ways to avoid the land reverting, so besides stopping current use, the alterations have to be removed.
Notwithstanding the difficulties, there is also a strong reason to create reed beds that also grow algae. The reason is they also take up nitrogen and phosphate in water. Taking up ammoniacal wastes is very important because if part of the nitrogen waste is oxidized, or nitrates have been used as fertilizer, ammonium nitrate will decompose to form nitrous oxide, which is a further greenhouse gas that is particularly difficult because it absorbs in quite a different part of the infrared spectrum, and it has no simple decay route or anything that will absorb it. Consequently, what we put in the air could be there for some time.
The third is to improve land management, for timber, crops and grazing, Thus growing a forest on the borders of a stream should add carbon storage, but also reduce flooding and enhance fish life. An important point is that slowing runoff also helps prevent soil loss. All of this is obvious, except, it seems, to officials. In Chile, the government apparently gave out subsidies for pine and eucalyptus planting that led to 1.3 million hectares being planted. What actually happened was that the land so planted had previously been occupied with original forest and it is estimated that the overall effect was to emit 0.05 million t of stored carbon rather than sequester the 5.6 million t claimed. A particular piece of “politically correct” stupidity occurred here. The Department of Conservation, being green inclined, sent an electric car for its people to drive around Stewart Island, the small southern island of New Zealand. It has too small a population to warrant an electric cable to connect it to the national grid, so all the electricity there is generated by burning diesel!
The paper claims it is possible to remove 10 billion tonne of CO2 fairly quickly, and 20 billion tonne by 2055. However, my feeling is that is a little like dreaming because I assume it requires stopping the Amazon and similar burnoffs. On the other hand, even if it does not work out exactly right, it still has benefits. Stopping flooding and erosion while having a more pleasant environment and better farming practices might not save the planet, but it might make your local bit of planet better to live in.