Reducing Greenhouse Gases: The Problem

In the previous post, I looked at the prospects for helping combat global warming by decreasing the solar input to the planet, mainly by reflecting light back to space. The basic problem is the size of the planet: to reduce solar input by 1% you have to totally reflect one per cent of the incoming radiation, which involved ideal reflectors of area somewhat greater than 4 x 10^11 square meters.

Superficially, option two, which is to increase heat output, is easier. All you have to do is to reduce the amount of greenhouse gases in the atmosphere. However, that is something of a problem because we are adding almost 9 billion tonne of carbon as greenhouse gases per year. So, to improve the current situation we have to devise a means of taking out more than 9 Gt of carbon, or over 33 billion tonne of carbon dioxide per annum. Worse, much of the carbon is in the form of methane, which is a much worse greenhouse gas, so a target of 50 billion tonne per annum of carbon dioxide is probably a minimal “hold the current state”. Again, the size of the problem is basically the problem.

Carbon dioxide is naturally removed from the atmosphere by weathering certain rocks. To oversimplify, silicates come in two main classes: granitic and basaltic. The granitic rocks have a much lower density than the basaltic, so they tend to float, and our continents are largely granitic, which, having a large fraction of their composition as aluminosilicates, and since aluminium does not form a stable carbonate, these rocks weather mainly to clays and not carbonates. Thus the main rocks of our continents are not going to help.

The basaltic rocks mainly comprise olivines or pyroxyenes, which are two families of iron/magnesium silicates, the former being nominally “salts” of silicic acid, and the latter salts of chains of polysilicic acid. These will weather to form silica and carbonates of their metals, but at varying rates. One of the proposals is to crush peridotite, one of the fastest to weather, into dust and incorporate it into soils. Powdering it increases surface area, thus increasing the rate of reaction because the reaction is limited to where the carbonic acid in water can get at something to react. It will still be slow, and the energy to crush the rock has to come from somewhere, and might be better used to substitute for the worst other means of producing energy. Another problem is that while peridotite is one of the most common rocks on the planet, that is because it is essentially an upper mantle rock, with only odd visits to the surface. Reacting the gaseous carbon dioxide with basalt is nature’s way of taking it from the atmosphere, but with all the basalt on the planetary surface, it will take centuries to remove the excess there now. This is not going work, although it would make sense to bury carbon dioxide if it were already isolated, but preferably into some basaltic zone.

A better way of removing carbon dioxide is to grow more forests, and in particular to permit the equatorial rain forests to regenerate. A further alternative is to grow massive amounts of algae, which would require ocean fertilization. Some marine algae are extremely rapid growing plants (with a microscope you can watch continuous cell division!). For macroalgae, in the 1970s the US Navy showed how such algae could be grown in open ocean water (as opposed to near coastlines) by growing on rafts and fertilizing with bottom water raised by wave power. The experiment succeeded until a rather unfortunate storm wrecked things, but that, to me is a design and engineering problem that could be solved. In short, the technology for growing plants is more or less available.

The algae could then be used to make synthetic fuels, and while that would merely cycle carbon dioxide, it is better than producing more. We could also bury carbon, as any such processing makes some carbon deposited as char. The growing of algae has one further possible advantage; it takes energy entering the oceans and stores it as chemical energy rather than as heat, and it also emits mercaptans, which should make more clouds after absorbing more ultraviolet light.

To be clear, neither of these will solve the problem, but growing plants will at least contribute to a solution.

So, why don’t we? Quite simply, economics. There are two main problems: the tragedy of the commons, and politicians. The first problem is that unless everyone contributes, the problem cannot be solved, but some, of course, will not mind climate change, or, alternatively, decide nothing will affect them, so why should they pay to fix it? Unfortunately, the expense is so great. This is part of why I favour the algal response. The growing of such algae will also support greater fish life, and hence improve the food supplies, and can be used to make liquid fuels, provided the right technology is used, and there is some chance it may increase cloud cover. By addressing three problems, two of which have money-making prospects as well, makes it more likely it would be successful. At first, of course, such algae could be grown near the current coastlines, and we know how to do that.

Politicians are a more intractable problem. An example: in New Zealand politicians were determined that an emissions trading scheme would be its response. Some New Zealanders began planting trees to get credits, but then Ukraine and Russia produced mountains of such paper credits, there price crashed, and while the current trees might be absorbing carbon dioxide, nobody is in a rush to plant more. If you have travelled the world, you will see vast area where forests have been removed and nothing done with the resultant land. Forests could be regrown, especially tropical ones. The problem then is, who pays for them? Why should Brazil, say, spend a lot of money to plant forests to benefit everyone else? It is politics and governance again.