On the international scene, it is often difficult for nations to make decisions when more than one of them is involved, but occasionally an issue comes up where it is difficult to even know how to make the decision. Climate change is one of those issues. Leaving aside some recidivists, the mechanism of greenhouse forcing is now reasonably clearly known, and accepted by the scientific community, and, judging by the recent marches, by a reasonable fraction of the public. Less well accepted is what is essentially hysteresis, which means that what happens depends on what has happened before. Almost certainly, we are not currently in a climatic equilibrium (if we ever were). Another point that many seem to have trouble with is that if there is a net heating, or positive power input, it does not follow that temperatures will increase at selected points. The obvious example is that heat going into the polar regions and melting ice does not raise the temperature. But even more significant, if some areas are getting hotter, and the poles stay the same, we have a greater temperature difference, which permits a stronger heat engine (storms) to develop. Stronger cold winds flowing from the poles will cool some regions, even if, overall, the planet is heating.
Our current problem is that with 400 ppm of CO2 in the atmosphere, the additional heat in the oceans are transferring warmer water to the ice sheets, thus melting glacial ice in Greenland and the Antarctic. Suppose we stopped burning fossil fuels tomorrow, the rate of melting would continue unabated for quite some time, first because the additional heat in the oceans at the equator still has to have sufficient time to get to the ice. Further, the oceans will continue to absorb the heat because the atmosphere will continue to have its 400 ppm of CO2, together with other gases such as CH4, N2O, and a number of industrially made gases. If the ice sheets melt, there will be a serious rise in sea-levels. Countries like Bangla Desh will lose half their land, some Pacific Islands will be uninhabitable. So, what should we do?
The current political thinking seems to be, nothing, besides reduce CO2 emissions. However, reducing emissions merely slows the development of the problem; it does not reduce it, because of what is already there. Worse, India has announced it will build a lot of new coal-fired power stations, on the basis that it should have its turn to burn coal. There is an even worse problem: the acidification of seawater due to the CO2 it has absorbed is bringing it close to the level where aragonite does not precipitate out. A very large number of shellfish, at least in their juvenile stages, depend on aragonite to make their protective shells. Accordingly, we have two problems: how to stop global warming, and how to stop ocean acidification? Each of these can be addressed by geoengineering, although the ocean acidification has the fewest options.
There was an article in Science (vol 347, p1293) that raised the question, what would happen if some country decided to burn a lot of sulphur, which would help form clouds and reduce the albedo? The reason the country might have decided to do this could be because it had had a series of bad harvests, and it blamed climate change. The problem, of course, might be that now some other country might have its harvests fail (and in this case, ocean acidification would hardly improve.) The problem is that anyone who does something will hardly know what their actions will do elsewhere, and even if they can guess, who is responsible for what happens? What is needed is more information, but how do we get that information? How do you carry out an experiment that will provide data on a global scale without the possibility of influencing the globe? And who will support the experiment? Who will regulate what is done, and on what basis? One unfortunate aspect is that politicians will put themselves in the deciding role, they will not understand the problem, and they will act solely in the interests of their own country. Not an attractive prospect for our grandchildren.
