Legislating for the present on the basis of predictions for the future can never be other than a dicey business. The suggestion by a British member of parliament in the nineteenth century that London would be waste-high in horse excrement by the 1950s could have been seen as a call for crippling taxes on Hansom cabs, pushing cabbies out of trade while still leaving us choking on exhaust fumes. So should we now be legislating against those exhaust fumes, in fear that by the end of the next century the world will be a flood- and storm-prone hothouse?
This was one of the key issues highlighted by the Kyoto convention on climate change in 1997. It is all very well to set targets for emissions reductions on the basis of climate models projected over the next century (and then in all probability to fall short of attaining them anyway), but what of the costs of fierce constraints to today's populations, particularly those who live within fragile economies?
Yet clearly we have to do something. There seems to be no serious doubt now that global warming, induced by emission of greenhouse gases through human activity, is upon us. The global average temperature has risen by around half a degree Celsius during the twentieth century, and is predicted to increase by a further 1.0–3.5 °C by 2100. Over the same periods, the seas have risen by 10–25 cm and we can expect almost a metre more at the upper limit. Storms and drought may or may not get more common, but their distribution will probably alter. Massive famine and flooding cannot be ruled out.
As it happens, the Kyoto targets may make very little impact on all of this, but the basic question remains: how can we plan for social change on timescales over which forecasts of enabling technologies become unreliable? One approach that has been advocated is to formulate policy based on assessments of human and social impacts rather than in terms of national emissions reduction targets — something that is harder to quantify but closer to people's concerns. Emissions are not the whole story; what about economic efforts to make societies vulnerable to climate change less so? And how far do political and industrial structures need re-engineering to make actual attainment of objectives realistic?
Climate modellers, meanwhile, are trying to incorporate some element of the social and economic contexts into their forecasts. They grapple with the question of whether it is better, given the uncertainties, to brake hard on emissions now, do nothing until later on the assumption that we will then be much more technologically capable of it (owing to enhanced energy efficiency and so forth), or something in between. Inevitably, such modelling is painfully contentious and strongly influenced by the assumptions that go into it. We are juggling with the unknown; and in the face of massive inertia and sharp political lobbying, that is a precarious occupation.