Computer models – can we trust them?

I have decided to break into my mini-critique of the school of environmental thought known as Ecological Modernisation (i.e. seeking solve the potential problem of perpetual growth on a finite Planet!) to address the above question. This is because, at the end of yesterday’s post, I referred to the UN’s latest computer-based projections for global human population by 2100AD, which got me thinking… No-one questions whether the people at the UN know where babies come from! They are quite happy to accept that uncertainties in population projections (which range from 6 to 15 billion by 2100AD) are a consequence of uncertainty in trends in education, female emancipation, contraception use, fertility and mortality rates! If so, why will people not accept the same logic when it comes to global climate models? For sure they are complex; but so is the human brain! The effects of atmospheric carbon dioxide (CO2) – even at very low concentrations – are very well understood; and have been for over 100 years. Climate models proved their accuracy in the early 1990’s when they were re-run using data from the Mt Pinatubo eruption and correctly predicted the size and duration of the reduction in global average temperatures it caused. However, they are only this accurate because they take into account all the factors affecting the climate, which include pollution, water vapour, and solar activity; and by a process called sensitivity analysis, it has been proven that they are only accurate when they treat CO2 as the primary driver of change. As Clive Hamilton has recently pointed out, in Requiem for a Species, the wide range of results reported by the probabilistic models now in use, “…is not due to uncertainties about how much warming is associated with a given concentration of greenhouse gases… but to the difficulty in forecasting the… world’s greenhouse gas emissions” (page 6). Therefore, anybody who says models are unreliable or uncertain is just trying to obscure the fact that we are extremely certain about the consequences of burning fossil fuels. The only thing we have yet to decide is how quickly we are going to stop doing it. Killing-off climate change denial is a Herculean task; analogous to trying to kill the multi-headed monster of Greek mythology. Unfortunately, this particular monster is very real, very strong, and very persistent. However, we must hope that — emboldened by the facts that: (1) the current warming is unprecedented in 100’s of millions of years; (2) the frequency of extreme weather events of all kinds (hot, cold, wet and dry) has increased as was predicted; and (3) the Arctic is warming faster than was predicted — climate scientists will now prevail over the defenders of profligate consumption (and the inadvertent enemies of reason); and win over public opinion. Despite the fact that the battle may have already been won in the court of scientific and political opinion (denialists will obviously dispute this), I believe that the public must be won over as well (despite the ever-present problem of issue fatigue), because what the politicians have achieved so far is just not good enough; even they do not seem to be taking the problem seriously enough. However, if their timidity is due to fear of an electoral backlash if they state the problem clearly enough, they need to get over it because this problem is not going to go away; and will only get worse if we delay tackling it.