Global Warming Is True - Isn't It?

Abstract

Scientists are now sure that global warming is a real phenomenon. No ifs or buts, this is a definite statement. It’s true. Three of the past 8 years have been the hottest since at least the Middle Ages. What could be more definite? Three years in the last 500, maybe 600 years and they were all in the last decade. In the past if weather got a kick in the pants it used to be due to volcanic eruption, unusual changes in the sun-spot pattern or the now infamous El Nino behaving oddly. Now it’s us. We keep on burning things, mostly fossil fuels but also forests. This last year has been particularly bad for forest burning. Burning carbon containing material produces carbon dioxide and that is a ‘greenhouse gas’. I know that a few years ago we worried about CFCs and their effect on the ozone layer but that is another story and they no longer seem to be major players in any doomsday drama, today carbon dioxide is at the front of the stage. However, the role of carbon dioxide is not entirely clear. We know that the amount in the atmosphere has increased since the time before the Industrial Revolution. This increase is probably the most believable part of the story because we can measure the levels very accurately and have been able to do so for many years. In the pre-industrial era carbon dioxide levels were around 280 ppm, by the time of the second world war they were still only around 290 ppm but now that figure has increased to around 355 ppm. If and how this increase is responsible for and related to global warming is a difficult problem and there seems to be little consensus between the experts involved in its study. Some will say that the increased level plays a major part in the global warming that we are experiencing. Others will deny that we are experiencing global warming or if we are then the role of carbon dioxide is greatly overstated. So I should restate my opening sentence and say that some scientists are absolutely convinced that the biosphere is hotting up and that carbon dioxide is largely responsible. I am sitting on the fence. The Intergovernmental Panel on Climate Change (IPCC) has said in a report [1] that ‘carbon dioxide has been responsible for over half the enhanced greenhouse effect in the past, and is likely to remain so in the future’. The increase in carbon dioxide levels is continuing and in the future there will be a lot more. How much more depends on the credence you give to the many scenarios that have been proposed so ‘a lot more’ seems to be accurate enough as a description. Of course the problem is compounded by the fact that the relationship between carbon dioxide in the atmosphere and the mean global temperature is not, as I said earlier, a simple one. During the Cretaceous period carbon dioxide levels were in excess of 2,000 ppm and yet temperatures were little different to those today. Arguments about changes taking place in geological time have the advantage that vagueness is to a degree acceptable. A year, a century, or even a millennium are unimportant. The correct order is important; before this but after that and about the same time as are necessary and adequate. Exactly when something occurred is less so. If we go back in the time of the history of the Earth by some 3 billion years we arrive in an era when life had begun but the degree of cellular organisation had not got a long way beyond one. There may have been colonies of cells but such aggregation was probably disorganised. Most importantly for the march of evolution the biosphere was anaerobic. Oxygen, strictly dioxygen, levels were constrained to below 0.001% of the present atmo-