The IPCC does its best to contest this by claiming that warming is bad for food production: in its own words, "negative impacts of climate change on crop yields have been more common than positive impacts". But not only does it fail to acknowledge that the main negative impact on crop yields has been not climate change but climate change policy, as farmland has been turned over to the production of biofuels rather than food crops. It also understates the net benefit for food production from the warming it expects to occur, in two distinct ways.

In the first place, it explicitly takes no account of any future developments in bio-engineering and genetic modification, which are likely to enable farmers to plant drought-resistant crops designed to thrive at warmer temperatures, should these occur. Second, and equally important, it takes no account whatever of another effect of increased atmospheric carbon dioxide, and one which is more certain and better documented than the warming effect. Namely, the stimulus to plant growth: what the scientists call the "fertilisation effect". Over the past 30 years or so, the earth has become observably greener, and this has even affected most parts of the Sahel. It is generally agreed that a major contributor to this has been the growth in atmospheric CO2 from the burning of fossil fuels.

This should not come as a surprise. Biologists have always known that carbon dioxide is essential for plant growth, and of course without plants there would be very little animal life, and no human life, on the planet. The climate alarmists have done their best to obscure this basic scientific truth by insisting on describing carbon emissions as "pollution" — which, whether or not they warm the planet they most certainly are not — and deliberately mislabelling forms of energy which produce these emissions as "dirty".

In the same way, they like to label renewable energy as "clean", seemingly oblivious to the fact that by far the largest source of renewable energy in the world today is biomass, and in particular the burning of dung, which is the major source of indoor pollution in the developing world and is reckoned to cause at least a million deaths a year.

Compared with the likely benefits to both human health and food production from CO2-induced global warming, the possible disadvantages from, say, a slight increase in either the frequency or the intensity of extreme weather events is very small beer. It is, in fact, still uncertain whether there is any impact on extreme weather events as a result of warming (increased carbon emissions, which have certainly occurred, cannot on their own affect the weather: it is only warming which might). The unusual persistence of heavy rainfall over the UK during February, which led to considerable flooding, is believed by the scientists to have been caused by the wayward behaviour of the jetstream; and there is no credible scientific theory that links this behaviour to the fact that the earth's surface is some 0.8ºC warmer than it was 150 years ago.

That has not stopped some climate scientists, such as the publicity-hungry chief scientist at the UK Met Office, Dame Julia Slingo, from telling the media that it is likely that "climate change" (by which they mean warming) is partly to blame. Usually, however, the climate scientists take refuge in the weasel words that any topical extreme weather event, whatever the extreme weather may be, whether the recent UK rainfall or last year's typhoon in the Philippines, "is consistent with what we would expect from climate change".

So what? It is also consistent with the theory that it is a punishment from the Almighty for our sins (the prevailing explanation of extreme weather events throughout most of human history). But that does not mean that there is the slightest truth in it. Indeed, it would be helpful if the climate scientists would tell us what weather pattern would not be consistent with the current climate orthodoxy. If they cannot do so, then we would do well to recall the important insight of Karl Popper — that any theory that is incapable of falsification cannot be considered scientific.