So what is it we know about human induced global warming? The most important emission is carbon dioxide, the atmospheric content of which has varied between 0.15 and 0.3 per cent over the past half million years. It is only harmful to humans or other animals at concentrations of over 10 per cent and life actually evolved when the atmospheric content was about 7 per cent A doubling of carbon dioxide content to about 0.6 per cent is likely over the coming century. Almost all scientists agree that the main direct effect of this is to increase average global temperatures by slightly over 1°C (beyond a doubling of its share, further carbon dioxide increases have a negligible climate effect) Most models estimate that this is compounded by feedbacks bringing 2-4°C temperature increases. But those feedback effects are unproven and their impact may even be negative. This is at the heart of the differences between ‘warmists’ and ‘deniers’ Higher temperatures stemming from carbon dioxide emissions are likely to compound what most scientists speculate is a trend recovery from the cooler climate experienced during the ‘Little Ice Age’ (which ended a century and a half ago) Each summer brings ‘the hottest day ever’ claims for some area. Sometimes we hear ‘the coldest day ever’ claims. And many cite these occurrences and well publicised storms as proof that ‘climate change’ (the new euphemism for ‘global warming’) is taking place. But these extreme weather events turn out to be unexceptional.