A majority of the world’s climate scientists have convinced themselves, and also a lot of laymen, some of whom have political power, that the Earth’s climate is changing; that the change, from humanity’s point of view, is for the worse; and that the cause is human activity, in the form of excessive emissions of greenhouse gases such as carbon dioxide. A minority, though, are sceptical. Some think that recent data suggesting the Earth’s average temperature is rising are explained by natural variations in solar radiation, and that this trend may be coming to an end. Others argue that there is no conclusive evidence that modern temperatures are higher than they used to be.we believe that global warming is a serious threat, and that the world needs to take steps to try to avert it. That is the job of the politicians. But we do not believe that climate change is a certainty. There are no certainties in science. Prevailing theories must be constantly tested against evidence, and more evidence collected, and the theories tested again. That is the job of the scientists.