This chapter sets the scene for future chapters covering a range of low carbon technologies from renewables through to nuclear. It reviews how the evidence base for climate change is building up, what the impacts of climate change might be, and how we are beginning to explore the policies and measures which will be needed to make the transition to a low carbon economy. The year 2005 will go down in history as the beginnings of a broad, politically backed consensus that man’s activity is influencing our climate. In February 2005, the Kyoto Protocol came into force—binding over 170 countries in action to reduce carbon dioxide emissions, accepted by most informed commentators to be the principal cause of anthropogenically forced climate change. In the same year, the G8 group of countries at Gleneagles, Scotland, considered climate change as a key agenda item. Significantly, it set up a forum for discussion with other countries and the emerging economies. The forum, known as the ‘Dialogue on Climate Change, Clean Energy and Sustainable Development’ met for the first time in November 2005. However, the value of the Kyoto protocol is not universally acknowledged. Some argue that although the science underpinning the existence of climate change and the link with carbon dioxide emissions has become unequivocal, the Kyoto protocol is not appropriate for them. A group of these countries, including the US, China, and India (huge emitters of carbon dioxide in their own right) has agreed the need to tackle climate change. Their approach is to promote clean technology development initiatives; though how exactly that partnership will evolve and deliver new low carbon technologies is not, at the time of writing, clear. Nevertheless, whether via the formalized Kyoto Protocol with carbon dioxide emission reduction targets or via other initiatives, a start has been made on the long, uncertain road to a low carbon world. Slowly, but surely, global action on climate change is gathering momentum. The term ‘greenhouse effect’ was first coined by the French mathematician Jean Baptiste Joseph Fourier in 1827. It enables and sustains a broad balance between solar radiation received and Earth’ s radiation emitted or reflected.