There is increasing evidence that climate change is occurring, and the anthropogenic contribution to such change is being clarified (IPCC, 2007a, b, c, d). While most experts in the field accept this proposition, a diminishing number of vocal sceptics are to be found in academia, in political circles and in the media. This chapter considers the evidence for climate change. Chapters 19 and 20 examine the microevolutionary consequences of such changes, and the implications for conservation.

The greenhouse effect and climate change

Solar energy is received on Earth from the Sun. Some of this energy is reflected back from clouds and the Earth's surface, but some is trapped by the so-called greenhouse gases (water vapour, carbon dioxide, carbon monoxide, methane and nitrous oxide) resulting in the warming of the planet. As we shall see, there is mounting evidence that anthropogenic activities are increasing the levels of these gases in the atmosphere resulting in global warming.

This account draws on the recent Fourth Intergovernmental Panel on Climate Change Assessment Report (IPCC, 2007a) on the physical sciences basis for accessing climate change. It has been prepared by over 1,200 expert authors, and reviewers from 40 countries (Giles, 2007). At the time of writing only the Summaries for Policy Makers are available.