My overall position on global warming is that, as a physicist — I studied physics at Cambridge — I am not one of those who deny that carbon dioxide emissions heat the planet. They do have that effect, although there is less certainty about how much the complex feedback effects that climate models seek to replicate may amplify the comparatively modest effect of increasing  and other greenhouse gas emissions. Nonetheless, in my view it is wise to take measures to prevent and to adapt to global warming, and it is sensible to try to assess the costs and benefits of action and inaction to ensure that we adopt the most cost-effective approach.