Why should I do anything for posterity? What has posterity ever done for me?

Groucho Marx describes one end of a spectrum of opinion. The only obligation we owe to future generations is to sell them assets to pay our pensions. Sir Nicholas Stern’s climate change report takes an opposite view. Governments must value the welfare of all present and future citizens equally and give no special preference to current voters. The issue at the climate change summit in Bali, of how governments should balance the claims of present and future generations, is fundamental to all discussion.