Attributing cause and effect

Abstract

The climate is changing, and so are aspects of the world's physical and biological systems. It is no easy matter to link cause and effect — the latest attack on the problem brings the power of meta-analysis to bear. Many natural biological and physical systems are undergoing changes consistent with a gradual rise in temperature. Such changes have occurred on all continents and in most oceans since at least 1970. An Article in this issue is the first to formally link the observed changes to human-induced climate change. The study is a meta-analysis that uses a larger database than the recent IPCC report, and it takes account of land-use change and other complications. The authors conclude that anthropogenic climate change is affecting physical and biological systems globally. But as Francis Zwiers and Gabriele Hegerl point out in News & Views, this proof based on the principle of joint attribution stops short of the statistical certainty that would be provided by 'end-to-end' models linking human activity directly to the observed changes, rather than via effects on the climate system.