Environmental context. The idea that gases produced by plankton living in the oceans can affect cloudiness and regulate climate was given prominence by the promulgation more than 20 years ago by Charlson, Lovelock, Andreae and Warren of the CLAW hypothesis. In the intervening period it has been difficult to prove or disprove the idea, although much research has flowed from its enunciation. Perhaps its lasting legacy is in the way we view the planet and how research is conducted to try to understand how it operates.