Trained as a chemist at Queen Mary College, London, Bob Watson had no intention of entering the public-policy arena. He researched how halogen atoms, such as chlorine, interact with ozone to form chlorine monoxide radicals. See CV

During a postdoc at the University of California, Berkeley, Watson saw that chemistry had social relevance as he watched mentor Harold Johnston debate with the Nixon administration over the impact of supersonic transport on stratospheric ozone depletion. When chlorofluorocarbons were found to trigger that depletion, Watson's expertise was suddenly in high demand. “Careers are made as much on luck as judgement,” he says.

Joining NASA as a scientist in the Jet Propulsion Lab in Pasadena, Watson left as director of the science division. During his time there, he was asked to direct a national assessment of ozone depletion. Watson cited seven other recent assessments and sought not to duplicate efforts, but build international consensus. “Policy-makers need a single scientific assessment by the world's best scientists,” he says.

His next move was to the White House, into the president's Office of Science and Technology Policy. He continued to lead assessments, co-chairing a working group of the Intergovernmental Panel on Climate Change (IPCC) and the Global Biodiversity Assessment. In 1996, he began a decade at the World Bank, directing its environment department, and then becoming the bank's chief scientist, while also serving as chair of the third IPCC report.

Former World Bank colleague Ian Johnson, now chairman of IdeaCarbon, a UK-based carbon market analysis firm, says Watson was one of the rare scientists who saw science not as outside of public policy, but as integral to it — especially as a driver of development change. “Scientists don't often like to see consensus and compromise, but Bob understands the sometimes painstakingly slow need to listen and share information to reach consensus,” says Johnson.

In his latest move, Watson has accepted three positions: as the chief scientific adviser of the UK Department of Environment, Food and Rural Affairs; as a professor at the University of East Anglia; and as director for strategic development of a unique collaboration of UK academics at the university's Tyndall Centre for Climate Change. Although he has no plans to participate in yet another international assessment, he doesn't dismiss the idea. “My entire career has been a random walk, so one never knows,” he says.