William Lee Steffen (25 June 1947 – 29 January 2023) was an American-born Australian chemist. He was the executive director of the Australian National University (ANU) Climate Change Institute and a member of the Australian Climate Commission until its dissolution in September 2013. From 1998 to 2004, he was the executive director of the International Geosphere-Biosphere Programme, a coordinating body of national environmental change organisations based in Stockholm. Steffen was one of the founding climate councillors of the Climate Council, with whom he frequently co-authored reports, and spoke in the media on issues relating to climate change and renewable energy.
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