Nigel Sizer serves as the executive director of the Preventing Pandemics at the Source initiative with Dalberg Catalyst. Concurrently, he is also, Chief Global Alliances Officer with the Rainforest Alliance.  He served for two years as president of Rainforest Alliance until January 2018. He helped lead the successful merger with the leading Dutch-based non-profit UTZ and following the merger he served as Chief Program officer.

Previously, as global director of the Forests Program at the World Resources Institute, Sizer led a hundred-person team across Africa, Asia, and Latin America and launched path-breaking partnerships including the award-winning Global Forest Watch and the Global Restoration Initiative.Sizer also served as vice president for Asia-Pacific with Rare, where he developed grassroots efforts to link impoverished communities in Indonesia to global carbon markets and pioneered community-based fisheries and marine protected areas efforts. In 2008, he served as lead advisor on climate change and energy issues in Asia to former US President Bill Clinton and the Clinton Global Initiative. He has also worked with the United Nations Environment Program (UNEP) in Nairobi and established The Nature Conservancy’s Asia-Pacific Forest Program. He also founded and co-chaired The Forests Dialogue, which recently celebrated 20 years of progress, and helped establish and lead the Asia Forest Partnership.

A globally recognized authority on forests, ecology, climate change and development policy, Sizer holds Bachelors, Masters, and Doctoral degrees in natural sciences and tropical forest ecology from the University of Cambridge. He has lived and worked in Brazil, Kenya, and spent ten years in Indonesia. He has served on numerous boards and advisory groups including Natural State, Tree Global, the Tropical Forest Alliance, the Rainforest Foundation, the Amazon Alliance, the Global Forest Foundation, and the Andean Center for Sustainable Development. He has received numerous awards including the Henry Arnold Conservation Fellowship from the Mulago Foundation and the United Nations Secretary General’s Big Data Challenge prize.