Simon L. Lewis is Chair of Global Change Science at University College London and the University of Leeds. Professor Lewis is a tropical field ecologist who studies global environmental change.

Professor Lewis' major contributions to science have been to understand how the world's tropical forests have been responding to environmental change, including that intact tropical forests have been absorbing globally significant quantities of carbon dioxide over recent decades, slowing climate change. He later revealed that this uptake is now in decline.

Professor Lewis' team recently described and mapped a new ecosystem type to science, the central Congo peatlands, spanning 16.8 million hectares. Subsequently, he uncovered its threshold behaviour, absorbing carbon when the climate is wetter and releasing it when drier – a new feedback in the global carbon cycle.

Professor Lewis' research is highly collaborative, relying on teams of scientists working together with people living in the world’s tropical forests, to gain insights into our changing planet.