James E. Hansen is a charter member of SCGI and is widely considered to be the leading voice in the field of climate change. After 46 years in government service, Hansen stepped down from his position as director (for 31 years) of NASA's Goddard Institute for Space Studies in 2013. Jim has also served as an adjunct professor in the Department of Earth and Environmental Sciences at Columbia University. He continues his prolific research and writing on the topic of climate change and proposals for dealing with the problem effectively.

After graduate school, Hansen continued his work with radiative transfer models and attempting to understand the Venusian atmosphere. This naturally led to the same computer codes being used to understand the Earth's atmosphere. He used these codes to study the effects that aerosols and trace gases have on the climate. Hansen has also contributed to the further understanding of the Earth's climate through the development and use of global climate models.

Hansen is best known for his research in the field of climatology, his testimony on climate change to congressional committees in 1988 that helped raise broad awareness of global warming, and his advocacy of action to limit the impacts of climate change.