In 1822 Fourier presented his work on heat flow in Théorie analytique de la chaleur (The Analytic Theory of heat), in which he based his reasoning on Newton's law of cooling, namely, that the flow of heat between two adjacent molecules is proportional to the extremely small difference of their temperatures. A significant contribution was Fourier's proposal of his partial differential equation for conductive diffusion of heat. This equation is now taught to every student of mathematical physics.
In his senior year at Harvard University, he took a class with oceanographer and global warming theorist Roger Revelle, who sparked Gore's interest in global warming and other environmental issues. After joining the U.S. House of Representatives, Gore held the first congressional hearings on the climate change, and co-sponsor[ed] hearings on toxic waste and global warming. Gore was known as one of the Atari Democrats, later called the "Democrats' Greens: politicians who see issues like clean air, clean water and global warming as the key to future victories for their party.
After graduate school, Hansen continued his work with radiative transfer models, attempting to understand the Venusian atmosphere. Later he applied and refined these models to understand the Earth's atmosphere, in particular, the effects that aerosols and trace gases have on Earth's climate. Hansen's development and use of global climate models has contributed to the further understanding of the Earth's climate.
Hansen has stated that one of his research interests is radiative transfer in planetary atmospheres, especially the interpretation of remote sensing of the Earth's atmosphere and surface from satellites. Because of the ability of satellites to monitor the entire globe, they may be one of the most effective ways to monitor and study global change. His other interests include the development of global circulation models to help understand the observed climate trends, and diagnosing human impacts on climate.