Tim began working in the Carbon Dioxide Group at Scripps in 1983, measuring dissolved inorganic carbon (DIC) and Alkalinity in seawater. He earned his Ph.D. under C.D. Keeling in 1998, and then began a postdoc with Ralph Keeling establishing a measurement site for atmospheric O₂/N₂ and CO₂ in Trinidad CA. His specialties include measurements of O₂/N₂ and CO₂ ratio, CO₂, and other greenhouse gases in air, and the inorganic carbon chemistry of seawater. He also installs and maintains instruments in Hawaii, helping to document the rising levels of CO₂ in a time series popularly referred to as the "Keeling Curve".