I am a professor at Northern Arizona University. My training is in atmospheric science, ecology and public policy. I currently research topics in carbon cycle science, climate science, and climate science policy.

My recent projects involve simulation of the global carbon cycle using the inverse approach, quantifying fossil fuel CO2 from the building to global scale (the "Hestia", "Vulcan" and "FFDAS" projects), the relationships between US energy demand/supply and climate change, the linkages between terrestrial carbon exchange and climate variability, and the impacts of deforestation on climate. I also have worked extensively on climate policy and have been involved, for over 25 years, with the United Nations Climate Change Framework Convention and the Kyoto Protocol. In addition to carbon cycle science and policy, I have worked on stratospheric ozone depletion, radionuclide dose assessment, energy systems modeling, and climate-economic modeling.