His dissertation involved development and application of an early global climate model to analyze the plausibility of then current hypotheses for the causes of ice age cycling.
From 1968 to 1993, MacCracken’s research at the Lawrence Livermore National Laboratory focused on development and application of numerical models to the study of climate change (including study of the potential climatic effects of greenhouse gases, volcanic aerosols, land-cover change, nuclear war, and factors affecting air quality (including photochemical pollution) in the San Francisco Bay Area.
Project director (1976–1979) of the United States Department of Energy’s Multistate Atmospheric Power Production Pollution Study, which focused on acid precipitation in the northeastern US, and was a program adviser (1979–93) for various components of DOE’s Carbon Dioxide Research Program, including serving as lead editor of two volumes of DOE’s 1985 assessments on climate change.
From 2004 to 202007 he served on a scientific expert group convened by Sigma Xi and the UN Foundation at the request of the UN Commission on Sustainable Development to suggest the best measures for mitigating and adapting to global climate change.
He has also prepared several declarations relating to climate change, one of which was cited favorably by Justice Stevens in his majority opinion in the April 2007 decision by the US Supreme Court in the case of Massachusetts et al. versus the United States Environmental Protection Agency (EPA).