Professor Mendelsohn has concentrated his research on valuing the environment. His dissertation included an integrated assessment model of air pollution that could measure the damages of emissions. This work has been extended in recent years to greenhouse gases, where he has been trying to measure the impacts of climate change. Recently, he has returned to studying air pollution in the hope of measuring the marginal damages of emissions across the country. He has also worked on valuing natural ecosystems, from valuing nontimber forest products and ecotourism in tropical rainforests, to coral reefs in the Caribbean and Australia, to measuring recreation in the Pacific Northwest and Alaska.