As a scientist at Exxon, Cohen spent the 1980s contributing to the company's climate research. During that time, he once described the predicted future impacts of climate change as "catastrophic" for most people on Earth. Cohen worked at Exxon for approximately 25 years, retiring in 2003 as a manger of strategic planning. After leaving the company, he became an outspoken climate denier. He helped lead the push for the American Physical Society to weaken its stance on the issue. In an article published in 2008, Cohen wrote: "...at the time of my retirement I was well convinced, as were most technically trained people, that the Intergovernmental Panel on Climate Change's case for Anthropogenic Global Warming (AGW) is very tight. However, upon taking the time to get into the details of the science, I was appalled at how flimsy the case really is." Cohen currently serves on the board of directors for CO2 Coalition, a group established in 2015 to counter "the demonizing of CO2 and fossil fuels."