Welch works as a Partner at the lobbying firm Caliber Strategies. Prior to his time at Caliber Strategies, he worked as a senior legal advisor and counselor to Governors Schwarzenegger, Brown and Newsom at the California Air Resources Board under Chairwoman Mary Nichols. In his role at ARB, he helped lead the creation of multiple industry-friendly climate policies, including the state's cap-and-trade program; the Low Carbon Fuel Standard; and programs to cut methane emissions. Before his time at ARB, Welch helped lead the Environmental Defense Fund’s successful sponsorship of Assembly Bill 32, the California Global Warming Solutions Act of 2006, which provided legal impetus for programs like cap-and-trade and LCFS. He also previously served as a Partner at AJW, Inc. in between stints at the ARB, where he worked to get the cap-and-trade program legislatively extended in 2017 on behalf of clients such as the International Emissions Trading Association.