Hershkowitz started working at the Natural Resources Defense Council around 1988. In 2007, the Academy of Motion Picture Arts and Sciences approached the NRDC for advice about how to reduce the carbon footprint of the Oscar Awards show, after the academy was asked to do so by one of the producers of An Inconvenient Truth. Hershkowitz, in his role as a senior scientist at the NRDC, helped them from 2007 to 2011. Similarly, The Recording Academy asked the NRDC for help greening the Grammy Awards starting in 2008, and Hershkowitz led that effort as well. At an NRDC staff retreat in 2004, board member Robert Redford suggested that the NRDC establish more of a presence at professional sporting events; Hershkowitz told a reporter from Mother Jones: "We were trying to figure out how to reach out to untraditional allies, and Redford says to us, 'You know, if you want to meet Americans, you’ve got to go to a baseball game or a football game. You’ve got to go to one of these stadiums. That’s where America is.'" Hershkowitz met with Bud Selig of the Major League Baseball shortly after that, and soon the NRDC was creating white papers and teams to advise all the major sports leagues about environmental sustainability initiatives that addressed each sport's needs and could help them save money. Hershkowitz eventually ran the Sports Greening Initiative at the NRDC. The Green Sports Alliance got started in the late 2000s as informal discussions among management of sports teams in the Pacific Northwest, about how to improve their operations' sustainability. The idea of formalizing an alliance was generated in a meeting between Hershkowitz and representatives of sports teams owned by Paul Allen via Vulcan Inc., and GSA formally launched in the spring of 2011, with NDRC as one of the founding organizations. In 2014 Hershkowitz left the NRDC and became president of the GSA. In December 2015, Hershkowitz was listed as the 50th most influential person in the field of sports business by the Sports Business Daily, which was the first time he had been on the list. By the time of the listing, he had provided environmental sustainability advice to the NBA, the NHL, MLB, Major League Soccer, and the U.S. Tennis Association that, according to the listing, had saved the leagues millions of dollars. In December 2015, the GSA under Hershkowitz's leadership helped organize two summits on sports sustainability at the 2015 United Nations Climate Change Conference The participation of representatives from major American professional sports associations marked the first time the sports industry were directly involved with climate change initiatives by the United Nations. In June 2016 Hershkowitz left the GSA to focus on more global issues. In December 2016 Sports and Sustainability International was formally launched; Hershkowitz was a member of its organizing committee, along with four other founding directors.
