Rohit Aggarwala has done everything from taxing plastic bags and promoting CFLs to overseeing congestion pricing and green building guidelines. While Aggarwala’s projects have met with varying degrees of success during his four-year tenure as the Bloomberg administration’s chief futurist, few people have done more to alter the conversation about environmentalism and urbanism in the city during that span. But now someone will have to try and fill Aggarwala’s estimable green shoes, as the Bloomberg administration announced yesterday that he would be leaving for the West Coast.

“He transformed the city from a place that talked about the environment to a place that did something about it,” Rick Bell, executive director of the AIA New York chapter, said in an email. When asked for his thoughts by phone, Russell Unger, head of the Urban Green Council, replied, “Am I allowed to cry?”

Aggarwala joined the administration in 2006 from monolithic consultancy McKinsey with the responsibility of launching the Office of Long-term Planning and Sustainability and with it PlaNYC, the wide-ranging blueprint released on Earth Day the following year that strives to reduce the city’s emissions by 30 percent by 2030. Since then, he has spearheaded individual initiatives helping realize the 127 points in the plan, coordinating efforts across agencies and at the City Council, coming up with new ways of reaching the goals both big and small, and just generally changing the city’s thinking about its future, both environmental and in general.

“I’ve often said that Rohit was the brains behind PlaNYC,” Mayor Michael R. Bloomberg said in a statement. “He is a farsighted and creative thinker whose inspiration and work ethic allowed us to develop and then put in place a 20-year vision for improving the City that our children and grandchildren will inherit.”

While Aggarwala has been applauded for his data-driven approach, it also has its detractors, like other Bloomberg directives at the Department of Education and City Planning. Some say he prefers quick fixes—say white roofs over green ones—and that the big initiatives remain frameworks or recommendations as opposed to actual, implemented legislation. Still, Aggarwala’s star power will likely help him find a job not far from his wife-to-be (the wedding is in a week), who is becoming a fellow at Stanford, which necessitated the move.

As for his replacement, Unger believes Aggarwala has set a daunting precedent. “To do this job takes a mix of skills you often don’t find together,” he said. “You need great vision and management skills and the ability to negotiate, and those don’t often go together. They could get a big thinker or a technician to do this job, but finding a big thinker who’s also a technician is a big challenge.”

That said, Aggarwala has done so much to promote sustainability, it could be hard for the city to move away from it. “Everyone looks to New York now as a leader in sustainability,” Unger said. “Thanks to Rohit, this has gone from a B or C issue at City Hall to A level, a top priority. That should make it easier to find the top talent we need to keep this up.”