Instead of cutting greenhouse gas emissions 20 percent by 2010 — the goal of a Climate Protection Plan adopted three years ago — the city believes it has increased its emissions by at least 17 percent.

Next month, the city is trying again, convening a Cambridge Climate Congress of citizens to pin down what can be done to reverse the trend locally. Organizer John Pitkin, a Harvard Square demographer who ran for City Council in 2003, said while there have been major commitments to going green since the 2002 plan was announced, “there was not nearly enough buy-in, not only from businesses, but from residents.”

Harvard University has vowed a 30 percent reduction in its emissions by 2016, for instance, and Pitkin believed the city itself has made good progress, but the 2002 plan failed in that there “never was a way of drawing all the important emitters and getting them to actually do stuff.”

This time, there will be no such mistake.

A Dec. 12 meeting will focus on education and goal setting, Mayor Denise Simmons said in a press release today, and an entire follow-up session Jan. 23 will — according to Pitkin — “be more about implementation and to try to get large organizations and businesses to make specific commitments.” Findings from the meetings will also be presented to the City Council, state and federal governments and to next year’s International Climate Change Adaptation Conference in Copenhagen.

Those who want to take part can click here or call Muna Kangsen in the mayor’s office at (617) 349-4321 to submit a paper application before Dec. 2. Organizers hope for between 75 and 100 delegates.

Uniquely, Simmons is organizing events that will culminate when she is no longer mayor. But she has support for this from seven of the most recent Cambridge mayors before she took office: Barbara Ackermann, Francis Duehay, Anthony Galluccio, Kenneth Reeves, Sheila Russell, Michael Sullivan and Alice Wolf.

“I asked my predecessors to help me guide this extraordinary effort, in part because their combined endorsement adds the proper sense of gravity to the situation, and partially to ensure continuity by serving on an advisory committee,” Simmons said. “Their participation will help us attract participants from across the Cambridge community, and it is important that we get people who truly represent all the different faces of our city.”