The city did just announce a major cycling initiative - 200 more miles of bike lanes in 3 years. The next best step is to adopt the legislation allow bikes into all buildings and set up better parking facilities around the city for cyclists.

And yes, reducing reliance on the automobile for everyday transportation needs is really the key to reducing the cabon output of the city. Improving energy efficiency around the city is also very important, especially heating and electrical  systems.

But let me flip your observation about the power and influence that New York has as a consumer of resources from elsewhere. We can make decisions on what we choose to buy from the surrounding areas and the rest of the world to influence decisions made at the site of production. NYC's power as an large market can project a huge influence on our suppliers and create whole new industries and patterns of economics that favor more sustainable agriculture, less packaging, better recycling, more efficient transportation of goods, etc.

For instance, NYC spends something like $25 Billion on food every year in grocery stores, restaurants and other places. Changing just a fraction of where that $25 Billion gets spent can influnce what farmers grow and how they grow it to be much more sustainable than it currently is.

New York is quickly becoming the new center of the urban environmental movement. It's massive size in population & economics as well as it's influence in the media have the  potential to be a major force in influencing sustainable development across the rest of the US.