Everyone’s favorite McKinsey report states that America can reduce a huge percentage of its carbon emissions through measures that pay for themselves, primarily in the realm of energy efficiency. But it’s never entirely clear how well an analyst’s report is going to translate into reality. For New York City, the answer appears to be: really well.

Mayor Bloomberg’s office recently released a plan to drop the carbon emissions of the municipal government 30% from 2006 levels by 2017. The plan will cost about $2.3 billion, but the city expects to recoup these costs by 2015 — an average payback of less than eight years across a large portfolio of projects.

A full 57% of the savings come from projects related to building retrofits and improved maintenance — utterly boring stuff like boiler replacements, upgraded heating and cooling systems, better steam trap maintenance, etc.

A further 17% comes from wastewater treatment.

Wastewater presently is a huge source of methane. Capturing that methane not only creates a direct reduction in greenhouse gas emissions, but also provides a source of renewable energy.

Another 11% will come from a new rail and barge network to replace long-haul garbage trucking.

The remaining 15% is divided up among a large number of piecemeal initiatives. The sexy, cutting-edge stuff — solar photovoltaic, daylight harvesting, green walls, etc. — make up a tiny sliver of the planned reductions. No breakthroughs required.

The city’s plan calculates the cost per metric ton of carbon dioxide reduced across all the different project types. This metric provides a handy benchmark for any future climate legislation, allowing a direct comparison of financial incentives to costs, as well as a gauge of the economic impact of any carbon reduction effort.