Mayor Bill de Blasio unveiled a plan yesterday to make the Big Apple the world's greenest metropolis.

About 3,000 schools, government offices and other city buildings will be retrofitted over the next 10 years to reduce greenhouse gas emissions.

The mayor estimated that 3.4 million metric tons of gas a year will be eliminated and it will save the city $8.5 billion by 2025. "Only by ratcheting up our standards and demanding more of ourselves and making more radical changes are we going to save the day. It is possible," he told reporters before he participated in the People's Climate March through the city yesterday.

As part of the proposal, de Blasio said that his administration will work with the private sector to help them adapt their properties as well.

The mayor set forth a long-term goal to reduce greenhouses gas emissions in the city by 80% by 2050, and said he was confident future policies will help meet this deadline.

City Councilman Donovan Richards, who chairs the environmental committee, said the building retrofit plan was a great step in the right direction.

"It's a win for New York City, it's a win for the communities who have been looking for this," said the councilman, who represents the Rockaways.