Mayor Michael Bloomberg just announced a radical plan: make the city's entire fleet of yellow cabs green by the year 2012. He also announced plans to require that all black limousines (about 10,000 city-wide) meet fuel-efficiency standards, which means that all those shiny black chariots parked outside of Goldman Sachs, Lehman Brothers, and a host of other Fortune 500 corporations in New York will be joining the fray in helping greenify the planet.

It's hard to believe this is the same mayor who just six years ago tried to end recycling to save money.

The cars currently travel just 12-15 miles per gallon; Bloomberg is requiring that they get 25 miles by next year and 30 by 2010. This will only be feasible if they become hybrids, according to news reports. Of the 13,000 yellow cabs currently licensed in New York, under 1,000 are hybrids. That may not be a lot, but remeber: it wasn't long ago that none were hybrids, and not long before that when cabs looked more like small tanks. Remember Travis Bickle's checkered cab in Taxi Driver?

There is one paradoxical piece of the puzzle that worries me, however. In order to ensure that all the cars licensed by the New York City Taxi and Limousine Commission leave as small a thumb print as possible on the environment, they'll need to be retired after just six years.

Do the math: 13,000 yellow cabs + 10,000 limousines + 40,000 livery cabs = 63,000 cars. If each car weighs in at around 2,000 pounds, that's 126,000 pounds of metal, plastic, and electronic waste we'll be producing in New York City alone every six years.

This might not hurt the ozone, but it can't be good for our land. Bloomberg has made a lot of great decisions for the city since his 2001 election, and this can be counted among them. But we'd all be wise to keep an eye on the underbelly of environmentally motivated initiatives. If our green-colored glasses are too deeply tinted, we might as well be blind.