(George Rose/Getty Images)

In the heart of New York City, among the flash and dazzle of Times Square, there is one sign that is at once a boast and an unintentionally sad reminder of how far the city is from Mayor Michael Bloomberg's ambitious plan for a greener city.

On the billboard, right underneath the bold words "imagination is what drives us to change," is the announcement: "Times Square's only solar powered billboard."

In all honesty, it's a gimmick: America is not driving into a green world - at least not quite yet.

As the sign says, only one of the multitude of screens in Times Square is actually powered by solar energy - pointing out just how far off the dream of having a truly sustainable New York City, or United States for that matter, really is.

PlaNYC

In New York, at least, it's not because the issue hasn't been seriously addressed.

On Earth Day 2007, Bloomberg announced his ambitious PlaNYC for a greener New York, a plan that has since gained international praise as a model for sustainability.

"As a coastal city we're on the leading edge of some of the most dramatic effects of global warming. The science is there - we need to stop debating it and dealing with it," Bloomberg said at the launch event.

Bloomberg's PlaNYC is an effort to make room for a million new people by 2030 while reducing the city's carbon footprint. Since PlaNYC launched, 127 initiatives that creep into nearly every aspect of city life have been started.

New hybrid buses and taxis are making the city a greener place. Hundreds of miles of bike lanes have been added. White roofs that promise to conserve energy are being painted across the city; pedestrian plazas are pushing out cars in Times Square, the Flatiron District and Chelsea. New ferries have been deployed to the East River, connecting outlying boroughs with alternatives to the internal combustion engine. A half a million trees have been planted.

The city has also started an ambitious program of energy retrofits, which includes large skyscrapers like the historic Empire State Building.

"If we don't do anything aggressive, we're going to be dealing with the emissions that we're putting out today for a hundreds of years," Nathanael Greene, director of renewable energy policy at the National Resources Defense Council, told ABC News. "If we dramatically reduce our emissions are we can limit how high the peak emissions are, and what the extreme impacts are from those peak emissions."

One of the biggest successes of the plan has been its ability to combat soot pollution - a problem that kills more people than handguns do.

In order to tackle the problem PLANYC administrators looked at the data and realized that the tens of thousands of buildings in New York City create more soot than all the cars put together.

So administrators developed a project now under way, a collaboration between NGOs, the government, and the real estate industry to figure out how to run buildings on a different type of fuel. So far, 300 buildings have completed upgrades, another 1,000 are on track to complete this year, and 6,000 buildings by 2015.

Bloomberg has said he hopes this will put New York City on track to have the cleanest air of any major city in the world.

However, it's not as green as it could be. Several PlaNYC initiatives - and national initiatives for that matter - are falling far short of their goals. At the cornerstone of the plan is a pledge to cut emissions by 30 percent by 2030. The gorilla in the room remains achieving those emissions reductions.

While U.S. production of renewable energy has increased by more than 300 percent in the past decade, the energy supply for New York and the rest of the country is still dirty. New York is slightly better than the rest of the country, where half of all the power comes from coal, but the city is still highly carbon intensive, relying heavily on natural gas.

According to a new report from the NRDC, "the United States still lags far behind Europe and Indonesia and is only slightly ahead of Mexico in the percentage of electricity it gets from renewable sources."

Losing Ground

In New York City, lack of support for some green initiatives is evident.

A congestion pricing plan to charge $8 tolls for cars entering Manhattan during peak hours is dead. Budgets for improvements for subways, parks and other environmentally friendly infrastructure that could improve the sustainability of the city have been slashed. And many of the candidates expected to run to succeed Bloomberg in the next election seem poised to run against his green agenda.

Still, New York is doing better than most cities.

On a national level, Congress has pulled funds for mass transit and other vital projects, and comprehensive energy legislation is dead in the water. Many U.S. cities are falling short of emissions reduction goals. More than 100 cities across the country have signed up for the Mayors' Climate Initiative - of which PlanNYC is just one example - to reduce greenhouse gas emissions, but few are on track.

"The climate scientists still tell us we need to reduce our emissions by 80 percent from 1990 levels by 2050, which is a complicated way of saying a lot," Greene told ABC News. "By the end of the century we have to be at a carbon-free economy."

Will the US Lag Behind?

America had always been an innovator in the clean-tech arena, dating back to the Carter administration, when the gas crisis gave the United States a wake-up call. The federal government started funding innovation, and as a result much of the clean energy technology used today was invented in the United States.

From large-scale concentrated solar and high efficiency solar cells, to sustainable building practices, for years America was at the forefront of the clean tech race.

However, America remains the only country not to sign onto the Kyoto protocol, refuses to put a price on carbon and has failed to pass long-term legislation to promote renewable energy investments. The country is currently seeing its share of the clean tech market decline.

According to a recent report from the Center for American Progress, titled "America's Future Under 'Drill, Baby, Drill' ," "not only is advanced manufacturing and assembly done in other countries, which control the clean energy supply chains, but these countries are doing the cutting-edge innovation that we once considered one of America's strongest assets."

While at a local level, America "greens its cities," the lack of a clear national energy policy undermines these efforts, and the pace of sustainable development in many cases is not going as far as it should, Greene said.

"This is the typical story for the United States," Greene said. "We lead the world in energy technology innovation, energy business model innovation. Unfortunately, because we don't have a national energy policy, because we don't have a clear commitment to the end deployment of clean energy technologies, a lot of that technology is now being manufactured outside of this country."