SAN JOSE, Costa Rica — Long heralded as a tiny country with a tenacious commitment to bettering the environment, Costa Rica now intends to win the greenest of honors: to become the first country to go entirely carbon neutral by 2021.

From the northern Caribbean canals of Tortuguero to the lush southwest Osa Peninsula, going green has long been the mantra. The country's national tourism campaign slogan is "Costa Rica, no artificial ingredients." Nearly all the electricity consumed by Ticos is renewable, with as much as 80 percent generated by hydroelectric power

Lifting the country's entire CO2 footprint is widely seen as the next frontier — and Costa Rica isn't alone in this race. Other green Samaritans include Iceland, New Zealand and Norway.

However, a chorus of skeptics — including scientists, environmentalists and even some of the c-neutrality plan’s supporters — is chiming in about Costa Rica's chances. Though households are fueled by cleaner energy, Costa Rica's vehicles continue to guzzle gasoline. As automobile ownership booms, emissions are rising faster than they can be offset.

Costa Rica has focused much of its effort to remove its carbon footprint on growing forests, which capture CO2 naturally. Worldwide deforestation accounts for as much as 20 percent of global carbon emissions, according to Rainforest Alliance, an international conservation organization.

But Orlando Chinchilla, director of the National University’s Institute for Forestry Research and Services, thinks there simply is not going to be enough space remaining to grow vegetation needed to offset Costa Rica’s emissions.

"The whole country isn't going to be reforested. We need to leave room for houses and infrastructure, to plant crops like rice and beans, not to mention the African palm or pineapples,” Chinchilla said.

In the mid-1980s, forests covered about 20 percent of Costa Rica. Through robust reforestation and conservation projects, woods have sprawled to about 50 percent. In one of the programs, the government uses money collected from a gasoline tax to pay landowners to preserve trees on their property or plant new ones.

In the city, however, it's a different story. In the greater metropolitan area around San Jose, exhaust-spewing buses, cars and motorcycles battle for space along the potholed streets. These are the country's big polluters, accounting for as much as 70 percent of CO2 emissions, according to a recent study by CO2neutral2021.org, an NGO consisting of young Costa Rican professionals who seek to help steer the country toward its no-footprint goal.

Riding the boom of Costa Rica's middle class, automobile ownership in the past decade has gone from one car for every 10 Ticos to one in four, the study found.

A tough new traffic law, introduced at the end of 2008, could help cut auto pollution by restricting driving at key points of congestion in the San Jose area, but a series of legislative hurdles have slowed its implementation.

CO2neutral2021 proposes a host of alternatives, including an improved bus system, biofuels, electric cars and better urban planning to avoid car dependency. It also calls for the construction of an efficient electric railway, plans for which are already underway for the greater San Jose area, with almost a dozen international rail developers knocking on Costa Rica's door to carry it out.

“If Costa Rica is able to become a low-carbon economy ... it will bring significant economic benefits to the country,” said Roberto Jimenez, a recent Yale M.B.A. graduate who is the strategy manager of CO2neutral2021.

He said that reducing the number of gas-guzzling automobiles will cut down Costa Rica's need for foreign oil, which he stressed is fueling the country's inflation, which is among the highest in Latin America. He said it would also create jobs related to creating a greener economy.

President Oscar Arias appears to be aware of the rewards. In a September speech before the United Nations titled "It's cheaper to save the planet than to destroy it," he pressed countries to act now to slash carbon emissions and promote renewable energies.

“We don’t have 20, 40 or 60 years to radically change things. We have, at most, eight years,” Arias said at the summit, which was a warm-up for the Copenhagen Climate Conference in December.

By the 2020s, Central America's treasured biological corridor could see pronounced effects by global warming, according to a recent study by the Water Center for the Humid Tropics of Latin America and the Caribbean. The study, funded partly by United States Agency for International Development, suggested that forests will decline, wiping out thousands of plant and animal species.

Though skeptics and proponents alike doubt that the bold c-neutrality benchmark will be reached, most agree it is nonetheless important to lower emissions to try to make a difference. All eyes will be on Copenhagen to see if other nations choose to join the race.