Fatih Birol, chief economist at the 28-nation International Energy Agency, which includes the United States, said that reducing fossil fuel use was crucial to curbing global temperature rise, but added that improving the energy efficiency of homes, vehicles and industry was an easier short-term strategy. He noted that the 19.5 million residents of New York State consume as much energy as the 800 million in sub-Saharan Africa (excluding South Africa) and that, even with President Obama’s automotive fuel standards, European vehicles were on average more than 30 percent more fuel efficient than American ones.

He cautioned that a rapid expansion of renewable power would be complicated and costly. Using large amounts of renewable energy often requires modifying national power grids, and renewable energy is still generally more expensive than using fossil fuels. That is particularly true in the United States, where natural gas is plentiful and, therefore, a cheap way to generate electricity (while producing half the carbon dioxide emissions of other fossil fuels, like coal). Promoting wind and solar would mean higher electricity costs for consumers and industry.

Indeed, many of the European countries that have led the way in adopting renewables had little fossil fuel of their own, so electricity costs were already high. Others had strong environmental movements that made it politically acceptable to endure higher prices in order to reduce emissions.

But Dr. Birol predicted that the price of wind power would continue to drop, while the price of natural gas would rise in coming years, with the two potentially reaching parity by 2020. He noted, too, that countries could often get 25 percent of their electricity from renewable sources like wind and solar without much modification to their grids. A few states, like Iowa and South Dakota, get nearly that much of their electricity from renewable power (in both states, wind), while others use little at all.

So as Europeans have grown accustomed to wind turbines dotting the landscape, much of America continues to regard renewable power as a boutique product, cool but otherworldly. When I tell colleagues that Portugal now gets 40 percent of its electricity from renewable power, the standard response is “Portugal is windy.” But many places in America are, too. When I returned from Kristianstad, Sweden, and marveled at how that city uses waste from farms, forestry and food processing plants to make biogas that supplies 100 percent of its heat, the response is likewise disbelief. But I’d venture that a similar plan could work fine in Milwaukee or Burlington, Vt., cities that also anchor rural areas.

MAPPING studies by Dr. Jacobson and colleagues have concluded that America is rich in renewable resources and (unlike Europe) has the empty space to create wind and solar plants. New York State has plenty of wind and sun to do the job, they found. Their blueprint for powering the state with clean energy calls for 10 percent land-based wind, 40 percent offshore wind, 20 percent solar power plants and 18 percent solar panels on rooftops — as well as a small amount of geothermal and hydroelectric power.