A couple of years ago, the smart money was on wind. In 2012, 13 gigawatts worth of wind-powered electricity generation capacity was installed in the United States, enough to meet the needs of roughly three million homes. That was some 40 percent of all the capacity added to the nation’s power grid that year, up from seven gigawatts added in 2011 and just over five in 2010.

But then a federal subsidy ended. Only one gigawatt worth of wind power capacity was installed in 2013. In the first half of 2014, additions totaled 0.835 gigawatts. Facing a Congress controlled by Republicans with little interest in renewable energy, wind power’s future suddenly appears much more uncertain.

“Wind is competitive in more and more markets,” said Letha Tawney at the World Resources Institute. “But any time there is uncertainty about the production tax credit, it all stops.”

Wobbles on the road to a low-carbon future are hardly unique to the United States. In its latest Energy Technology Perspectives report, the International Energy Agency noted that the deployment of photovoltaic solar- and wind-powered electricity was meeting goals established to help prevent temperatures from rising more than 2 degrees Celsius (3.6 degrees Fahrenheit) above the average in the preindustrial era, the limit agreed to by the world’s leaders to avoid truly disruptive climatic upheaval.