Setting global emissions targets, however, has proved elusive for years, and the latest assessment of Europe’s progress illustrates that once targets are reached, significant difficulties remain in holding countries to their agreed-to goals.

Even a country like Germany, where support for the environment borders on a religion, has faced unforeseen challenges as it aims to revamp its energy sector from reliance on traditional sources of energy, such as nuclear and fossil fuels, to renewable sources, including wind, solar and biofuels.

The race to shutter the country’s nuclear reactors by 2022, for example, has resulted in many power providers using brown coal, or lignite, the cheapest and dirtiest of all fossil fuels to keep the power flowing to customers. This, in turn, has led to an increase in carbon emissions.

According to the report, Germany, whose economy is the best in Europe, was the only country with a significant rise in both its emissions reductions and energy consumption last year. Along with Belgium, it is one of only two countries not on track to meet its 2020 targets in either category. According to the German Association of Energy and Water Industries, the country increased its carbon omissions by 20 million tons from 2012 to 2013, instead of reducing them.

In order to meet its goals, Germany must reduce emissions annually by 3.5 percent over the next six years, a feat that will result in substantial increases in energy costs, and generate political pressure to block measures that could hurt the economy.

Harro van Asselt, a researcher at the Stockholm Environment Institute’s Oxford Centre, said Germany saw a drop in emissions after many polluting industrial sites in the former East Germany were shuttered between the late 1990s and early 2000s. The closings occurred just as Europe began tackling climate change, which assisted the European Union in meeting its 2020 targets, he said.

“The question is not why they might stumble now; the main question is why did they reach their targets before,” Mr. van Asselt said.