Still, the most recent projections show Germany will need to cut an additional 22 million metric tons of carbon emissions within the next five years if it is to meet its targets. Germany’s energy ministry in December proposed closing the gap by imposing penalties on the oldest lignite coal-fired power plants that are the prime emitters.

In response, 15,000 miners traveled in buses to the German capital in late April, blowing whistles and waving banners to denounce the proposal, which union leaders said would mean a loss of thousands of jobs.

Officials in Berlin recently adopted an alternative, drawn up in consensus with unions and industry leaders. Instead of being required to cover the full gap of 22 metric tons, the industry will be expected to reduce carbon emissions by about half that.

The difference is to be made up largely through subsidies to improve efficiency in heating generation and consumption, which could prove more costly to consumers.

The alternative plan comes as Germany looks to the next chapter of its emissions reduction program: cutting greenhouse gas emissions to 55 percent of 1990 levels by 2030, while at the same time increasing renewable sources to about 50 percent of energy production.

“We are now headed into a more challenging phase of the energy transition,” said Patrick Graichen, who heads Agora Energiewende, a research center in Berlin devoted to explaining the energy transition program. “Reaching the first 25 percent went swiftly, as they were largely absorbed by the existing system. But now reaching the 50 percent mark will mean transforming the system.”

Shutting the nuclear plants, which do not emit carbon but have other risks, would seem to be contradictory at such a time. Ms. Merkel surprised many in 2012 when she reversed an earlier policy, announcing the immediate closing of eight nuclear power plants and plans to shutter the remaining nine by 2022.