Germany is seen as something of a pioneer in the fight against climate change. Chancellor Angela Merkel has been commended for throwing her weight behind international climate agreements, and the country's push to replace fossil fuels and nuclear power with renewables is famous.

But Germany still has a filthy habit that means its emissions haven't fallen much: coal. And in particular, lignite, or brown coal, which is mined in Germany. It's cheap, and emits more carbon than anything else in the country's energy mix.

Adding its voice to a chorus of environmentalists, an expert advisory council has now urged the German government to start phasing out coal-fired power plants immediately.

"Germany must immediately reduce the coal it burns for power, and stop it completely in the medium term," Claudia Kemfert, a member of the advisory council to the government, said. "The last coal-fired power plant has to be shut down in 20 years at the latest."

Kemfert and her colleagues say the next legislative term could be Germany's last chance to keep global warming below 2 degrees Celsius, in line with the Paris Agreement on climate change.

Even though renewable energy now covers around a third of the country's electricity demand, Germany is set to miss its 2020 target of cutting carbon emissions by 40 percent by 2020 compared to 1990 levels.

Heated debate

For years, environmentalists have protested against Germany's continued dependence on coal. And they are increasingly taking their fight to coal mines in a series of direct actions.

Most recently, activists have occupied a forest to stop it being felled by the RWE power company to make way for coal mining. And in August, thousands of activists from around Europe demonstrated in North Rhine-Westphalia, the heartland of Germany's coal industry.

Environmental advisory council to the German government

But with tens of thousands of people employed in the German coal industry, the threat of job losses and wider economic repercussions have so far prevented politicians from committing to a deadline to ditch coal. And despite growing public pressure, Merkel continues to tacitly support the polluting industry.

Germany's Greens are the only party calling for an immediate start to the coal phase-out. After the September 24 general elections, the environmentalist party is likely be part of the new coalition government - but so is the pro-business Free Democratic Party (FDP), which insists Germany will need to continue burning fossil fuels for the foreseeable future.

Merkel's conservatives are currently in coalition talks with the Greens and the FDP and it remains to be seen if the coalition agreement will broach the coal issue. But the advisory council says the new government must take action.

International responsibility

The council has calculated that to keep within the 2-degree target, German coal power stations must not emit more than 2,000 megatons of CO2. That's around 10 times their combined annual emissions - giving them 10 years running time before they push Germany over the limit.

If coal emissions could be limited to 2,000 megatons of CO2, "Germany would just about fulfil its part of the minimal goal [of 2 degrees]," Wolfgang Lucht, researcher at the Potsdam Institute for Climate Impact Research and member of the advisory council, told DW.

"Ideally, we would manage to achieve the goal of 1.5 degrees Celsius by emitting less," he added. To reach the more ambitious 1.5-degree goal, Germany would have to shut down all its coal-fired powered plants within the next two and a half years.

However, these calculations ignore Germany's historic emissions. Taking into account the CO2 the country has already emitted, the study calculated that "Germany has already used up or significantly exceeded its total emissions budget."

Coal exit in three phases

Accepting that the immediate shut-down of Germany's coal operations is politically impossible, the experts proposed a gradual strategy to wean the country off coal.

First, the oldest, most inefficient - and therefore climate-damaging - plants should be closed by 2020. The study says this would give Germany a chance of meeting its 2020 climate targets.

Remaining coal power stations would be kept online with decreased production, as a back-up to guarantee a stable electricity supply, and shut down one by one until the last closed in 2030.

The plan echoes Germany's gradual phase-out of nuclear, which will see the last nuclear power plant shut down in 2022. As with the nuclear phase-out, the study recommends the government work towards a consensus between affected regions, companies, labor unions and environmental organizations.

Next year a "coal commission" is to start looking at possible strategies to give up coal and how the phase-out would impact those dependent on the industry. But environmentalists fear this may be a lengthy process.