The German government's flagship climate protection plan is "insufficient" and has to set clear goals for reducing greenhouse gas emissions after 2030, Germany's highest court ruled Thursday, marking a major setback for Angela Merkel's right-left coalition in an election year when environmental issues are expected to take center stage.

In a decision hailed by activists as "historic" and "sensational," Germany's Constitutional Court ruled that Berlin's current goal of reducing CO2 emissions to 55% of 1990 levels by 2030 was "incompatible with fundamental rights" because it failed to cover the years beyond this decade.

The current measures "violate the freedoms of the complainants, some of whom are still very young" because they "irreversibly offload major emission reduction burdens onto periods after 2030," the court ruled, partially upholding a series of claims by environmentalists and young people.

It argued that while the state had not violated its duty to protect citizens against climate change, the government had nonetheless not set out the timeline for further emissions reductions in enough detail.

The risk of "serious burdens" being put on generations beyond 2030 was therefore significant, the court said.

Berlin must "at the very least determine the size of the annual emission amounts to be set for periods after 2030," the court ruled, saying an improved plan must be put forward by Dec. 31, 2022.

The stunning ruling came at a time when a debate over environmental policies was already heating up with the Greens party enjoying a surge in popularity and overtaking Merkel's conservatives in several opinion polls over the last week.

Annalena Baerbock, the leader of the Greens gunning for Merkel's job, hailed the court's decision as "historic."

"The coming years will be decisive for meaningful action," tweeted the 40-year-old, who could become Germany's first Green chancellor if her party maintains its upward momentum.

Nine young claimants

Besides an emissions target for 2030, Germany's new climate change law introduced by Merkel's government in 2019 includes a range of policies, including incentivizing renewable energies, expanding electric car infrastructure and carbon trading.

The law was passed in order to comply with the 2016 Paris Agreement, under which countries aim to keep the global temperature increase to under 2 degrees Celsius (36 degrees Fahrenheit), and ideally closer to 1.5 degrees, by 2050.

Germany said last month it had met its annual climate goals set out by the law in 2020, in part due to a reduction of activity during the coronavirus pandemic.

Yet activists have long argued that the law does not go far enough, prompting a series of legal claims against the government to toughen the measures.

Supported by Greenpeace and leading German Fridays for Future activist Luisa Neubauer, the claimants included a group of nine young Germans whose families' agricultural or sustainable tourism businesses have been threatened by heatwaves and floods.

"We have won! Climate protection is not a nice-to-have, it's a fundamental right," tweeted Neubauer, 25, in reaction to the ruling.

The claimants' lawyer Roda Verheyen said that the court had "set a new global benchmark for climate protection as a human right."

Green surge

The government also appeared to welcome the ruling, with conservative Economy and Energy Minister Peter Altmaier calling it an "epochal" decision for "climate protection and young peoples' rights," which would also give "planning security to business."

Environment Minister Svenja Schulze of junior coalition partner Social Democrats said the decision was an "exclamation mark for climate protection."

Yet the decision in fact heaps further pressure on the government at a time when the environmentalist Green Party has taken a surprise lead ahead of September's general elections.

On a regional level, the Greens are already part of government coalitions in more than half of Germany's 16 states, including in prosperous Baden-Wuerttemberg, home of auto giant Daimler.

Backed by young activists, including students who had rattled the political establishment with school strikes for climate protection, the ecologist party's meteoric rise appears unstoppable.

Baerbock has pledged to make climate protection the benchmark for policies across all sectors.

In contrast, Armin Laschet, the leading candidate for Merkel's CDU party, has been accused of neglecting environmental policies.

"It's not enough to see the environment as mere decoration, it is a central issue," said his rival Markus Soeder amid a bitter battle for the conservative nomination earlier this month.