By Madeline Chambers
BERLIN (Reuters) - A former trampolinist and a children's author have led the Greens to a spectacular comeback in Germany, raising the once-unthinkable prospect of a Green chancellor succeeding Angela Merkel.
Tapping mounting concern in Europe about climate change, especially among young people, 'Die Gruenen' won 20.5% of the German vote in May's European Parliament elections, their best-ever result.
Their success has caused convulsions in Merkel's fragile coalition of conservatives and center-left Social Democrats (SPD), who have dominated German politics since World War Two.
"This is in no way just a protest vote or a hoovering-up of Social Democrat (SPD) votes, it's a longer-term trend," said Heinrich Oberreuter, a politics professor at Passau University.
"The advantage for the Greens is they own the issue of climate change which is a long-term problem."
Merkel has lost the status she enjoyed as "Climate Chancellor" for pushing global leaders to address climate change, and the SPD's green credentials have been tarnished by close ties to the coal industry.
Hitting 27%-29% in opinion polls in June, the Greens became Germany's strongest party, spawning headlines about popular co-leader Robert Habeck becoming the chancellor.
That may be a long shot, but they could well join the government and replace the SPD - the junior partner in the coalition - as the main center-left force, say experts.
Inspired by the peace movements of the 1960s and founded in 1980, the party was long dismissed as a fringe group of tree -huggers. Politically, it is closest to the SPD, with which it shared power under Chancellor Gerhard Schroeder in 1998-2005.
A pro-European party that welcomed refugees in the 2015 migrant crisis, it wants a total switch to renewable energy, an end to the combustion engine and higher taxes on SUVs.
The chances of a snap election before 2021 have increased since the European vote when the Greens pushed the SPD into third place. In turmoil, with ratings near all-time lows, the SPD may quit its loveless coalition with Merkel by the end of the year.
Polls suggest the Greens would be big winners in an election.
One option for national government would be a conservative-greens coalition, albeit without Merkel who, after 14 years leading Germany, Europe's biggest economy, says this is her last term.
But radically different positions on energy, tax cuts and migration would pose challenges for such an alliance.
"(It) would need to direct its focus and available financial resources to climate protection and the energy transition," said Deutsche Bank in a research note. "Citizens and corporates cannot hope for major tax relief."
However, the Greens may prefer a left alliance. In a May state election in Bremen, they emerged as kingmaker, but joined hands with the SPD and radical left instead of the conservatives, who had won most votes.
The Greens have won over urban professionals by embracing social issues such as soaring rents in cities, and the leadership duo of scruffy-looking but media-friendly Habeck and less charismatic Annalena Baerbock, is also popular.
"They have a pragmatic, rational political style and so far are acting wisely and keeping internal differences quiet," said Manfred Guellner, head of the Forsa pollster.
Habeck last month overtook Merkel to become Germany's most popular politician. A novelist and children's writer, he is the likelier candidate for the top job, said Guellner.
He and Baerbock, an ex-trampoline competitor who studied international law, brush off questions about their ambitions but acknowledge the pressure is on.
"We have awakened hopes that must be fulfilled. Everyone knows we must deliver," Habeck said after the European election.
On the plus side, they have something of a track record.
In government, the Greens helped usher in a nuclear phase-out and bottle deposits to promote recycling, and they share power in nine of Germany's 16 states.
Yet the road to the chancellery is long. In the 2017 federal election they won just 8.9% of the vote and previous poll highs, especially after the 2011 Fukushima nuclear disaster in Japan, have evaporated fast.
They are weak in the former Communist East, where the far-right Alternative for Germany (AfD) is strong. With some 85,000 members, the party is about a fifth the size of the main parties.
Germans' love affair with the car is also a hurdle.
Keenly aware of the potency of popular movements like the yellow vests in France who opposed fuel tax plans, the Greens will not want to hurt an export-oriented economy that relies on companies like Daimler, BMW, Volkswagen and Porsche.
Plans for a fuel-tax rise cost them votes in 1998.
Winning the chancellery in a spring 2020 election may be a tall order, said Oberreuter, but movements, not traditional parties, have taken hold in France, Austria, Britain and Italy.
"This goes to show that almost anyone can become chancellor - so who knows?" he said.
(Reporting by Madeline Chambers; Editing by John Chalmers)