BERLIN — When protesters in reflective yellow vests took to the barricades in France, rebelling against a gas tax that would hit hardest those who could least afford it, Annalena Baerbock was watching closely from across the border.

A co-leader of Germany’s Greens, Ms. Baerbock has seen her party steadily strengthen over the last year. But she knows if the Greens are to become a bigger force, they will have to convince voters that climate policy is not an elitist but a common cause, while also addressing their economic concerns.

“The lesson from France is that we cannot save the climate at the expense of social justice,” said Ms. Baerbock, who at 38 is roughly the same age as her party. “The two things need to go hand in hand.”

This is the Greens’ moment in Europe, or at least it could be.

The Greens now routinely beat Chancellor Angela Merkel’s conservatives in the polls and are widely expected to be part of the next German government. In recent European elections, Green parties gained significantly in other corners of the Continent, too, winning 63 out of 751 seats in the European Parliament, an increase of about 47 percent.