Thousands of schoolchildren are marching through Berlin to urge tougher measures against global warming.
Smaller protests have been organised in Switzerland, inspired by 16-year-old Swedish activist Greta Thunberg. She is in Davos, urging the World Economic Forum (WEF) to ensure a greener future.
On Thursday, 35,000 teenagers marched in Brussels against global warming.
Thousands of school pupils went on strike in Switzerland a week ago to demand climate action.
In Brussels, home to the main EU institutions, students carried banners with slogans such as "Dinosaurs thought they had time too" and "Be part of the solution, not the pollution".
German students are mobilising with the Twitter hashtag #FridaysForFuture. A popular slogan was "There's no planet B".
Their protest coincides with government talks on how best to reduce Germany's reliance on coal and boost renewable energy sources.
The young activists are urging world leaders and corporate bosses to stick to the ambitious goals agreed in Paris in 2015 to combat climate change.
What is Greta's message?
Since August, Greta Thunberg has been sitting outside the Swedish parliament every Friday to get her climate message across.
She took a train all the way from Sweden to Davos, which took 32 hours, underlining the need to use cleaner forms of transport. Jets emit especially high quantities of CO2.
She has drawn some criticism on social media: some accuse her of encouraging truancy, publicity-seeking and doing the work of environmental lobbyists.
But one of her young German supporters, Jakob Blasel, said combating climate change was "for us more important than education".
"After all, why should we study if we have no future?" he asked.
In the Swiss ski resort Ms Thunberg told business leaders: "Some people, some companies, some decision-makers in particular have known exactly what priceless values they've been sacrificing to continue making unimaginable amounts of money… and I think many of you today belong to that group of people."
Speaking later to the BBC she said: "My message was that most emissions are caused by a few people, the very rich people, who are here in Davos."
She said her criticism prompted nervous laughter and applause among the rich and powerful gathered there. Many of them flew in to Davos on private jets.
"These people have very much power, they could really change something, so I think they have a huge responsibility. They need to put their economic goals aside to safeguard the living conditions of humankind in the future," she told the BBC.
She also said Sweden "is not a role model - it's one of the top ten countries in the world with the highest ecological footprints per capita".