A petition calling on the Belgian government to strengthen its climate policy has already been signed by 100,000 people.
Meanwhile, thousands of Belgian students will again be skipping class for the sixth week in a row.
They're also demanding a better climate policy.
Kevin Ozebek has more from Brussels:

Ukraine seeks exchange of 1,200 prisoners with Russia
Blast at police station in Indian Kashmir kills nine, injures 27
Indonesia landslide kills 11 in Central Java, official says 12 missing
Trump says he will likely sue the BBC for up to $5 billion over edited speech
Several people killed as bus crashes into stop in Stockholm
