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:

Trump touts $5,000 payout if Republicans win as Vance waits in wings
Search expands after Philippine ferry fire kills five and leaves dozens missing
Trump says Iran war to end after US midterm elections
At least 20 killed in cargo vessel fire at China shipyard, state media reports
US military says it struck vessel in Caribbean, killing 3
At least 14 killed in explosion at weapons depot in Syria
US hits five Iranian oil tankers after attack on Navy ships
UK gives air traffic provider a week to probe outage that halted flights
