BRUSSELS (Reuters) - Thousands of Belgian students skipped classes for the fourth week in a row on Thursday to protest against global warming, part of a growing youth protest around the world.

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Beating drums, chanting and carrying signs, some 30,000 teenagers braved the cold in Brussels and other cities to call on local politicians for stronger action to prevent climate change.

“It’s our planet and the generation before us hasn’t done anything,” said Julian Rume, 17. “In 20, 30 years, we will all be migrants, we’ll all be moved out of our planet.”

The demonstrations are part of a broader grassroots movement started by Swedish student Greta Thunberg, 16, last year.

Students in Germany, Switzerland, France and Australia have followed her lead and also skipped classes to protest.

Thunberg took her protest to this month’s World Economic Forum in Davos to galvanize leaders meeting there to action.

While Thursday’s march in Brussels drew fewer people than last week, demonstrations spread to other cities, with some 15,000 students in the streets of Liege, according to police.

“The climate is a disaster,” said demonstrator Allison Debonte, 15, adding that she fears her children will not be able to live in Brussels due to climate change.

One student held a sign saying: “It’s you who decided... it’s us who will suffer.”

The student demonstrations have been supported by many political figures and personalities including Belgium’s King Phillipe. They are part of rolling protests urging greater action in recent weeks, as extreme temperatures fuel concerns that climate change is gathering pace.

On Sunday, two months since the first demonstration, some 70,000 people rallied in Brussels. Organizers are urging European leaders to adopt ambitious climate policies in line with goals set by the Paris agreement in 2015.

The Paris climate agreement, adopted by almost 200 nations, set a goal of limiting warming to “well below” a rise of 2 degrees C above pre-industrial times while “pursuing efforts” for a tougher goal of 1.5 degrees C.

Brussels has been regularly ranked as one of the most congested cities in western Europe due to its high population density and large number of commuters.

That is a mark of shame for a capital where the EU sets European climate policies.