Last night the protesters camped out on the Wetstraat, Belgium's political nerve centre. But the police cordoned off the encampment. The protesters say they are eager to camp out at a location that is more accessible.
Greenpeace's Joeri Thijs: "Last night was a tremendous success. Some 100 people spent the night here. In consultation with the police we've decided to switch to the Troonplein. There we're organising a breakfast and we're asking the people of Brussels to join us."
The situation in the Wetstraat was described as "difficult".
"We weren't allowed to bring in any more tents or sleeping bags. Ordinary citizens couldn't reach us. But that's exactly what we do want."
Anuna De Wever, the girl behind Youth For Climate and the Belgian teen protests also joined in. She didn't get too much sleep and has now gone to school.
"This climate law must be introduced. If it isn't it's an insult to all the people who take to the streets every week. It was so cold. I hardly slept. We're not doing this for fun! We'll make our point until they listen."
The protesters want a change in the constitution after Belgium's council of state ruled that a federal climate law setting out binding targets would be unconstitutional as environment is a regional power. Francophone parties favour the change but most centre right Flemish parties are against. They argue that a law with binding goals isn't the way to sort the matter, but that legislation on individual measures is needed.
A two thirds majority is required to change the constitution in Tuesday's vote, but this will not be reached.