The European Union should spend hundreds of billions of euros combating climate change during the next decade, its chief executive said on Thursday, responding to a Swedish teen who has inspired a global movement of children against global warming.

In a speech alongside 16-year-old Greta Thunberg in Brussels, European Commission President Jean-Claude Juncker also criticised US President Donald Trump for suggesting climate change was "invented" and "ideological".

"In the next financial period from 2021 to 2027, every fourth euro spent within the EU budget will go towards action to mitigate climate change," Juncker said of his proposal for the EU budget, which is typically 1 percent of the bloc's economic output, or 1 trillion euros ($1.13 trillion) over seven years.

"Mr. Trump and his friends believe that climate change is something that has just been invented and its an ideological concept, but ... something dangerous is already underway," Juncker said.

Thunberg was in Brussels to join a seventh week of demonstrations by Belgian children skipping school to protest against global warming.

More than 10,000 students, some holding up banners saying "stop denying the earth is dying", protested across Belgium on Thursday, including in Brussels and the western city of Ghent.

Thunberg said young people around the world wanted politicians to heed scientists' warnings.

"Unite behind the science, that is our demand," Thunberg told a plenary session of the European Economic and Social Committee (EESC). "Talk to the scientists, listen to them."

Trump has cast doubt on the science of climate change. In 2017, he announced his intent to withdraw the United States from the Paris deal to combat climate change, although he cannot quit the deal until after the 2020 presidential election.

The Paris accord aims to limit the global temperature rise to less than 2 degrees Celsius and prevent damaging levels of global warming, which scientists say would limit water availability, alter coastlines and undermine human health.

Trump's new pick to run the US Environmental Protection Agency said last month climate change was not a major crisis.

But Thunberg said she and hundreds of thousands like her were skipping school each week to focus politicians minds on a UN conference in 2020 when countries need to present new plans for more ambitious greenhouse gas emissions cuts.

Students in Germany, Switzerland, France and Australia have followed her lead and also skipped classes to protest, while Thunberg took her protest to last month's World Economic Forum in Davos to galvanize leaders meeting there to action.

Politicians' failure to act "would be the greatest failure of human history and they will be remembered as the greatest villains of all time," she said. ($1 = 0.8813 euros)