DAVOS • Greta Thunberg brought a stark message to the business elite gathering in Davos yesterday: Everybody is talking about climate change, but nobody is doing anything.

Her appearance at the opening of the World Economic Forum was a striking sign that the debate about how to stop the earth warming has become mainstream in business circles.

Yet only a handful of executives from the oil, gas and coal industries that are chiefly responsible for warming the planet were seen attending the panel at which Greta spoke yesterday.

"The climate and environment is a hot topic right now, thanks to young people pushing," 17-year-old Greta said at the Swiss ski resort, where about 3,000 business and political leaders gather each year.

"Pretty much nothing has been done, since the global emissions of CO2 have not reduced."

Hours after she spoke, United States President Donald Trump took aim at the "perennial prophets of doom" on the environment, telling the forum that warnings of the climate crisis were "foolish".

"We must reject the perennial prophets of doom and their predictions of the apocalypse," Mr Trump said, with Greta in the audience.

The Swedish activist's words came as the World Economic Forum sounds alarm bells on climate change.

This year and for the first time on record, environmental risks occupy the group's top five long-term concerns, while corporate executives say they are increasingly concerned about environmental issues.

But young activists at Davos said none of this is enough. Greta is giving relevance to the Davos gathering, which for years has suffered from criticism that it was largely a billionaires' playground where the rich debated among themselves without hearing outside voices.

Hundreds of climate activists were due to arrive at Davos on foot yesterday following a three-day march across the Swiss Alps.

Protesters will gather at the ski resort and stage a demonstration calling for the end of the World Economic Forum.

BLOOMBERG, AGENCE FRANCE-PRESSE