Teenage climate activist Greta Thunberg is urging world leaders to acknowledge that global warming “is the biggest crisis humanity has ever faced.”

Thunberg told political and business leaders at a conference in Austria on Tuesday that it’s their job to inform the public about the seriousness of the situation and the need for drastic action.

The 16-year-old Swede said “we must admit that we are losing this battle,” and blasted politicians who talk about climate change before getting onto private jets.

U.N. Secretary-General Antonio Guterres said the world isn’t doing enough to meet the Paris climate agreement’s goal of keeping global warming well below 2 degrees Celsius (3.6 Fahrenheit).

Guterres also called for an end to fossil fuel subsidies, saying taxpayers’ money shouldn’t be used to destroy the planet.