U.N. Secretary-General Antonio Guterres speaks at the summit to address climate change | Spencer Platt/Getty Images ‘Nature is angry,’ warns UN chief Opening the UN Climate Action Summit, António Guterres says the biggest cost is doing nothing on climate change.

U.N. Secretary-General António Guterres on Monday denounced governments and the fossil fuel industry for fueling climate change, and called for taxing "pollution, not people."

Opening the U.N. Climate Action Summit, meant to spur international climate efforts, Guterres had stark words about the state of the planet. "Nature is angry and we fool ourselves if we think we can fool nature because nature always strikes back and around the world nature is striking back with fury."

The summit comes after millions took to the streets Friday to press for faster action on tackling climate change, and scientists issued yet more dire warnings about the state of the planet.

"There is a cost to everything," Guterres said. "But the biggest cost is doing nothing. The biggest cost is subsidizing a dying fossil fuel industry, building more and more coal power plants, and denying what is plain as day, that we are in a deep climate hole and to get out, we must first stop digging."

He criticized governments for giving "trillions in hard-earned taxpayers’ money to the fossil fuel industry to boost hurricanes, spread tropical diseases, and heighten conflict," as well as plans for building "ever more coal plants that are choking our future."

Governments, instead, must slash carbon emissions to net zero by 2050 to help keep warming to 1.5 degrees.

Guterres spoke ahead of teen climate icon Greta Thunberg, who blasted the assembly for squandering the future.

"People are suffering, people are dying, entire ecosystems are collapsing … and all you can talk about is money and fairytales of eternal economic growth — how dare you," she said.