Demonstrators take part in a protest against climate change, organised by the YouthStrike4Climate movement, in London, Britain March 15, 2019. REUTERS/Henry Nicholls

Students take part in a protest against climate change in Athens, Greece March 15, 2019. REUTERS/Costas Baltas

A demonstrator, wearing a mask depicting U.S. President Donald Trump, takes part in a protest against climate change, organised by the YouthStrike4Climate movement, in London, Britain March 15, 2019. REUTERS/Henry Nicholls

Students take part in a "youth strike to act on climate change" demonstration in Paris, France, March 15, 2019. REUTERS/Gonzalo Fuentes

Students take part in a "youth strike to act on climate change" demonstration in Paris, France, March 15, 2019. REUTERS/Gonzalo Fuentes

A student demonstrates to demand global action on climate change as part of the "Fridays for Future" movement in Rio de Janeiro, Brazil March 15, 2019. The sign reads:"Renewable." REUTERS/Sergio Moraes

Demonstrators take part in a protest against climate change, organised by the YouthStrike4Climate movement, in London, Britain March 15, 2019. REUTERS/Henry Nicholls

Demonstrators take part in a protest against climate change, organised by the YouthStrike4Climate movement, in Brighton, Britain March 15, 2019. REUTERS/Peter Nicholls

Students take part in a "youth strike to act on climate change" demonstration in Paris, France, March 15, 2019. REUTERS/Gonzalo Fuentes

Students demonstrate to demand global action on climate change as part of the "Fridays for Future" movement in Madrid, Spain, March 15, 2019.REUTERS/Susana Vera

Students take part in a "youth strike to act on climate change" demonstration in Paris, France, March 15, 2019. REUTERS/Gonzalo Fuentes

A participant holds up a sign during a demonstration against climate change in Zurich, Switzerland March 15, 2019. REUTERS/Arnd Wiegmann

Student holds a placard as she demonstrates to demand global action on climate change as part of the "Fridays for Future" movement in Riga, Latvia March 15, 2019. REUTERS/Ints Kalnins

A demonstrator takes part in a protest against climate change, organised by the YouthStrike4Climate movement, in London, Britain March 15, 2019. REUTERS/Henry Nicholls

Students take part in a "youth strike to act on climate change" demonstration in Nice, France, March 15, 2019. REUTERS/Eric Gaillard

Demonstrators take part in a protest against climate change, organised by the YouthStrike4Climate movement, in London, Britain March 15, 2019. REUTERS/Henry Nicholls

Demonstrators take part in a protest against climate change, organised by the YouthStrike4Climate movement, in Brighton, Britain March 15, 2019. REUTERS/Peter Nicholls

Demonstrators take part in a protest against climate change in central Brussels, Belgium March 15, 2019. REUTERS/Yves Herman

Students take part in a "youth strike to act on climate change" demonstration in Paris, France, March 15, 2019. REUTERS/Gonzalo Fuentes

Demonstrators take part in a protest against climate change in central Brussels, Belgium March 15, 2019. REUTERS/Yves Herman

Students take part in a "youth strike to act on climate change" demonstration in Paris, France, March 15, 2019. REUTERS/Gonzalo Fuentes

Students demonstrate to demand global action on climate change as part of the "Fridays for Future" movement in Madrid, Spain, March 15, 2019.REUTERS/Susana Vera

Students take part in a "youth strike to act on climate change" demonstration in Paris, France, March 15, 2019. REUTERS/Gonzalo Fuentes

Demonstrators take part in a protest against climate change organised by the YouthStrike4Climate movement in Durban, South Africa March 15, 2019. REUTERS/Rogan Ward

Participants gather for a demonstration against climate change in Zurich, Switzerland March 15, 2019. REUTERS/Arnd Wiegmann

Activist Greta Thunberg speaks during the global demonstration "Global strike for future" in central Stockholm, Sweden, March 15, 2019. TT News Agency/Henrik Montgomery via REUTERS

Students hold placards as they demonstrate to demand global action on climate change as part of the "Fridays for Future" movement in Riga, Latvia March 15, 2019. REUTERS/Ints Kalnins

Students hold banners and placards during a demonstration against climate change in New York, U.S., March 15, 2019. REUTERS/Shannon Stapleton

Demonstrators take part in a protest against climate change, organised by the YouthStrike4Climate movement, in Brighton, Britain March 15, 2019. REUTERS/Peter Nicholls

A child holds a banner during a protest against climate change in central Brussels, Belgium March 15, 2019. REUTERS/Yves Herman

A student holds a placard to support Swedish environmental campaigner Greta Thunberg during a strike from school to demand action on climate change at the town hall square of Duesseldorf, Germany, March 15, 2019. REUTERS/Wolfgang Rattay

Demonstrators take part in a protest against climate change, organised by the YouthStrike4Climate movement, in London, Britain March 15, 2019. REUTERS/Henry

Students demonstrate to demand global action on climate change as part of the "Fridays for Future" movement in Madrid, Spain, March 15, 2019.REUTERS/Susana Vera

Youth hold banners as they demonstrate for climate change during the "Fridays for Future" school strike, on Heldenplatz in Vienna, Austria March 15, 2019. REUTERS/Leonhard Foeger

Students strike for action on climate change in front of the government headquarters in Kiev, Ukraine March 15, 2019. REUTERS/Gleb Garanich

Demonstrators take part in a protest against climate change in central Brussels, Belgium March 15, 2019. REUTERS/Yves Herman Image used for illustrative purpose.

Participants hold banners and placards during a demonstration against climate change in Zurich, Switzerland March 15, 2019. REUTERS/Arnd Wiegmann