16-year-old Swedish Climate activist Greta Thunberg speaks at the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Carlo Allegri TPX IMAGES OF THE DAY

U.S. President Donald Trump checks his watch as he attends the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Jonathan Ernst

Swedish environmental activist Greta Thunberg watches as U.S. President Donald Trump enters the United Nations to speak with reporters in a still image from video taken in New York City, U.S. September 23, 2019. REUTERS/Andrew Hofstetter TPX IMAGES OF THE DAY

Video segments play during the opening ceremony of the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Lucas Jackson

U.S. President Donald Trump and Vice President Mike Pence attend the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Carlo Allegri

German Chancellor Angela Merkel speaks during the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Lucas Jackson

French President Emmanuel Macron speaks during the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Carlo Allegri

New Zealand's Prime Minister Ms. Jacinda Ardern speaks during the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Carlo Allegri

India's Prime Minister Narendra Modi speaks during the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Carlo Allegri

Pakistan's Prime Minister Imran Khan speaks next to Norway's Prime Minister Erna Solberg during the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Lucas Jackson

Climate change activists block traffic at an intersection near the White House in Washington, U.S. September 23, 2019. REUTERS/Erin Scott

German Chancellor Angela Merkel speaks during the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Lucas Jackson

German Chancellor Angela Merkel (C) attends the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Carlo Allegri

Activist Alexandria Villasenor listens with other child petitioners from twelve countries around the world who presented a landmark complaint to the United Nations Committee on the Rights of the Child to protest the lack of government action on the climate crisis during a press conference in New York, U.S., September 23, 2019. REUTERS/Shannon Stapleton

U.S. President Donald Trump departs after attending the 2019 United Nations Climate Action Summit at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Lucas Jackson

Climate change activists march down Connecticut Avenue in Washington, U.S. September 23, 2019. REUTERS/Erin Scott

A man reads a flyer as mother with prams protest outside BP's global headquarters, ahead of the UN Climate Action Summit, in London, Britain September 23, 2019. REUTERS/Henry Nicholls

Environmental activists block traffic as part of "Shut Down DC" protests seeking to pressure U.S. politicians to fight climate change in Washington, U.S., September 23, 2019. REUTERS/Kevin Lamarque

Mothers with prams protest outside Shell's UK headquarters, ahead of the UN Climate Action Summit, in London, Britain September 23, 2019. REUTERS/Henry Nicholls

Police work to remove protesters from a boat being used to block traffic at an intersection near the White House in Washington, U.S. September 23, 2019. REUTERS/Erin Scott

Climate change activists block traffic at an intersection near the White House in Washington, U.S. September 23, 2019. REUTERS/Erin Scott

Climate change activists block early morning rush hour traffic, standing in the intersection of 14th Street and Independence Avenue in Southwest Washington, as demonstrators block key buildings and roads to stop "business-as-usual" in the U.S. capital and demand action by U.S. politicians on climate change in Washington, U.S., September 23, 2019. REUTERS/Michael A. McCoy

Environmental activists block traffic as part of protests seeking to pressure U.S. politicians to fight climate change in Washington, U.S., September 23, 2019. REUTERS/Kevin Lamarque

Climate change activists block traffic at an intersection near the White House in Washington, U.S. September 23, 2019. REUTERS/Erin Scott