Former U.S vice president and climate activist Al Gore makes a speech on acting for climate to participants in a U.N. climate summit that is to work out ways of keeping global warming in check, in Katowice, Poland, Wednesday, Dec. 12, 2018.(AP Photo/Czarek Sokolowski)

A South Korean army soldier stands guard at the South's dismantled guard post inside the Demilitarized Zone (DMZ) in the central section of the inter-Korean border in Cheorwon, Dec. 12, 2018. Dozens of South Korean soldiers visited former front-line North Korean guard posts on Wednesday to verify their recent removal as part of warming diplomacy by the rival Koreas while U.S.-North Korea nuclear disarmament efforts remain stalled. (AP Photo/Ahn Young-joon, Pool)

Poland's Environment Minister Henryk Kowalczyk talks of the efforts that Poland is taking to limit its greenhouse gas emissions during a session of U.N. climate summit in Katowice, Poland, Tuesday, Dec. 11, 2018. (AP Photo/Czarek Sokolowski)

The lit up words "Peoples Vote", which calls for another referendum on Britain's European Union membership, are photographed by a remain, anti-Brexit supporter wearing a European flag design beret across the street from the Houses of Parliament in London, Monday, Dec. 10, 2018. British Prime Minister Theresa May has postponed Parliament's vote on her European Union divorce deal to avoid a shattering defeat — a decision that throws her Brexit plans into chaos. (AP Photo/Matt Dunham)

Swedish young activist, 15-year-old Greta Thunberg, right, speaks to climate activists during the March for Climate in a protest against global warming in Katowice, Poland, Saturday, Dec. 8, 2018, as the COP24 UN Climate Change Conference takes place in the city. (AP Photo/Alik Keplicz)

North Korean Foreign Minister Ri Yong Ho, left meets China's Foreign Minister Wang Yi at the Diaoyutai State Guesthouse in Beijing Friday, Dec. 7, 2018. (Fred Dufour/Pool Photo via AP)

FILE - In this Sept. 18, 2018, file photo, South Korean President Moon Jae-in, left, and North Korean leader Kim Jong Un ride in a car during a parade through a street in Pyongyang, North Korea. Day after day, rampant speculation about North Korean leader Kim’s possible trip to Seoul is making headlines in South Korea, despite no official confirmation from both Koreas. Many analysts say it would be virtually impossible for Kim to fulfill his reported promise to become the first North Korean ruler to visit South Korea by the end of this year, given stalemated nuclear diplomacy. But others say we never know until this year is over. (Pyongyang Press Corps Pool via AP, File)

Smoke rise from a waste incinerator in Paris, France, Tuesday, Dec. 4, 2018. The COP24 summit on climate change is taking place in Poland's southern city of Katowice from December 2 to 14, 2018. (AP Photo/Francois Mori)

U.S. President Donald Trump, left, and Russian President Vladimir Putin shake hands at the beginning of a meeting at the Presidential Palace in Helsinki, Finland, on July 16, 2018. (AP Photo/Pablo Martinez Monsivais)

Actor Arnold Schwarzenegger delivers a speech during the opening of COP24 UN Climate Change Conference 2018 in Katowice, Poland, Monday, Dec. 3, 2018.(AP Photo/Czarek Sokolowski)