European Council President Donald Tusk arrives for the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Leonhard Foeger

The John Amos coal-fired power plant is seen behind a home in Poca, West Virginia May 18, 2014. REUTERS/Robert Galbraith/File Photo

Coal is transported via conveyor belt to the coal-fired Jim Bridger Power Plant that supplied by the neighboring Jim Bridger mine that is owned by energy firm PacifiCorp and the Idaho Power Company, outside Point of the Rocks, Wyoming March 14, 2014. REUTERS/Jim Urquhart/File Photo

Austrian presidential candidate Alexander Van der Bellen, who is supported by the Greens, addresses a news conference in Vienna, Austria, September 12, 2016. REUTERS/Leonhard Foeger

A Union flag flies next to the flag of the European Union in Westminster, London, Britain June 24, 2016. REUTERS/Toby Melville/File Photo

United States one dollar bills are seen on a light table at the Bureau of Engraving and Printing in Washington November 14, 2014. REUTERS/Gary Cameron/File Photo

An Iranian flag flutters in front of the International Atomic Energy Agency (IAEA) headquarters in Vienna, Austria, January 15, 2016. REUTERS/Leonhard Foeger

New Jersey Governor Chris Christie speaks at the Republican National Convention in Cleveland, Ohio, U.S. July 19, 2016. REUTERS/Jim Young