Riot police fire tear gas during a protest by supporters of Dilma Rousseff in Sao Paulo, Brazil August 31, 2016. (Photo by Paulo Whitaker/Reuters)

In this Thursday, December 1, 2016 photo, Cat Bigney, part of the Oglala Native American tribe, waits on the shore of the Cannonball river for travelers to arrive by canoe at the Oceti Sakowin camp where people have gathered to protest the Dakota Access oil pipeline in Cannon Ball, N.D. So far, those at the camp have shrugged off the heavy snow, icy winds and frigid temperatures. But if they defy next week's government deadline to abandon the camp, demonstrators know the real deep freeze lies ahead. Life-threatening wind chills and towering snow drifts could mean the greatest challenge is simple survival. (Photo by David Goldman/AP Photo)

A woman covers her face as a fire burns in the middle of town during an anti-G20 protest on July 7, 2017 in Hamburg, Germany. Authorities are braced for large-scale and disruptive protests as Leaders of the G20 group of nations arrive in Hamburg for the July 7-8 G20 summit. (Photo by Leon Neal/Getty Images)

Egyptian riot police charge towards protesters near Egypt's Interior Ministry, as violent demonstrations continued into their second day on February 3, 2012 in central Cairo, Egypt. (Photo by Ed Giles/Getty Images)

An activist takes a selfie during a protest ahead of the 2015 Paris Climate Conference, in Paris, Sunday, November 29, 2015. More than 140 world leaders are gathering around Paris for high-stakes climate talks that start Monday, and activists are holding marches and protests around the world to urge them to reach a strong agreement to slow global warming. (Photo by Christophe Ena/AP Photo)

Men stand at the top of a traffic lights post as they attend a rally to protest against satirical cartoons of prophet Mohammad, in Grozny, Chechnya January 19, 2015. Tens of thousands of people staged the rally on Monday in Chechnya against French magazine Charlie Hebdo's cartoons of the prophet, which the predominantly Muslim region's leader denounced as “vulgar and immoral”. The posters read, “Mohammad”. (Photo by Eduard Korniyenko/Reuters)

Wounded Reuters photographer Gleb Garanich, who was injured by riot police, takes pictures as riot police block protesters during a scuffle at a demonstration in support of EU integration at Independence Square in Kiev November 30, 2013. Riot police in the Ukrainian capital Kiev used batons and stun grenades to disperse hundreds of pro-Europe protesters from the city's main Independence Square early on Saturday, witnesses said. (Photo by Reuters/Stringer)

Punk protest band p*ssy Riot member Maria Alyokhina is detained by police at a protest in central Moscow February 24, 2014. Russian riot police detained over a hundred protesters, including two members of p*ssy Riot, on Monday at a Moscow courthouse where seven opponents of President Vladimir Putin were jailed from two and a half to four years over a demonstration that turned violent. (Photo by Maxim Shemetov/Reuters)