ADP Co-chairs Daniel Reifsnyder (left) and Ahmed Djoghlaf (center) say their negotiation work is difficult but worth it. "We only have one planet, you know," Reifsnyder says. "We have to protect it." Courtesy of IISD/ENB hide caption

itoggle caption Courtesy of IISD/ENB

Ismael Medjdoub grew up in one of Paris' banlieues. He spends up to two hours a day commuting from his home in Tremblay en France to work and to school at the prestigious Sorbonne in Paris. Bilal Qureshi/NPR hide caption

itoggle caption Bilal Qureshi/NPR

A drone is displayed Wednesday at Paris store Azur Modelisme. Law enforcement officials in the city are concerned about recent unexplained drone fly-bys of high-security sites, including the Eiffel Tower and the U.S. embassy. Eleanor Beardsley/NPR hide caption

itoggle caption Eleanor Beardsley/NPR

French Ambassador to the U.S. Gerard Araud addresses a solidarity gathering at the Adas Israel Congregation in Washington, D.C., on Wednesday. Araud said last week's attack was "in a sense maybe worse than what we were expecting, because it was done in a very professional way." Nicholas Kamm/AFP/Getty Images hide caption

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A man walks past a makeshift memorial for French Muslim policeman Ahmed Merabet near the site where he was shot dead by gunmen, close to the headquarters of the French satirical weekly Charlie Hebdo. Joel Saget/AFP/Getty Images hide caption

itoggle caption Joel Saget/AFP/Getty Images

World leaders, including, from the left, Israel's Prime Minister Benjamin Netanyahu, Mali's Ibrahim Boubacar Keita, France's Francois Hollande, Germany's Angela Merkel, EU President Donald Tusk and Palestinian President Mahmoud Abbas march in Paris on Sunday to honor the victims of three days of bloodshed. A White House spokesman acknowledged "we should have sent someone with a higher profile." Philippe Wojazer/AP hide caption

itoggle caption Philippe Wojazer/AP

A man holds a pencil in the air during a minute of silence in Paris on Thursday for the cartoonists and other victims of gunmen on the offices of French satirical newspaper Charlie Hebdo. Matthieu Alexandre /AFP/Getty Images hide caption

itoggle caption Matthieu Alexandre /AFP/Getty Images

General Secretary of the Elysee Palace Jean-Pierre Jouyet, head bowed foreground at left, and the Elysee Palace staff observe a minute of silence on Thursday for victims of the shooting at the satirical newspaper Charlie Hebdo, in Paris on Wednesday. Philippe Wojazer/AP hide caption

itoggle caption Philippe Wojazer/AP

A police bulletin sought the public's help in finding two suspects in the deadly attack on a satirical magazine's Paris offices Wednesday. Pictured are brothers Chérif (left) and Said Kouachi. La prefecture de Police hide caption

itoggle caption La prefecture de Police

A police bulletin sought the public's help in finding two suspects in the deadly attack on a satirical magazine's Paris offices Wednesday. Pictured are brothers Cherif (left) and Said Kouachi. La prefecture de Police hide caption

itoggle caption La prefecture de Police