A view of the opening of COP21 on climate change Monday in Paris. More than 150 world leaders are meeting for the 21st Session of the Conference of Parties to the United Nations Framework Convention on Climate Change. Patrick Aventurier/Getty Images hide caption
Climate scientists who scrutinized the U.N. accord are urging citizens to keep a sharp eye on each nation's leaders to make sure they follow through on pledges to reduce emissions. Simone Golob/Corbis hide caption
Sen. Ted Cruz, R-Texas, leads the Subcommittee on Space, Science and Competitiveness during a hearing on climate change on Tuesday. Saul Loeb/AFP/Getty Images hide caption
Tony de Brum, the foreign minister of the Marshall Islands, relaxes at the Majuro Atoll last month. Climate change poses an existential threat to places like the Marshall Islands, which rise no higher than 6 feet above sea level in most places. De Brum is representing the Marshall Islands at the climate talks in Paris. Rob Griffith/AP hide caption
President Obama addresses the opening ceremony of the World Climate Change Conference 2015 (COP21) on Nov. 30. Jim Watson/AFP/Getty Images hide caption
A coal mound stands outside a Kentucky Utilities Co. station. Bloomberg/Bloomberg via Getty Images hide caption
Young boys in Beijing check a smartphone in front of their home near a coal-fired power plant. As China's economy slowed in 2015, its industrial use of coal likely dropped, too, researchers say. That may be behind the slight drop in global CO2 emissions. Kevin Frayer/Getty Images hide caption
Las Cañadas is an ecological cooperative in Veracruz, Mexico that's working to sequester carbon and mitigate climate change while producing food, materials, chemicals and energy. Courtesy of Ricardo Romero/Chelsea Green Publishing hide caption
A Pakistani boy peers out from behind a mosquito net after his family fled their home due to catastrophic flooding in Sindh province. Muhammed Muheisen/AP hide caption
U.S. Rep. Lamar Smith, R-Texas, and Kathryn Sullivan, director of the National Oceanic and Atmospheric Administration, have been tangling for months over the legitimacy of a climate study NOAA scientists published in Science. Drew Angerer/AP; Mark Wilson/Getty Images hide caption
Representatives of 195 nations have adopted a blueprint to address climate change at the COP21 conference. Last night, Leonardo DiCaprio spoke to mayors attending the talks in Paris about pushing for local actions to fight climate change. Francois Mori/AP hide caption
Bangladesh is facing drought, cyclones and floods. This expanse of water, photographed in September 2014, was a field the month before. It's in the Kalashuna village in Gaibandha district. Allison Joyce/Getty Images hide caption
A piece of ice floats in Los Glaciares National Park in Santa Cruz province, Argentina. Mario Tama/Getty Images hide caption
President Obama attended the plenary session of the international climate conference Monday, just outside Paris. By using regulations instead of treaties, Obama hopes to continue to cut U.S. emissions of greenhouse gases. Eric Feferberg/AFP/Getty Images hide caption
This sea wall protects the Quinault Indian Nation at the mouth of the Quinault River. In March, a state of emergency was declared by the tribe when waves crashed over the wall. Larry Workman/KUOW/EarthFix hide caption
A conference attendee looks at a projection of the Earth on Monday, the opening day of the COP 21 United Nations conference on climate change, in Le Bourget, on the outskirts of Paris. Alain Jocard/AFP/Getty Images hide caption
Coal miner Dennis Ferrell watches over conveyer belts carrying coal out of a mine in Welch, W.Va. Climate talks in Paris are focused on moving away from coal in hopes of protecting the environment. David Goldman/AP hide caption
President Obama listens to Turkish President Recep Tayyip Erdogan during a bilateral meeting in Tuesday in Paris. Evan Vucci/AP hide caption
Cocoa pods in Ivory Coast, one of the world's top producers of cocoa. Climate models suggest that West Africa, where much of the world's cocoa is grown, will get drier, which could affect supply. Issouf Sanogo/AFP/Getty Images hide caption
Climate models project 21st century global temperatures. NASA's Scientific Visualization Studio and NASA Center for Climate Simulation hide caption
President Obama (from left), French President Francois Hollande and Microsoft co-founder Bill Gates applaud a speech during the Mission Innovation event at the UN conference on climate change Monday in Paris. Jim Watson/AFP/Getty Images hide caption
A man walks through hundreds of pairs of shoes displayed in Paris as part of a rally called "Paris sets off for climate" on Sunday, Nov. 29. More than 140 world leaders are gathering around Paris for high-stakes climate talks this week. Laurent Cipriani/AP hide caption