( CNN ) What President Barack Obama described as the greatest threat to future generations was neither terrorism nor ISIS . It was n't nuclear weapons in rogue states either . `` No challenge poses a greater threat to future generations than climate change , '' said Obama in his State of the Union speech Tuesday . His statement was met with scattered , muted applause . The United States should lead in international efforts to protect `` the one planet we 've got , '' he said . 2014 was the warmest year since record keeping began . `` One year does n't make a trend , '' he said . `` But this does -- 14 of the 15 warmest years on record have all fallen in the first 15 years of this century . '' But American commitment to reduce greenhouse gas emissions and curb global warming has been intermittent throughout the years . The United States did not ratify the Kyoto Protocol , a binding agreement in 1997 to cut greenhouse gas emissions . A 2007 U.N. climate change conference ended with anger at the United States , then under the Bush administration , when it balked at binding carbon cuts . `` We were used to having U.S. as a pariah , '' said Liz Gallagher , the program leader of climate diplomacy at E3G , an environmental group . Environmentalist noted a shift in recent years under Obama , including a recent agreement with China to reduce emissions . `` It 's better to have America inside the game than outside . It makes it easier to persuade everyone else , '' said Gallagher . Critical year for climate change policy . The U.S. remains the second greatest polluter , behind China . In a historic climate change deal in November , Obama and Chinese President Xi Jinping announced that both countries would curb their greenhouse gas emissions over the next two decades . The two countries account for over one third of global greenhouse gas emissions . `` Because the world 's two largest economies came together , other nations are now stepping up , and offering hope that , this year , the world will finally reach an agreement to protect the one planet we 've got , '' Obama said during his speech . A critical UN Climate Change Conference will be held in Paris in December this year , aimed at reaching a legally-binding , international climate agreement . `` This is a pivotal year for advancing the climate effort both at home and internationally , and the president 's continued leadership is essential on both fronts , '' said Bob Perciasepe , president of the Center for Climate and Energy Solutions . Climate change disproportionately affects the most impoverished . Rising sea levels , threatened water and food supply devastate people 's lives . A U.N. Intergovernmental Panel on Climate Change warned in a report that the effects of climate change could cost governments around the world more than $ 100 billion a year . Warming and warning . Since 1880 , the Earth 's average surface temperature has warmed by about 1.4 degrees Fahrenheit ( 0.8 degrees Celsius ) , according to NASA scientists . Most of the warming has occurred in the past three decades . `` The best scientists in the world are all telling us that our activities are changing the climate , and if we do not act forcefully , we 'll continue to see rising oceans , longer , hotter heat waves , dangerous droughts and floods , and massive disruptions that can trigger greater migration , conflict , and hunger around the globe , '' Obama said . `` The Pentagon says that climate change poses immediate risks to our national security . We should act like it . ''
Obama met with scattered applause when he calls climate change greatest threat to future generations . China and U.S. are leading polluters in the world . Comment: