"The New York Times" and others reported in 2015 that oil companies knew that burning oil and gas could cause climate change and global warming since the 1970s but nonetheless funded deniers for years. Dana Nuccitelli wrote in "The Guardian" that a small fringe group of climate deniers were no longer taken seriously at the 2015 United Nations Climate Change Conference, in an agreement that "we need to stop delaying and start getting serious about preventing a climate crisis." However, "The New York Times" says any implementation is voluntary and will depend on any future world leaders—and every Republican U.S. presidential candidate in 2016 questioned or denied the science of climate change.