The only three living diplomats who have led the United Nations global warming talks said there’s little chance the next climate treaty will prevent the world from overheating. The specific goal, to hold temperature increases to 2 degrees Celsius (3.6 degrees Fahrenheit), was endorsed by envoys from 190 nations in 2010. It’s considered the maximum the environment can bear before climate change becomes more dangerous. Delegates to the UN Framework Convention on Climate Change meet in Warsaw starting Nov. 11 to work on a treaty that could be agreed to in 2015. The comments from the current and former executive secretaries to the UNFCCC add to the urgency of the Warsaw talks. Humans already have emitted more than half the greenhouse gases needed to surpass the 2-degree target, a panel of scientists brought together by the UN concluded in September.