The world’s top climate scientists have unveiled their strongest warning to date about the disastrous consequences of human-caused climate change if drastic efforts are not adopted to slash greenhouse gas emissions. For the first time, the International Panel on Climate Change formally endorsed a limit on emissions, saying no more than one trillion tons of carbon can be burned if humanity hopes to avoid a global temperature increase of more than 3.6 degrees Fahrenheit. Already, more than half that amount has been emitted since the Industrial Revolution, and the world is on pace to burn its trillionth ton of carbon in less than three decades. The IPCC expressed even more certainty than ever before that humans are responsible for global warming, saying there is a 95 to 100 percent chance most warming in recent decades has been caused by humans.