Yale Environment 360: Saying it is 95 percent certain that humans have caused most of the global warming of the last half-century, scientists with the Intergovernmental Panel on Climate Change (IPCC) warned today that the world can afford to burn about 1 trillion more tons of carbon before facing extreme climate change. The IPCCs working group on the physical sciences for the first time set an upper limit on CO2 emissions, contending that humanity can combust only one-third of the 3 trillion tons of fossil fuels that...