A new draft of a United Nations report warns climate change could become “irreversible” if greenhouse gas emissions go unchecked. The report from the Intergovernmental Panel on Climate Change, obtained by media outlets, says human-driven warming has already fueled extreme heat and rains, as temperatures have risen 1.5 degrees Fahrenheit since pre-industrial times. While the report says it could still be possible to cap warming at the globally agreed-upon limit of 3.6 degrees Fahrenheit, it warns a continued rise in emissions could eventually cause an eight-degree Fahrenheit rise, prompting mass extinction of plants and animals and catastrophic floods. If global warming is to be adequately contained, the report says, at least three-quarters of known fossil fuel reserves must remain in the ground.