Global warming of 1.5 degrees Celsius to 2 degrees Celsisus will be exceeded before the end of the century unless humans make deep reductions in carbon dioxide and other greenhouse gas emissions within decades, UN scientists said in a new study.

The UN's Intergovernmental Panel on Climate Change (IPCC) sounded a dire warning Monday, saying the world is dangerously close to runaway warming – and that humans are "unequivocally" to blame.

Already, greenhouse gas levels in the atmosphere are high enough to guarantee climate disruption for decades if not centuries, the IPCC