If every single country were to follow through on its stated plans (a big if) then global greenhouse gas emissions would be 2 percent to 9 percent lower at the end of the decade than they are today.

But that would still put Earth on track to heat up roughly 2.5 to 2.9 degrees Celsius over preindustrial levels by the century’s end, the report found. With every fraction of a degree of warming, the risks from deadly heat waves, wildfires, droughts, storms and species extinctions increase significantly, scientists have said.