SAPPORO, Japan (AP) — So much has been invested in clean energy that there can be no rolling back of moves to end carbon emissions, U.S. climate envoy John Kerry said Sunday.

Kerry noted that if countries deliver on promises to phase out polluting fossil fuels, the world can limit average global warming to 1.7 degrees Celsius (2.7 degrees Fahrenheit), better than the worst case scenarios but still above the current limit of 1.5 C global warming above pre-industrial levels.