Two international bodies say the world needs to swiftly shift energy production away from fossil fuels if it is to prevent a dangerous increase in global temperatures.
In separate reports, the International Energy Agency and the International Renewable Energy Agency conclude that fundamentally changing the way power is produced would require considerable investment - though there were would also be big savings and many new jobs.
The reports, released on Monday ahead of a meeting on energy and climate change in Berlin, differ in the extent to which fossil fuels can remain part of the mix if global average temperatures increases are to stay below 2C, compared with pre-industrial times.
President Donald Trump has pledged to roll back climate commitments made by the previous US administration.
To ensure a two-thirds chance of the temperature target, the IEA said, "would require an unparalleled ramp up of all low-carbon technologies in all countries."
Ambitious measures would include "the rapid phase-out of fossil fuel subsidies, CO2 prices rising to unprecedented levels, extensive energy market reforms, and stringent low-carbon and energy efficiency mandates would be needed to achieve this transition," it said.
"Such policies would need to be introduced immediately and comprehensively across all countries," the IEA added.
The IRENA report concludes that "early action is critical" and failure to act swiftly will only increase costs further down the line.
The IRENA scenario also predicts that more jobs will be created than lost.