A new global pact to tackle climate change, agreed in Paris in December, could come into force two years earlier than the planned date of 2020, according to the UN climate chief.
"I think we will have a Paris agreement in effect in 2018," predicts Christiana Figueres, executive secretary of the United Nations Framework Convention on Climate Change.
The agreement, originally slated to take effect in 2020, will come into force once 55 countries representing 55 per cent of the world's total emissions have both signed and ratified it.
On April 22, at least 130 countries are expected to ink the agreement in New York, on the first day it opens for signature -- more than the 119 who signed the Law of the Sea, says Ms Figueres.
Getting the deal agreed and ratified, however, is just a prelude to the far more complicated work of switching the world's energy systems over to clean power and ramping up low-carbon infrastructure, she says.
That will take rapid and massive investment on a scale not seen since rebuilding after World War II, to make the changes needed quickly enough.
"We are two minutes to midnight on climate change. If you ask me, the Paris agreement is 10 years too late," says Ms Figueres.
Delays in negotiating the pact -- which sets a goal of keeping global average temperature rise to "well below" 2 degrees Celsius -- have put "an incredible amount of pressure" on efforts to revamp the world's systems, she adds.