The UN climate chief on Sunday called on governments to take bold steps to tame carbon emissions after a landmark report said the worldwide aim to limit global warming was still attainable.
"The world can still combat climate change but only if nations raise their collective ambition to achieve a carbon-neutral world in the second half of the century," said Christiana Figueres, executive secretary of the UN Framework Convention on Climate Change (UNFCCC).
"We cannot play a waiting game where we bet on future technological miracles to emerge and save the day."
Figueres oversees UN negotiations towards a global pact on curbing climate-altering greenhouse-gas emissions that must be agreed in Paris late next year.
Its goal is to limit warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels, but progress has been hampered by bickering over how to divide up the bill.
The report, issued in Berlin by the United Nations' Intergovernmental Panel on Climate Change (IPCC), said the challenge to curb warming to levels deemed relatively safe by scientists can still be met through a "large-scale" shift to greener energy.
There is a "likely" chance of meeting the target if the world cuts annual greenhouse gas emissions 40-70 per cent by 2050 from 2010, it said.
It would also entail a "tripling to nearly a quadrupling" in the share of energy from renewable and nuclear sources and from traditional fossil or new biofuel sources whose emissions are captured and locked away.
But the document, a summary for policymakers that government representatives scrutinised line-by-line in Berlin over six days from Monday, also warned that on present trends the planet would be 3.7-4.8 C warmer by 2100 -- a level scientists say could be catastrophic.
"This new report challenges decision makers by presenting to them alternative futures and spelling out the pathway to each," said Figueres, in a statement issued by the UNFCCC secretariat in Bonn.
"We already have the finance and proven technologies needed to do what is required now. The challenge and the opportunity is to increase the speed and scale of action."
She called for "bold policy incentives" to reduce emissions, and constructive negotiations towards the 2015 climate pact.
And she urged governments "to step forward this year with generous capital contributions" to help developing nations switch to cleaner energy to fuel their rise out of poverty.