Fresh from issuing its starkest-ever warning about the impacts of global warming on Earth's weather system, the Intergovernmental Panel on Climate Change (IPCC) will meet until Friday to vet the choices meant to inform policymakers.

A draft of the document, seen by AFP, suggests there is a 15-year window for affordable action to safely reach the UN's warming limit of two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial times.

The report, the product of four years' work by hundreds of experts, aims to provide governments with the latest science on climate change.

It is also designed to inform the struggling effort to forge a worldwide pact by next year to curb greenhouse gases and help poor countries cope with climate impacts.

"Preventing dangerous interference with the climate system entails mitigating climate change," said Ottmar Edenhofer, co-chairman of the panel's Working Group III, which compiled the report.

"On a transparent, scientific basis, our report provides an understanding of the available options to meet this challenge."

A Summary for Policymakers will be publicly released in the German capital on Sunday, and the full report - authored by scientists but not submitted to the IPCC plenary for scrutiny - will be released shortly afterwards.

A draft of the summary expresses no preferences for how to tame the problem, nor what a safe level of warming should be.

But it says the UN's 2 C target remains feasible if "all countries" act quickly to mitigate, or ease, carbon emissions.