The United Nations' expert panel on climate science will warn overnight of severe and irreversible changes to the world's weather, unless emissions of greenhouse gases are virtually eliminated by the end of the century.
Climate impacts such as melting Arctic sea ice and rising sea levels, are already happening and could become irreversible.
The IPCC Synthesis Report will summarise the causes and impacts of - and solutions to - rising temperatures.
But the BBC reports there are concerns that political battles could neuter the final summary.
Over the past 13 months, the IPCC has released three major reports on the physical science, the impacts and the potential methods of dealing with climate change.
On Sunday they will release the Synthesis Report. This new study is meant to take the most important elements of all three and blend them into something new. It is not meant to be a cut-and-paste exercise.
They are likely to reiterate that warming is real and mainly caused by humans, they will say that without action there will be significant impacts on people, offal production and on the survival of species.
To prevent these scenarios the scientists are likely to say that there is no future for coal and oil without technology to capture CO2. One implication would be that 80 percent of the world's electricity should come from low carbon sources by 2050.