IPCC report warns greenhouse gas levels at highest point in 800,000 years

The world's top scientists have given their clearest warning yet of the severe and irreversible impacts of climate change.

The United Nations Intergovernmental Panel on Climate Change (IPCC) has released its synthesis report, a summary of its last three reports.

It warns greenhouse gas levels are at their highest they have been in 800,000 years, with recent increases mostly due to the burning of fossil fuels.

"Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems," the report said.

"Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks."

IPCC chairman Rajendra Pachauri said the comprehensive report brings together "all the pieces of the puzzle" in climate research and predictions.

"It's not discrete, and [highlights] distinct elements of climate change that people have to deal with, but [also] how you might be able to deal with this problem on a comprehensive basis by understanding how these pieces of the puzzle actually come together," Dr Pachauri said.

The report reiterates that the planet is unequivocally warming, that burning fossil fuels is significantly increasing greenhouse gas emissions and the effects of climate change - like sea level rises - are already being felt.

IPCC vice-chair Jean-Pascale van Ypersele said while Mr Abbott was correct to point out the world could not end its reliance on fossil fuels for energy immediately, change was necessary.

"The continued usage of fossil fuel could damage not only the environment but more substantially even the habitability of the planet and could erode the possibility to keep this planet habitable," he said.

"He's right, but the IPCC is right as well, and this is why climate negotiations, where the different bits of information including about the importance of energy in development, need to be taken into account and that's also why the climate negotiations are so difficult.

"Energy is important for development but clean energy is important for protecting [the] climate."

Environment Minister Greg Hunt said the Government's Emissions Reduction Fund - part of its Direct Action climate change policy which passed the Senate last week - will ensure power stations are cleaner.