A bombshell climate science report "must sound a death knell" for coal, oil and gas, United Nations Secretary-General Antonio Guterres said Monday, warning that fossil fuels were destroying the planet.

The Intergovernmental Panel on Climate Change concluded that the 1.5C temperature goal of the Paris Agreement would likely be breached around 2030 -- a decade earlier than it itself projected just three years ago.

Guterres called the IPCC's assessment -- the most detailed review of climate science ever conducted -- "code red for humanity".

"This report must sound a death knell for coal and fossil fuels, before they destroy our planet," he said in a statement.

"Countries should also end all new fossil fuel exploration and production, and shift fossil fuel subsidies into renewable energy."

In its first major scientific assessment since 2014, the IPCC said that Earth's average surface temperature is projected to hit 1.5 or 1.6 degrees Celsius above preindustrial levels at around 2030, no matter what trajectory greenhouse gas emissions take in the meantime.

By mid-century, the 1.5C threshold will have been breached across the board, by a tenth of a degree along the most ambitious pathway, and by nearly a full degree at the opposite extreme.

'The alarm bells are deafening'

In his most frontal assault yet on the fossil fuel industry that powers the global economy, Guterres said "immediate action" was needed to decarbonise the energy sector.

"The alarm bells are deafening, and the evidence is irrefutable: greenhouse gas emissions from fossil fuel burning and deforestation are choking our planet and putting billions of people at immediate risk," said Guterres.

The Portuguese diplomat said keeping the 1.5C temperature goal in play meant that no new coal plants could be built and that all energy derived from burning coal must come from renewable sources by 2040.

Atmospheric levels of planet-warming CO2 are currently at their highest in at least the last two million years, with methane and nitrous oxide levels at their highest since 800,000 years ago.

Despite a record drop in carbon pollution last year driven by pandemic restrictions, the IPCC found "no detectable decrease" in the rate of greenhouse gas accumulation.

Guterres called on world leaders to ensure the COP26 climate summit in November leads to ramped up emissions cuts and finance to countries already dealing with the fallout from global heating.

"If we combine forces now, we can avert climate catastrophe," he said.

"But, as today's report makes clear, there is no time for delay and no room for excuses."