If global fossil fuel emissions are not cut by 7.6 per cent annually over the next ten years the world will miss its chance to avert climate disaster, the United Nations said in its annual report on greenhouse gases.
The UN found that even taking into account the Paris agreement, where nations committed to limit temperature rises above pre-industrial levels to "well below" 2C, and to a safer 1.5-C if at all possible, the world is on track for a 3.2C temperature rise.
Scientists fear that could tear at the fabric of society.
Emissions have risen on average by 1.5 per cent annually over the last decade, hitting a record 55.3 billion tonnes of carbon dioxide or equivalent greenhouse gases in 2018 — three years after 195 countries signed the Paris treaty on climate change.
The World Meterological Organization said on Monday that atmospheric greenhouse gas concentrations hit an all-time record in 2018.
The UN assessment is "bleak" — even if every country made good on its Paris pledges, Earth's "carbon budget" for a 1.5-C rise -- the amount we can emit to stay below a certain temperature threshold -- would be exhausted within a decade.
While it insisted the 1.5C goal is still attainable, it acknowledged that this would require an unprecedented, co-ordinated upheaval of a global economy that is still fuelled overwhelmingly by oil- and gas-fuelled growth.
The Emissions Gap report, now in its tenth year, also details the cost of a decade of government inaction.
Had serious climate action begun in 2010, just after the Copenhagen summit that breathed new life into the debate, annual needed emissions cuts would be 0.7 per cent for 2C of warming and 3.3 per cent for 1.5C.
The report highlighted specific "opportunities" for big emitters to push their economies into line with the Paris goals.
While advice varies between countries, the theme is clear: completely phase out coal, significantly pare back oil and gas, and dramatically build up renewable energy.
G20 nations were singled out as laggards: although they produce around 78 per cent of all emissions, only 15 rich nations have outlined plans to reach net-zero.
In all, countries must increase their contributions to the climate fight five-fold to deliver the cuts needed for 1.5C.
"Incremental changes will simply not make it," said lead author John Christensen.
"We really need to transform societies in these 10 years."
Last year the Intergovernmental Panel on Climate Change — the world's leading scientific body on the subject — issued a stark warning that going beyond 1.5C would increase the frequency and intensity of heatwaves, superstorms and mass flooding.
With just 1C of warming so far, 2019 is projected to be the second hottest in human history, a year marred by deadly wildfires and cyclones rendered more frequent as temperatures climb.
And despite the need for urgent action, with global energy demand set to continue rising for years, the UN itself conceded Tuesday that "there is no sign of (greenhouse) gas emissions peaking in the next few years".
The report said emissions would need to drop 55 per cent by 2030 to stay on a 1.5C track — an unprecedented fall at a time of sustained global growth.