The world has warmed nearly 1.2C so far -- enough to usher in a crescendo of deadly heatwaves, floods and storm surges made worse by rising seas.
Current pledges registered under the 2015 treaty, if fulfilled, would still see temperatures rising a catastrophic 2.8C, potentially triggering runaway warming, where natural processes would add massive amounts of carbon into the atmosphere.
The G20 accounts for three-quarters of all human-caused emissions, which means the planet's future is largely in its hands.
Two G20 nations -- India and Turkey -- have failed to update their original carbon cutting plans submitted in 2015, as required under the Paris Agreement.
Neither has non-G20 member Egypt, which will host the COP27 climate summit in November.
Australia, Brazil, Indonesia and Mexico submitted revised 2030 targets that did nothing to further reduce emissions, according to the joint analysis from the World Resources Institute, the Energy and Climate Intelligence Unit and the E3G non-profit groups.
Now or never
Russia, Saudi Arabia and China -- which accounted for a third of global emissions last year -- did offer enhanced plans, "but there is still considerable scope to improve their commitments this year beyond their current policies," the report concluded.
The remaining G20 countries, including the United States and major European economies, raised their ambitions in 2021 but are still not on track to meet their earlier targets.
"None of the G20 are doing enough to keep hopes of limiting warming to 1.5C alive," said Tom Evans, a researcher at E3G.
"So far this year, they seem to have completely forgotten the promise they made at COP26 just six months ago to strengthen their 2030 climate targets."
A rapid rise in fossil fuel prices following Russia's invasion of Ukraine coupled with the declining cost of renewables could help speed the shift away from carbon-intensive energy, the report said.
And on the sidelines of the UN climate talks in Glasgow, many nations made pledges to halt forest loss by 2030, cut methane emissions, end financing for fossil fuels, and hasten the phase-out of coal use.
Combined, these voluntary measures could potentially help cap global temperature rise at 2C, according to peer-reviewed studies.
But all fall outside international mechanisms for measuring and verifying compliance.
"It is now or never if we want to limit global warming to 1.5C," said Jim Skea, co-chair of a landmark IPCC report which set out options for slashing greenhouse gas emissions last month.
"Without immediate and deep emissions reductions across all sectors, it will be impossible."