Leaders of the Group of 20 major economies will say they aim to cap global warming at the 1.5 degrees Celsius level but largely avoid firm commitments, according to a draft joint statement seen by Reuters.
1.5 degrees is the level scientists say is vital to avoid disaster, but some of the world's biggest polluters have still not committed to it.
G20 leaders gathered on Saturday (October 30) for a two-day summit in Rome.
But the 5th draft of their joint statement shows tough negotiations on wording has in places only weakened it.
"Keeping 1.5°C within reach will require meaningful and effective actions by all countries," it says, where a previous draft called for "immediate action".
And the planned communique offers little detail on how countries will curb emissions.
It says leaders recognize the, quote, "key relevance" of achieving net zero carbon emissions by the middle of this century.
But China, the largest global emitter of greenhouse gases, has set a 2060 target date.
The role of the G20 - whose nations are responsible for an estimated 80% of global greenhouse gas emissions - is crucial ahead of the U.N.'s "COP26" climate summit - to be held in Glasgow, Scotland next week.
It includes a pledge to halt financing of overseas coal-fired power generation by the end of this year, and to, quote, "do our utmost" to stop building new coal power plants before the end of the 2030s.
Fossil fuel subsidies are to be phased out "over the medium term."
Leaders look likely to fall short of demands by developing countries on so-called "climate financing", where richer countries help poorer ones to finance their green transitions.
U.N. experts say that even if current national plans are fully implemented, the world is headed for global warming of 2.7 degrees, with a catastrophic acceleration of events such as drought, storms and flooding.