Climate change and Covid are top of the agenda of leaders from the world's major economies meeting in Italy.
It is the first time the G20 leaders are meeting face-to-face since the start of the pandemic.
However, China's Xi Jinping and Russia's Vladimir Putin are not in Rome for the summit, choosing to appear via video link instead.
The talks come amid increasingly dire warnings for the future if urgent action is not taken to cut emissions.
The G20 group - made up of 19 countries and the European Union - is estimated to account for 80% of the world's carbon dioxide emissions.
Speaking to the BBC, UK Prime Minister Boris Johnson described climate change as "the biggest threat to humanity", saying it posed a "risk to civilisation basically going backwards".
However, he acknowledged that neither the G20 meeting, nor the COP26 summit in Glasgow which begins on Monday, would halt global warming, but could, if the right measures were taken, "restrict the growth in the temperature of the planet".
According to Reuters news agency, a draft communiqué outlines a promise from the G20 to work towards limiting the rise in temperatures to 1.5C (2.7F), saying it "will require meaningful and effective actions by all countries".
The draft also notes the need for "developed countries to mobilise $100bn (£73bn) annually from public and private sources through to 2025 to address the needs of developing countries" so they can tackle climate change - a promise richer countries have failed to keep since 2009, when it was initially pledged.
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