G20 leaders agreed Sunday on the need to keep global warming to 1.5 degrees Celsius but fell short of a hoped-for pledge on reaching net zero emissions, according to a draft communique seen by AFP.

The G20 economies emit nearly 80 percent of carbon emissions, and are under pressure to go bold on climate to give a much-needed boost to crucial UN climate talks starting in Glasgow on Sunday.

According to the draft, which sources said would be the final one, the G20 reaffirm their support for the 2015 Paris Agreement goal of keeping "the global average temperature increase well below 2 degrees and to pursue efforts to limit it to 1.5 degrees above pre-industrial levels."

In addition, they state that "keeping 1.5 degrees within reach will require meaningful and effective actions and commitment by all countries."

This will "require taking into account different approaches, through the development of clear national pathways that align long-term ambition with short- and medium-term goals, and with international cooperation and support."

Experts say meeting the 1.5 degree target means slashing global emissions nearly in half by 2030 and to "net-zero" by 2050.

But the draft declaration, due to be published later Sunday, does not set a clear deadline for carbon net neutrality, saying it should be achieved "by or around mid century."

The declaration includes a commitment to "put an end to the provision of international public finance for new unabated coal power generation abroad by the end of 2021," a key pledge that mirrors what was already promised by China in September.

Elsewhere, it reaffirms the so-far unmet commitment by developed countries to mobilize $100 billion for developing countries for climate adaptation costs.