The Morrison government will be breaking international law and acting immorally if it uses Kyoto carryover credits to help it meet its 2030 emissions targets, says the chief architect of the landmark 2015 Paris Agreement.

Christiana Figueres, who was executive secretary of the United Nations Framework Convention on Climate Change from 2010 to 2016, said Australia's overachievement of its targets under the Kyoto Protocol was irrelevant to its Paris commitments, and attempting to use the credits from that overachievement would be "cheating" .