The legality of the Morrison government's planned use of an emissions reduction short cut to meet Australia's Paris targets could be open to challenge on several grounds, analysts say.

Separate analyses by the Australia Institute and Climate Analytics, and by the federal Greens, argue the government's intention to use so-called "Kyoto carry-over credits" to count against the country's Paris climate pledges is flawed and should be rejected by other nations.

Emissions Reduction Minister Angus Taylor, left, at the Madrid COP 25 with acting Spanish Economy Minister Nadia Calvino and Werner Hoyer, president of the European Investment Bank. Credit:EPA/Juan Carlos Hidalgo

They say that as the Kyoto and Paris climate deals were separate agreements, there is no provision for previous "overachievement" in one period to be counted in subsequent periods.

The reports come as Australia's delegation led by Energy and Emissions Reduction Minister Angus Taylor is in the midst of climate negotiations at a global summit in Madrid. A draft version of one section up for debate contains a clause specifically ruling out the use of Kyoto credits to meet Paris targets.