Australia’s plan to use an accounting loophole to meet its commitment under the Paris climate agreement has no legal basis and suggests it has reneged on a pledge to make deeper emissions cuts once a global deal was reached, a new report says.

An analysis by Climate Analytics, a Berlin-based science and policy institute, found there were no grounds for Australia to claim credit towards its Paris emissions target for having beaten targets under its predecessor, the Kyoto protocol.

It found the two agreements were separate treaties and should not be treated as a continuation of one agreement.

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The report, commissioned by the Australia Institute, has been released as Australia faces a challenge from at least 100 mostly developing countries at a UN climate conference in Madrid over its plan to use carryover credits from the Kyoto protocol to meet its Paris target for 2030.

The analysis was backed at the conference by Anote Tong, a former president of low-lying Kiribati. Launching the report, he said if Australia had beaten its earlier targets it had the capacity to do more, not less.

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“Australia is on fire due in large part to climate change, ands it is beyond me why the Australian government is looking for ways to weaken the Paris agreement so it and others can do less to solve the climate crisis,” Tong said.

“This is about the real impact of what we are all trying to achieve here. Are we trying to work together or are we just shifting numbers?”

Carryover credits were allowed under the soon-to-be-obsolete Kyoto protocol in a bid to encourage countries to be as ambitious in cutting pollution as possible. They were not mentioned in the original Paris agreement but have been added to the text being negotiated in Madrid, with some countries proposing they be banned.

Officials told Senate estimates earlier this year that Australia was the only country planning to use them. Several developed countries have explicitly ruled out using them. Australia strongly opposes a ban and has factored in the credits as necessary for it to meet its Paris commitment.

Climate Analytics found there was nothing in the legal framework of the Kyoto protocol that permitted the carryover over of emissions cuts into a new agreement after it ends in 2020.

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It says most of the credits, which the Morrison government now describes as its “overachievement”, were a direct result of Australia having massive emissions from deforestation in 1990, the year against which targets under the Kyoto deal are measured.

According to the latest greenhouse accounts, deforestation made up about 30% of national emissions in 1990. It declined significantly in the years that followed, allowing Australia to increase fossil fuel emissions and still beat its first Kyoto target. This became known as the “Australia clause” of the Kyoto protocol, which was agreed by the Howard government in 1997.

The report says it would be perverse for Australia to be rewarded in 2030 for the existence of large-scale deforestation four decades earlier.

It says the claimed overachievement also came directly from Australia’s decision to give itself targets that were far less ambitious than other countries: an 8% increase in emissions between 1990 and 2010, and what was equivalent to just a 0.5% cut below 1990 and 2020 (expressed as a 5% cut below 2000 levels).

It says Australia’s attempt to minimise how much it had to cut emissions over the next decade was at odds with the goals and principles of the Paris agreement, committed countries to escalating action that reflected their “highest possible ambition”.

Including carryover credits effectively cuts Australia’s 2030 target in half, from a minimum 26% cut to less than a 14% cut. Pollution from transport and industry and fugitive emissions from fossil fuel excavation continue to rise. Government advisers recommended a minimum 45% cut.

Richie Merzian, the Australia Institute’s climate and energy director, said: “This research makes clear that there is no scientific, moral or legal foundation for the Australian government’s determination to gain credit for its historic recalcitrance.”

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The report says Australia appeared to have reneged on a commitment to increase its 2020 target from a 5% cut below 2000 levels to a 15% cut if the world reached a comprehensive treaty that was capable of limiting emissions to below 450 parts per million of atmospheric carbon dioxide. It said the Paris agreement could limit emissions to that level.

The climate conference, and debate over the text, including the ban on carryover credits, is due to end on Friday. It was not clear on Wednesday night Australia if agreement would be reached.

In a speech to the conference on Tuesday, Angus Taylor, the emissions reduction minister, said investments in technology were central to fighting climate change, but did not specifically mention the plan to use carryover credits.

Taylor said the Paris agreement “sent a powerful signal to the world that countries are serious about climate action”.