Business and political leaders are misleading the public by holding negotiations that are not leading to real action against warming temperatures, teen climate activist Greta Thunberg says.

"The real danger is when politicians and CEOs are making it look like real action is happening, when in fact almost nothing is being done, apart from clever accounting and creative PR," the Swedish 16-year-old said Wednesday in a speech at the plenary of the ongoing UN climate talks in Madrid, or COP25.

"Finding holistic solutions is what the COP should be all about, but instead it seems to have turned into some kind of opportunity for countries to negotiate loopholes and to avoid raising their ambition."

AP

The activist cited scientific reports that have established that unchecked warming above 1.5C for the planet would be catastrophic.

She also said pledges to reduce emissions were not enough, carbon needed to remain underground and greenhouse gases responsible for rising temperatures needed to be brought to zero.

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"This is not leading, this is misleading," she said, adding "every fraction of a degree matters".

Politicians in Madrid are grappling with outstanding issues in the implementation of the 2015 Paris Agreement, which aims to avert catastrophic global warming, including the spiny issue of accounting for carbon emissions.

Many countries and companies are relying on the idea of carbon markets to meet goals to cut greenhouse gas output and help limit temperature rises to between 1.5-2 degrees Celsius above pre-industrial levels.

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Supporters of carbon markets say they can serve to lower the cost of reducing emissions and enable countries to commit to more ambitious targets. Others see them as a way to stall more aggressive action to cut emissions.

Ms Thunberg said many pledges to balance out emissions in this way did not include the impact of shipping, aviation and international trade, and called for quicker action.