"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."
The activist,whose speech garnered wide applause,cited scientific reports that have established that unchecked warming above 1.5 degrees Celsius 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.
"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.