Christiana Figueres told a meeting of the CEOs of coal companies on the sidelines of a UN climate conference that their industry needs to change radically to curb emissions of greenhouse gases and leave most of the world's remaining coal reserves in the ground.
"Let me be clear from the outset that my joining you today is neither a tacit approval of coal use, nor is it a call for the immediate disappearance of coal. But I am here to say that coal must change rapidly and dramatically for everyone's sake," she said at the International Coal and Climate Summit, organised here by the Polish government and the World Coal Association.
The World Coal Summit is taking place shortly after findings of the UN Intergovernmental Panel on Climate Change (IPCC) were published establishing that climate change is real and accelerating.
Figueres' decision to address the coal conference had invited strong criticism from green activists attending the COP 19, the UN summit on climate change.
Environmental organisations like Greenpeace has said that the Executive Secretary of the United Nations Framework Convention on Climate Change (UNFCCC) should choose clean energy over "dirty fossil fuels".
The ongoing UNFCCC talks will seek to strike a new, global deal by 2015 on curbing climate-altering greenhouse gas emissions.
According to the International Energy Agency (IEA) coal accounted for 44 per cent of carbon dioxide (CO2) emissions in 2011, the largest share, and remains the main source of electricity.