The IPCC's 2007 report had warned of rising sea levels, expanding deserts, more intense storms and the extinction of up to 30 per cent of plant and animal species.
Field, however, said that report had failed to take into account new coal-fired power stations in developing countries like China and India, and the huge increase in carbon emissions they would create.
"Without aggressive attention, societies will continue to focus on the energy sources that are cheapest, and that means coal"
Intergovernmental Panel on Climate Change
"Without aggressive attention, societies will continue to focus on the energy sources that are cheapest, and that means coal," he said.
Predictions of a decrease in carbon emissions had also been too optimistic, he said, as no part of the world has seen such a decline between 2000 and 2008.
Bolstering Field's arguments, Anny Cazenave of France's National Centre for Space Studies, told the meeting that new satellite measurements show that sea levels are rising at an increased rate, due to warming waters and melting ice sheets.
Field further said that there was a "real risk that human-caused climate change will accelerate the release of carbon dioxide from forest and tundra ecosystems, which have been storing a lot of carbon for thousands of years."
That could raise temperatures even more and create "a vicious cycle that could spiral out of control by the end of the century," he said.
Several recent climate models have estimated that the loss of tropical rainforests to wildfires, deforestation and other causes could increase the concentration of carbon dioxide in the atmosphere from 10 to 100 parts per million by the end of the 21st century.