The author of an influential 2006 study on climate change warned Tuesday that the world could be headed toward warming even more catastrophic than expected but he voiced hope for political action.

Nicholas Stern, the British former chief economist for the World Bank, said that both emissions of greenhouse gas and the effects of climate change were taking place faster than he forecast seven years ago.

Without changes to emission trends, the planet has roughly a 50 percent chance that temperatures will soar to five degrees Celsius (nine degrees Fahrenheit) above pre-industrial averages in a century, he said.

“We haven’t been above five degrees Centigrade on this planet for about 30 million years. So you can see that this is radical change way outside human experience,” Stern said in an address at the International Monetary Fund.