Global warming could be worse than expected this century, rising more than five degrees, if lawmakers don’t move to enact policies that will reduce greenhouse gas emissions, researchers at the Massachusetts Institute of Technology said today.

According to the new projections using computer simulations, the earth's surface has a median probability warming of 5.2 degrees Celsius by 2100, with a 90 percent probability range between 3.5 to 7.4 degrees.

This can be compared with a median projected increase of just 2.4 degrees in a 2003 study, MIT said Tuesday.

The new projections consider several factors such as improved economic modeling and newer economic data showing less chance of low emissions than had been projected in earlier scenarios.

Other factors in the new model include the cooling effect induced by 20th century volcanoes and the emissions of soot and measurements of deep ocean temperature.

Without action, there is significantly more risk than we previously estimated, said Ronald Prinn, the co-author of the study. This increases the urgency for significant policy action.

Prinn is a co-director of the Joint Program and director of MIT's Center for Global Change SciencePrinn.

The study is being unveiled as the U.S. Congress holds a series of hearings this week to pass climate legislation aimed at cutting greenhouse gas emissions 17 percent from 2005 levels by 2020. The legislation will also promote renewable energy sources, and the establishment of a cap-and-trade system for carbon emissions.