MISSOULA - James Hansen, NASA's top climate change scientist, will talk about human impacts on global warming Monday at the University of Montana.

In western Montana, climate change is having a major impact.

The snowpack melts earlier. The spring growing season starts earlier. Summer droughts are longer, which increases wildfire risks and lowers streamflows.

"We aren't having just a single impact, but three or four sequential impacts," said UM professor Steve Running, a member of the U.N. climate change panel that recently received the Nobel Prize.

Running will introduce Hansen, whose talks are part of the President's Lecture Series at the school. Hansen's two lectures are free and open to the public.

Running encouraged western Montanans to attend Hansen's evening lecture, which is geared for the general public.

"This guy's the oracle of climate science. He's like the Allen Greenspan of economics," Running said. "We won't get anyone of his caliber again in Missoula.

"If anybody wants to understand our best guess of our future climate, here's the guy to hear it from."

Hansen, director of NASA's Goddard Institute for Space Studies, will give a seminar titled "What Determines Climate Sensitivity?" at 3:10 p.m. in Gallagher Business Building, Room 123.

His 8 p.m. lecture titled "The Threat to the Planet: How Can We Avoid Dangerous Human-Made Climate Change?" will be at the University Center Ballroom.

Hansen will discuss social and economic solutions to global warming, including electricity generation, vehicle gas mileage standards, and wind and solar power.

"He's really going to go through the kinds of options that society has to engage in to work our way out of this," Running said.

Hansen has said human-caused climate change will become unstoppable by 2016 if levels of greenhouse gases such as methane and carbon dioxide are not significantly reduced.

A critic of the Clinton and current Bush administrations' stances on global warming, Hansen has directed NASA's Goddard Institute since 1981.