2009 Walter Orr Roberts Distinguished Lecture

Jim Hansen on Earth's climate: "We're now completely in charge"

NASA scientist James Hansen made a plea for concern and action on climate change—and offered his latest prediction on global temperature—in a UCAR-sponsored talk on April 9. Hansen delivered this year’s Walter Orr Roberts Distinguished Lecture before a full house of about 2,000 at CU’s Macky Auditorium. The talk was part of the university’s annual Conference on World Affairs.

Jim Hansen

Hansen stressed how three different lines of evidence—paleoclimate studies, observations, and modeling—all point to the increasing role of humans in the global climate system. He noted that global temperatures peaked around 65 million years ago, before ice ages began and polar ice sheets formed. Carbon dioxide concentrations are currently less than half of what they were during that global temperature peak, Hansen said, but the Sun is more intense. That will provide additional climate forcing at the same time that humans are injecting greenhouse gases into the atmosphere at an alarming rate.

“We’re ten thousand times more powerful than the natural geological changes to atmospheric composition,” he said. “We’re now completely in charge.”

When discussing the importance of reducing greenhouse-gas emissions, Hansen invoked his own grandchildren and spoke of a “basic conflict” between powerful fossil-fuel interests and the comparatively powerless. He remains hopeful that changes in fuels and land use can eventually bring carbon dioxide concentrations back down to 350 parts per million, which he believes could help avert the loss of ice sheets and other dire consequences. “It’s technically feasible,” Hansen said, repeating his recent call for a moratorium on building coal-burning power plants unless and until the carbon emissions from such plants can be sequestered.

Hansen favors a carbon tax rather than a cap-and-trade system to reduce national and global emissions, since he believes the latter could be “loaded with escape valves” and more prone to financial shenanigans: “We’d end up making Wall Street millionaires at public expense.”

Over the years, Hansen has made several informal predictions on global temperature; he correctly pegged the brief cooldown after 1991’s eruption of Mount Pinatubo and the return to record global highs thereafter. In his Macky talk, noting that that global averages haven’t risen the last several years, Hansen pointed to La Niña, which has brought relatively cool water to the surface across much of the tropical Pacific since 2007. Assuming that the next El Niño arrives soon, he said, “We’ll be back to record global temperatures again within a year or two.”

The UCAR lecture series, established in 1998, pays tribute to Walter Orr Roberts, the founding head of UCAR and NCAR, and honors the presenter's accomplishments. Previous WOR honorees have included NCAR’s Warren Washington and John Firor and NOAA’s Susan Solomon.


Jim Hansen receives

UCAR president Rick Anthes introduced Jim Hansen and presented him with a plaque commemorating the lecture. (Photos by Bob Henson.)