April 14, 2009 | 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.

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.

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

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