Sea sick?: Disruption of the ocean conveyor, below, could signal rapid climate change, says Lozier, bottom, who monitors how increased carbon affects ocean health; Arctic polar bear seeks stable ground amid melting ice

Aurora/Ty Milford

My decision  to search for some perspective on climate predictions takes me only one floor up from Lozier's office in Old Chem; my footsteps clap off the aging concrete stairs, polished by seventy-five years of students in motion. To get to Thomas Crowley, I walk through two small lab rooms, past a finger painting tacked to the bulletin board, past teetering stacks of journals on the floor beneath an open file cabinet, and into an office covered from floor to ceiling in shelved journals. Piles of article reprints, two rows deep, conceal most of his two desks. (Later, in an e-mail message to a photographer who is attempting to lure him outdoors for a photo shoot, Crowley says, "I would much rather have a picture taken in my office—surrounded by the stacks of paper that are the fodder for my research.")

Crowley's professional identity is hard to nail down. A geologist by training, he has become a historian and modeler of past climates and is now dealing with contemporary climate issues and policy. He works with computer models that apply Newton's equations of motion and the laws of thermodynamics to a rotating sphere and are run on the biggest computers in the world.

Disruption of the ocean conveyor could signal rapid climate change

University Corporation for Atmospheric Research

At this, the warmest point in human history, Crowley recognizes that we need a wholesale change in our energy supply—85 percent of which is carbon-based—to stabilize the climate. (Like other experts, Crowley points out that despite valid concerns over the contribution of automobiles to global warming, "most CO₂ comes from smokestacks not tail pipes"—which explains why none of my interviews involves more than a passing discussion of automobile fuel efficiency and emissions.) Even so, he is open to the idea of continuing the use of fossil fuels and to expanding the infrastructure, like offshore drilling, that provides them—as long as there are "tithes paid and horse trades made," he says. These tithes and trades might include money given to support production of alternative fuels or educational programs and scholarships funded by energy companies in states where fossil-fuel infrastructure is built.

"It takes time to rewire the energy economy, and clean coal or methane creates jobs and U.S. energy security," Crowley explains. But he draws the line at on-site drilling in the Arctic National Wildlife Area Refuge because the infrastructural footprint is just too big.

Crowley, who never eats lunch in his office because he prefers to eat with the students, invites me to join him. "Gabi doesn't like to sit up here," he tells me of his wife as he climbs to a table on the platform at the end of the gallery in the Union Building. Gabi is Gabriele Hegerl, the member of the Climate Research Committee I encountered at the National Academy. In line at the coffee counter after lunch, Crowley sifts through a handful of foreign coins, relics of Hegerl's service on advisory bodies like the Intergovernmental Panel on Climate Change (IPCC)—considered the authoritative source for climate-change predictions—which takes her all over the globe.

The oceans are assimilating up to 40 percent of the carbon byproducts of our daily lives, says oceanographer Susan Lozier.

Photo courtesy of Susan Lozier

I wasn't able to interview Hegerl that day because she was in Hawaii as part of a panel about changes in climate extremes. Later, by phone, she tells me that she recognizes the irony of flying all over the globe to climate-change meetings in emissions-spewing, fossil-fuel-swilling jets. Hegerl was a lead author of the IPCC 4th Assessment Report (2007), a comprehensive picture of the current state of knowledge about climate change—a four-volume report that was six years in the making and included the work of scientists from more than 130 countries. The report's take-home message is that the observed changes in climate over the past fifty years are "very likely" due to greenhouse gas emissions from human activities. "Very likely" is what Hegerl calls a statistical qualifier, because the scientific determination, as strong as it is, can't be considered 100 percent certain. (Remember, even evolution is referred to as theory, despite the fact that biologists see it as the foundation of the work they do.)

Hegerl says that her role as a scientist is to provide information to the public; it is up to the public to decide which consequences are acceptable. A self-described optimist by nature, she thinks that the public's will to act—regulation, legislation, changes in individual behavior—seems to be increasing.

Crowley, on the other hand, tells me, "I am never optimistic but veer between being hopeful and pessimistic." Walking back to Old Chem, coffee in hand, he explains that predictions about climate change have changed very little in the past twenty-five years. "We can predict a range of warming scenarios, depending on different population and emission scenarios, which is the sociological component of climate science," he says. "If we take the median value in that range of predictions, our climate will be warmer at the end of this century than it has been in between five and twenty million years."

There is no way, Crowley says, to explain twenty-first-century climate, with its Arctic sea ice retreat, summertime rivers on the Greenland Ice Sheet, and polar bears drowning for want of floating way stations, without factoring in the greenhouse gases that we've released into the atmosphere.