Message in a bottle Steven Schultz     Geoscientist Michael Bender Some people are criticized for pulling numbers out of thin air. Michael Bender has made a career out of it -- and has helped scientists better understand our climate in the process. Every few days, a pair of clear glass capsules about the size of footballs arrives, packed in a cardboard box, at the labs of Princeton geoscientist Michael Bender. The capsules contain air -- plain air collected aboard a merchant ship as it steams across the Pacific Ocean. What Bender does with the air is anything but plain, teasing out exquisitely precise measurements that create a broad picture of how the Earth's climate works and how human activity is changing it. Bender's air measurements are just one part of an ambitious research program. Doing similar work with ice, packed snow and ocean water, he has played a central role in mapping changes in the Earth's climate since the last ice age 100,000 years ago -- a record that contains a surprising array of sharp temperature shifts. In each case, Bender's trademark contribution has been to show how these seemingly mundane substances contain hidden records of the Earth's climate and to coax them into telling their story. "It's beautiful work," says Steven C. Wofsy, an atmospheric scientist at Harvard University. "Many people go out and make very good measurements. There are very few scientists who can think it all through and complete the story. That's Bender." The story Bender is telling could hardly be more important. As humans pump vast amounts of carbon dioxide into the atmosphere, scientists are faced with predicting the consequences. To do so, they need to understand the forces and events that shaped the Earth's history to this point. What caused the cooling and warming of the ice ages? How has the climate reacted to different levels of carbon dioxide in the past? Scientists test their grasp of such questions by developing computer models, or simulations, of the climate. They feed in the conditions at a point in the past, say the last ice age, and see how well the computer "predicts" how the climate evolved from there. Those tests give scientists more confidence about using today's conditions to predict future climate changes. "We can't build and test those models without the work Michael is doing -- that's the bottom line," says Richard B. Alley, professor of geosciences at Pennsylvania State University. With his air measurements, Bender helps solve a nagging problem about what happens to all the carbon dioxide we pump into the atmosphere. Scientists have known for years that only half this pollution stays in the air. The rest was a mystery: Is it accumulating in the oceans or forests, or both?     Michael Bender loads a sample onto a machine that draws off some air and compares its makeup to that of "laboratory" air of known content.   Bender and Ralph Keeling of the University of California-San Diego realized the answer rested in measurements of oxygen, not carbon dioxide. Burning fossil fuels adds carbon dioxide and depletes oxygen from the air, but trees using carbon dioxide for photosynthesis would restore some of that oxygen loss. After thousands of measurements, Bender and Keeling showed that the level of oxygen is indeed going down, but not as fast as it would without help from forests. Their conclusion is that forests are taking up an increasing amount of carbon dioxide pollution, possibly due to the reforestation of farmland. In these measurements, a tiny percentage change in oxygen concentration is crucial. "It's like looking at a stack of dollar bills and deciding whether there are 250,000 or 250,001. That one dollar is the difference between trees taking up none of human-produced carbon or taking up 20 percent of it," says Bender. Bender extended that work back in time by examining an archive of air pockets in the packed snow of Antarctica. Those samples showed that forests were not taking up a substantial amount of excess carbon dioxide 25 years ago, suggesting that reforestation of farmland has had a substantial effect on global climate. Digging even further into history, Bender studies columns of ice drilled from nearly four kilometers beneath the surface of Antarctica. These samples date to 400,000 years ago and reveal information not only about global temperature and carbon dioxide content, but how those measures differed between Antarctica and Greenland. "Michael has been a pioneer in putting different climate records on the same time scale," says Alley, "and he is one of the very few who looks at all the time scales." In each of his projects, Bender is driven not just by the desire to understand our climate, but by the intellectual challenge of finding new ways of capturing the information. In one project, he is developing a direct and reliable method to measure the total amount of photosynthesis occurring within an entire ocean. The test itself is relatively simple, but devising it required Bender's understanding of the complex way in which oxygen cycles between the oceans and the upper atmosphere. The reasoning goes like this: Sunlight in the upper atmosphere creates an unusual abundance of a certain oxygen isotope, and some of this skewed oxygen dissolves in seawater. Plant life in the oceans tends to erase this effect, so the more plant life, the less skewing of isotopes Bender observes in his seawater samples. A single sample of seawater contains information about plant life across a wide region of ocean. "It's a typical Bender operation," says Wofsy. "You hear him tell you about this test and the first thing you say is, 'That is never going to work.' Then he does it and you say, 'Oh yes, this is a great idea.'" Indeed the method could be a boon to marine biologists, oceanographers, climatologists -- anyone who needs a global gauge of ocean life. But for Bender, the excitement came in puzzling out a way to answer his question about the ocean by looking to the atmosphere. "That's just been tremendously satisfying," he says. "These questions are tremendously engaging intellectually," he adds. "They are also very significant for major policy decisions that need to be made." Bender's ability to draw on ocean biology, atmospheric science, oceanography and chemistry puts him at the cutting edge of the field of geosciences, which is increasingly trying to develop an integrated picture of what makes this planet habitable, says geosciences chair George Philander. "His work is at the center of gravity of this effort." Related article Air mail not so easy		[an error occurred while processing this directive]