How did you first meet Thompson? What drew you to him and his work?

Madeleine: We first connected in 1997 when I called him on the phone. At the time, I was writing a story about the powerful El Niño that had arisen that year, and I was fascinated that his ice cores contained a record of El Niños and La Niñas that went back 1,500 years. The following year I met him in person. I still vividly remember the encounter between Thompson and paleoclimatologist Rick Fairbanks at the American Geophysical Union meeting in December 1998. They were trading tales about hardships they'd endured in the field. "Lonnie's war stories are better than mine," Fairbanks humorously noted.

And then, in the summer of 2000, Thomas (my husband) and I went with him on a small expedition to the Quelccaya ice cap in southern Peru. It was one of the most challenging things I've ever done. When I got to the top of the ice cap at 18,700 feet, I felt I had accomplished something big. When you go on expeditions with people, you grow to understand them in a deep, almost visceral way. It was then, I think, that I grew to appreciate what Thompson goes through to get his ice, how much physical and mental strain is involved.

Do you and your husband work together a lot?

Madeleine: Not all the time, but we've done some very nice stories together. In 2002 we went to Antarctica as a writer-photographer team for Time. We've also collaborated on travel pieces that appeared in the Chicago Tribune. What's nice is that, later on, when I'm writing, I can pull up his photographs and the whole experience of being in a different place comes flooding back. We keep on talking about doing a book together. Maybe we will!

Did either of you have any difficulty with the elevation?

Madeleine: Oh yes. Even though we were both taking Diamox [a drug prescribed for altitude sickness], and even though we were careful not to ascend too quickly, I still felt robbed of energy and, indeed, lost appetite to the point that I had trouble forcing myself to eat. I think I was losing about a pound a day. After Thompson and the others established themselves in the high drill camp, my husband and I debated whether or not we should follow. In the end, we decided against it. The high mountains are unforgiving places; before going farther, I needed to feel I had enough energy in reserve to be able to deal with any problem that might arise—and I clearly didn't. I thought Thompson's description of the climb as "a walk in the park" was highly amusing!

Thomas: The Antarctica story prepared me for dealing with cameras in extreme climate conditions, so I researched the issues that might come up in Tibet. Since I am now shooting digital, using a Nikon D2X, I need to be able to back up images to a computer disk. Few people realize that personal computer hard drives are only qualified to 10,000 feet, and we were over 16,000 feet for over a month. The pickup heads that fly over the spinning disk are held up like an airplane by the air inside, but, of course, they are only a tiny distance above the magnetic surface. As the air gets thinner, the lift reduces. The drives will work higher than 10,000 feet, but the probability of a crash goes up. I carried five portable disks and backed up every image onto at least three of them as soon as I could. The raw images take lots of space, so I was carrying over 400 gigabytes of disk! The MacBook worked fine at the truck camp at 16,000 feet. When I got up to the mid-camp at 17,800 feet, I turned on the MacBook and it did not boot up the first time. I tried again and I saw a message from the operating system I never want to see again—something about "can't find the data"—the data being all the pictures I had taken up to that point. After gasping and catching my breath (no easy matter at that site), I quickly shut the computer off and left it off until I got down to 16,000 feet two weeks later. There it worked well again; all the pictures were still there. In the meanwhile, I stored the images on 16 gigabytes of flash cards the camera uses. Since those cards do not use mechanical devices, they work well at altitude.

Were any of the photos tough to capture?

Thomas: The picture of Lonnie Thompson in front of the glacier was taken on a rocky outcrop at 18,700 feet on the route to the ice camp. Lonnie is a very good subject and cooperative, but I may have delayed his trek upward as he arrived at the ice at dusk.

The sunset picture of Naimonan'yi came as we were a bit lost, searching for the right track into the valley where our truck camp was set up. We were late and it was getting dark because it had been a rather eventful day—one of the four-wheel-drives had rolled over on the bottom of a 17,000-foot pass and that had caused a delay. No one was hurt, but we were quite worried for a while. Even though it was late, the Chinese driver understood my hollering "Stop! Stop!" when I saw this image opening up.

Lonnie in the negative 30 degree Fahrenheit freezer at Ohio State reminded me of photographing at the South Pole at just about the same temperature. We spent quite a bit of time getting pictures amid all that amazing ice, a record of the earth's climate history. I think we would last for about five minutes at a time before we had to go back outside to get my hands warmed up. Each time I went out I had to put the camera into a big baggie to keep moisture from condensing into frost all over it!

Madeleine, you mention that it can be frustrating getting enough yaks, waiting for trucks that never come, etc. As a science writer, do you find that the pursuit of scientific knowledge includes a lot of waiting around and dealing with inconveniences?

Madeleine: Thompson and I have a lot in common, I think. One trait we share is persistence to the extreme. For example, it took three years for the plans for the expedition to gel, and for my husband and me to get the required visas and permits. In 2004, for example, we were hoping to go with Thompson on an exploratory expedition to Naimona'nyi, but our paperwork did not go through, so he and the other members of his team went without us. I don't like giving up, and I almost never do—which is why I had real trouble admitting to myself that I should not try to go up to the drill camp.

What struck you about Tibet while you were working on this story?

Madeleine: I was stunned by the vastness of the Tibetan plateau, by its emptiness, by its harsh beauty.

Thomas: This was a wonderful adventure. I will always remember the shy, yet welcoming faces of the Tibetans and the prayer flags at every pass as we went deeper and deeper into the remote western regions on the five-day drive.

Madeleine, as someone who knows more about weather and climate than most people, do you think you worry about climate change more?

Madeleine: No doubt I do. And what worries me most is how limited our understanding of the climate system still is. But what we do know is highly disturbing: the climate system is non-linear, which is a way of saying that it is subject to sudden reorganizations once critical thresholds are crossed. Just where these critical thresholds lie we don't yet know. All we can hope is that the experiment we've launched, using our planet as the guinea pig, won't turn out too badly.

Are you hopeful that we will be able to slow down climate change, or do you think we've already done too much damage?

Madeleine: I think that slowing down climate change—the part of climate change that is due to human activities—is the only option we have. And I think that human societies are beginning to move in that direction. My question is whether they will be able to move fast enough. The speed at which ice is now disappearing from large sectors of the world suggests that there may not be a whole lot of time for dawdling. This is how I once expressed it: All anyone can say is that two extremely large and complex systems—the climate system and the human system—seem headed for confrontation, and more than anything else, it is the uncertainty of how each of these systems is likely to react to the other that makes the buildup of greenhouse gases so troubling.

And yet the climate system is fundamentally deterministic. In principle, the human system is more flexible; it has the capacity to respond to change, even the prospect of change in ways that are imaginative and innovative. The dramatic tension in the confrontation that looms in the twenty-first century emanates from that essential difference.