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GUY RAZ, host:

Kent Moore also studies climate change. He is an atmospheric physicist at the University of Toronto, and he's also an amateur mountain climber, and like many mountain climbers, he was always interested in the story of the doomed expedition to Mount Everest in 1924, a journey that left George Mallory and his partner, Andrew Irvine, dead as they attempted to reach the summit.

No one really knows what happened as they got closer. The last man to see them alive was Noel Odell. He was at the base camp on June 8, 1924 and watched the two men climb. Here's how he remembered the day they vanished. This is from a "Nova" documentary produced in the mid-1980s.

(Soundbite of television program, "Nova")

Mr. NOEL ODELL: It was blowing very hard and blowing snow and mists and stuff. Visibility was bad, very bad.

RAZ: Odell also kept copious records, barometric pressure readings and other weather data, and this is where Kent Moore comes in. He wanted to get a hold of those records to see if he could track climate change in Tibet, but what he found was something completely different.

Mr. KENT MOORE (Atmospheric Physicist, University of Toronto): So I was on my way to a meeting in Norway, and I had a layover in London and a few hours to kill. So I decided to go to the library of the Royal Geographical Society, which has all the Everest records there. They were very gracious in bringing out this old kind of, you know, torn folder full of grainy pieces of paper. I had to put on gloves and use tongs to kind of move these papers around because they were obviously of historical interest.

And to my amazement, I actually found the weather diary from the expedition that included these pressure measurements that had been made at base camp. I remember I started looking and reading the numbers and going, oh, gee, there's this huge pressure drop. I go, gee, I hope this is the day they were summiting on because I couldn't remember if it was the 8th or the 9th.

And so I quickly checked my records, and in fact, it was the day that they in fact were summiting. So that pretty much told me that we had sort of uncovered a pretty important piece of information as to what happened to them.

RAZ: Explain what the going assumption has been about what happened to the men as they approached Everest's summit.

Mr. MOORE: No one really knows what happened to them. They know that Mallory fell. His body was found below the ridgeline. There was some evidence that he was not roped at the time. So that means that he was unroped from Irvine, and that's a thing that wouldn't have happened unless something had happened to Irvine earlier.

So there are still lots of uncertainty as to what in fact happened to them. They were climbing for about two days before they reached the high camp from which they made their summit attempt, and during that whole period of time, the barometric pressure or the atmosphere pressure at base camp was dropping.

And anyone who's a sailor knows that when the pressure's dropping, that usually means that there's an indication that a storm is coming towards you. And so what this data showed us was in fact that Mallory and Irvine were climbing into a condition where the pressure was dropping, and in fact, most likely there was a storm that developed on the day they were summiting.

RAZ: Would it have affected oxygen levels up there?

Mr. MOORE: When you get close to the summit of Mount Everest, there's just enough oxygen available for you to maintain your, essentially, your core temperature. So there's almost no oxygen available to do any work, that is to climb.

And so one of the things that happened while Mallory and Irvine were climbing is, as this pressure was dropping, in fact there was even less oxygen available than there usually is. And we think that that drop in oxygen was sufficient to cause hypoxic stress to their bodies, and that probably contributed to their deaths.

RAZ: And what happens to a human in that state?

Mr. MOORE: When we go high in the atmosphere, what happens is that the blood thickens, and some of the fluid that was originally in your blood is essentially excreted into your lungs or into your brain.

When the fluid swells into your brain, you generally lose your cognitive ability. So you tend to become more disoriented. It takes you longer to do things. You forget things.

I've been as high as 6,000 meters. It's not a very natural state for human beings to be in. That took me about 20 minutes to put my shoes on in the morning just because you're kind of in a thick kind of funk.

But more seriously, when you get higher up on the mountain, this lack of cognitive ability leads people to do very strange things like stop moving, sit down, and there have been many recorded instances of very experienced climbers becoming disoriented at high altitude and refusing to come down, and in fact, on occasion they have been left there and eventually have died, most likely from hypothermia.

RAZ: Now, a big part of the legend behind the story of Mallory and Irvine is whether they actually made it to the top of Everest in 1924 and then died while coming down. Obviously, the credit is given to Edmund Hillary and Tenzing Norgay. They did it 30 years later. They are regarded as the first men to reach the peak. Does your research in any way clear up the mystery?

Mr. MOORE: What our research shows is that in addition to all the other stresses that they were under the uncharted route, the technical difficulty on the mountain they're also climbing in quite a bad storm, one that we think is quite similar to the 1996 "Into Thin Air" storm that Jon Krakauer wrote about, in which eight people died.

And that would have made it very, very difficult for them to continue on. And either they fell and died on the ascent up, or the bad weather was such that it forced them to turn around and come back down, and then they died on the way down.

So we'll never really know, but I think it's clear from our research that the weather did play a significant role in their disappearance.

RAZ: That's Kent Moore. He's an atmospheric physicist at the University of Toronto. His findings on the Mallory and Irvine expedition are published in the latest issue of the journal Weather. Kent Moore, thank you so much.

Mr. MOORE: It's been my pleasure.

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