If you asked me the height of Mount Everest, I could tell you without missing a beat: 29,029 feet (I don’t know it by heart in meters, but it’s 8,848 m).  That’s been the accepted height since the 1954 Survey Of India, which established the height using a number of observation stations and triangulation (trigonometry). Since then, there have been a few other measurements, all yielding heights close to the 1954 data: a 1999 National Geographic measurement gave 29,035 feet (seven feet higher), while a 2005 Chinese survey yielded 29,017 (that was the rock height, neglecting the roughly ten feet of ice and snow covering the summit).

There’s no doubt that Everest’s summit is the highest spot on earth measured from sea level (Chimborazo in Ecuador, however, is the highest mountain measured from the Earth’s center), but people want an exact figure. This article in the new National Geographic (click on screenshot) shows the difficulty of actually getting that figure.

First of all, the height of Everest keeps changing, both rapidly and slowly. Slowly because it’s still rising as the Indian tectonic plate collides with the Asian one—the event that created the Himalayas to begin with. That rise is about 0.5 centimeters per year. The more rapid changes are due to earthquakes: one in 1934 is supposed to have lowered the mountain by two feet. Then there’s the decision about whether to count the ice and snow blanketing the peak in its total height, for that blanket can be up to ten feet thick. (Triangulation of course includes that.)

Finally, there’s the tough decision about the baseline, taken as “sea level.” The problem is that calculating “sea level” is hard because it varies from place to place and time to time due to irregularities in the Earth’s shape, and so what they’d like is “what the sea level would be under Mount Everest if there were sea under Mount Everest”.  That involves making two models, as depicted in the figure below from the article, and it’s apparently the sum of the geoid height and the ellipsoid height is the mountain’s height. (It’s a bit complicated, and I can’t say I understand it fully, because sometimes the geoid height looks to be negative.)

The first of two recent sets of measurements were taken by a Nepalese survey team that climbed Everest in 2019, summiting in the middle of the night to avoid the rush of climbers.  Laser trigonometry as well as GPS technology established the summit height. They also used a method to determine the thickness of ice and snow on the summit. That “official” height is now known but hasn’t been revealed, for the Chinese get a say as well: the border between China and Nepal runs right through the summit, and so this spring, when all expeditions were canceled because of the pandemic, the Chinese used a combination of climbers and a surveying plane to get their own height (see below).

And politics are involved as well:

Nepal, one of the poorest nations in Asia, has numerous reasons to keep its wealthy and powerful neighbor happy. During the last fiscal year, some 90 percent of foreign direct investment in the nation came from China, and during his state visit, Xi pledged $500 million in financial aid. This comes in addition to the millions of dollars China has invested in Nepali infrastructure projects, including new airports, railways, and hydropower plants.

There is precedent for Nepal and China coordinating on the issue of Everest’s height. After the Chinese completed their 2005 survey, Nepal and China announced a joint agreement to recognize both the new Chinese survey of the highest point of rock and the 1954 Survey of India elevation, which included the snowcap.

So we’ll have at least two new heights, and they’re very unlikely to be identical. But it doesn’t really matter, as Everest will remain the highest spot on Earth—calculated from an estimated sea level. That’s why I trekked in to see it twice, and why so many have tried, and many have died, trying to stand on the roof of the Earth. It’s a beautiful place to visit, and an excellent trek, and I’m content to not have climbed it. Seeing it was enough, for, believe me, you may think you’ve seen high mountains, but, like Crocodile Dundee’s knife, this is a mountain! I wish I could embed some of the photos I took on my trips, which are on 35 mm Kodachrome slides.

Here are two photos from recent measurement efforts. Photos and captions are from National Geographic:

From the recent Chinese expedition:

Below is an informative but scary chart from the Encyclopedia Brittanica, showing the peril of trying to climb it. Even I got cerebral edema climbing the small peak next to it, Kala Patthar, which is only 18,519 feet (5,644 m). That, and not base camp, is where you get the view of Everest in all its glory. (You can’t see anything from base camp.)

I made it up and down Kala Patthar on both treks, but the second time I got cerebral edema, wanted to lie down and sleep (my companion stopped me from that, knowing I’d die) and I repeatedly stumbled trying descend. I stopped at the Trekker’s Aid Post nearby for a checkup, and they told me what I had and that it would go away when I descended. (A doctor inhabits a quonset hut during the trekking season.)  I hiked down to 15,000 feet, and then I was fine.

Here, from Wikipedia, is the view of Everest from Kala Patthar. On both days I climbed the small mountain, it was perfectly clear like this, and the view was stupendous. (There was also plume of snow from Everest’s summit, showing high winds.)

h/t: Andrew Berry, a fellow Everestphile