March 7, 2004

‘Snow Fooling!

Mt. Kilimanjaro’s glacier retreat is not related to global warming. The media and scientists blamed human activity, but a 120-year-old natural climate shift is the cause.

Despite countless reports blaming global warming, it turns out Mt. Kilimanjaro’s glaciers are retreating because of a climate shift that occurred more than 120 years ago, long before humans could have caused it.

Reports of the glacier retreat heated up around 2/19/01, when the New York Times reported on the findings of glaciologist Lonnie Thompson in an article it headlined “The Snows Are Leaving Kilimanjaro; Fabled African Peak Offers Clear Sign of Global Warming.” Thompson had presented a paper the day before at the American Association for the Advancement of Science (AAAS) annual conference.

The Times article prompted a media feeding frenzy. Even today, a Google search on “Kilimanjaro global warming” produces 4,200 hits, with sources including the BBC, National Geographic and other trusted media outlets.

AAAS publishes Science, which one year later carried the peer-reviewed version of Thompson’s conference presentation. During this process, we wrote two articlea (; demonstrating that these stories are largely composed of, well, hot air. Something other than warming, likely a change in precipitation that is opposite what you might expect from warming, was shrinking the world’s most iconic ice cap.

We didn’t expect the New York Times to sit up and take notice, although our articles certainly contributed to a healthy skepticism about glib reports on human activity melting Hemingway’s inspiration.

Still, you’d think there would be just a little coverage when, two years later, a major scientific journal echoed what we discovered with just a few hours of research. According to Georg Kaser and four co-authors, writing in the 3/15/04 International Journal of Climatology, “A drastic drop in atmospheric moisture at the end of the 19th century and ensuing drier climatic conditions are likely forcing glacial retreat on Kilimanjaro.”

Here’s the embarrassing fact. The late 19th century was long before human activity had resulted in major emissions of greenhouse gases such as carbon dioxide, methane, and chlorofluorocarbons (the latter wouldn’t even be invented for another half-century). Therefore human-induced global warming has nothing to do with the decline of Kilimanjaro’s ice cap. That fact is going to be very hard to write for people who adamantly reported the opposite.

But they should have known better to begin with. Indeed, any reporter with a modicum of critical insight or skepticism should have picked up that there was a problem with the notion of human activity leading to glacier retreat on Kilimanjaro.

Consider that, for example, between 1953 and 1976—a period of global cooling—a full 21% of the glacier’s original area disappeared, as Thompson reported in 2002. Where were the dire forecasts of disastrous results from global cooling? At the time, it would have been completely logical (if ultimately false) to predict the following: “If this cooling trend continues, Kilimanjaro’s glaciers will completely disappear by 2015.”

That cooling trend ended around 1976, replaced by a rise in the global surface temperature between 1977 and now. And guess what? The rate of glacial recession declined.

The slowed recession may have to do with the fact that, according to data collected by orbiting satellites, Kilimanjaro and the surrounding countryside also cooled during that era, despite an overall planetary warming (Figure 1). While there has been some quibbling about what the satellite is actually measuring in other places, scientists all acknowledge that it is most reliable at altitudes such as Kilimanjaro’s.

Kilimanjaro Satellite Temperatures

Figure 1. Satellite-sensed temperatures in Kilimanjaro’s neighborhood show a statistically significant decline since records began in 1979, which may be one reason why the rate of Kilimanjaro’s recession also slowed. None of the related news stories mentioned either the slowdown or the cooling.

Those facts were obvious in Thompson’s original 2002 paper, and should have tempered any subsequent press attempts to conflate warming and the decline in African glaciers. But they didn’t. And we doubt you’re going to be reading about Kaser’s findings in tomorrow’s papers, either. So you’ll have to read about them here:

Over the past 150 years, Kaser et al. report, “…the climatic evolution of East Africa…is characterized by a drastic dislocation around 1880, when lake levels dropped notably and glaciers started to recede from their latest maximum extent,” concurrent with the end of the Little Ice Age. The climate got dry, and stayed that way throughout the 20th century.

“Did this sudden drop in atmospheric moisture also initiate the recession of the glaciers on Kilimanjaro and force it until the present day?” Kaser asks. “This question is vitally important…since the recession of Kilimanjaro’s glaciers is widely attributed to global warming only (…Thompson et al., 2002).”

(The Kaser team says Thompson’s view is “overly simplistic,” noting that, “In the East African highlands, there is no trend in air temperature records that nearly span the whole 20th century.” No trend at all in the East African highlands? You would think that the reviewers over at Science magazine would have picked that one up before publishing Thompson’s paper!).

Kaser et al. continue: “Positive air temperatures have not contributed to the recession process so far. The rather independent slope glaciers have retreated above their elevation of thermal readiness, responding to dry conditions.”

Finally, what of the sure-shot reports that the glaciers of Kilimanjaro will be all gone by 2015? Nope. The glaciers on the slope of the mountain are likely to stay.

“If the present precipitation regime persists,” Kaser concludes, “then these glaciers will most probably survive in positions and extents that are not much different than today. This is supported by the [fact] that slope glaciers retreated more from 1912 to 1953 than since then.”

Environmental reporters of the world: Eat crow. The evidence was there two years ago in pages like these. And it has now made it all the way back into the refereed scientific journals. Where have you been?

(Note: We have brought the Kaser paper to the attention of Andy Revkin, the global warming writer at the New York Times. He will surely call it to the news editor’s attention. If you don’t see a story on it soon, you’ll be able to surmise what happened.)


Kaser, G., et al., 2004. Modern glacial retreat on Kilimanjaro as evidence of climate change: observations and facts. International Journal of Climatology, 24, 329-339.

Thompson, L.G., et al., 2002. Kilimanjaro ice core records: evidence of Holocene climate change in tropical Africa. Science, 298, 589-593.

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