Kilimanjaro not melting after all
A fresh assessment suggests the famous ice fields on Africa's tallest mountain will be around for decades yet. Recent concerns that climate warming would rob Mount Kilimanjaro of all its glaciers within 20 years are overly pessimistic, say Austrian scientists. Their weather station data and modelling work indicate the tropical ice should last well beyond 2040.
Precipitation and not temperature is the key to the white peak's future, the University of Innsbruck-led team says. "About five years ago Kilimanjaro was being used as an icon for global warming. We know now that this was far too simplistic a view," said Thomas Moelg. "We have done different kinds of modelling and we expect the plateau glaciers to be gone roughly within 30 or 40 years from now, but we have a certain expectation that the slope glaciers may last longer," added colleague Georg Kaser.
The group's assessment was presented here at the European Geosciences Union General Assembly meeting. It acts as a counterpoint to the most doom-laden projections for the 5,895m-high (19,340ft) peak, which draws thousands of tourists intrigued by the idea of seeing ice just three degrees south of the equator.
The research team has been using three automated instrument stations on the top of the mountain to collect continuous data on temperature, pressure, solar radiation, humidity and wind. The recording effort was in position late last year to witness heavy snowfall, which will have led to a slight increase in Kilimanjaro's overall ice volume. This glacier growth is only temporary, however. The mountain's ice is dependent on the pulses of moist air that sweep across from the Indian Ocean.
Since the late 1800s, these have become less frequent, and the regular snows that would maintain the ice fields are now a rare occurrence in what has become a much drier climate in East Africa. Today, the total ice extent - on the slopes and on the plateau - is about 2.5 sq km, down from more than eight sq km in the early 1900s. Some scientists have drawn a fairly straight-line curve and forecast a rapid final retreat to a totally bare mountain. But the Innsbruck team is more optimistic about the medium term having now put real field measurements into a comprehensive modelling programme. "Glacier recession has been a feature on Kilimanjaro for more than 100 years, but this is the first time we really have a precise understanding of the physical processes that control the glacier-climate interaction on Africa's highest mountain," said Dr Moelg.
This work emphasises the significance of the lack of precipitation (250mm per year on the summit) versus temperature (a mean of -7C). It indicates that glacier mass loss would be about four times higher if precipitation decreased by 20% than if air temperature on the mountain rose by 1C. Furthermore, it suggests that two-thirds of the ice that is lost goes straight into the atmosphere through sublimation (the direct conversion of snow and ice to water vapour). "In recent years many people have talked about 'the melting glaciers of Kilimanjaro'. If one wants to be more precise, I would call it the 'evaporating glaciers of Kilimanjaro'," said Dr Moelg.
This confirms the view that the African peak does not play an important role as a reservoir for water, unlike in the Andes and the Himalayas where some lowland cities and agricultural systems are dependent on summer melt high in the mountains. "This is not a factor at all at Kilimanjaro and it never has been," said Professor Kaser. "If you brought all the remaining ice down to the Amboseli National Park and melted it, the water would only cover the park to a depth of one or one-and-a-half millimetres. There is nothing in terms of water up there."
The Innsbruck research was conducted in collaboration with the University of Otago, New Zealand, and the University of Massachusetts, US. The team stresses that the drying of the East African climate around Kilimanjaro may itself be a regional impact of global climate change.
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