From the we told you so, twice, no make that three times, department, the poster child for climate change is cited in the New Scientist where they say a peer reviewed paper shows that it’s mostly about the trees and evapotranspiration of moisture into upslope winds.
As mentioned in The New Scientist on September 25th, a recently published study in the journal Global and Planetary Change, reveals that due to deforestation, heating that occurs on the in the day leads to a flow of moist, warm air that flows up the side of the mountain, but that air is not as moist as it once was. The New Scientist has finally caught up to what we’ve known for some time.
Trees in the plains surrounding Kilimanjaro are very important, as they give moisture to the air through evapotranspiration. This study they cite suggests that the excessive and aggressive felling of trees in the last few decades has led to a decrease in the moisture flow up the mountain slopes, where it is deposited as precipitation by orographic lifting.
Kilimanjaro 1993, left and in 2000, right Image: NASA/USGS – click
Since the peak does not get replenished by the water and moisture that the air flow would normally bring from that evapotranspiration from trees, the snowpack starts decreasing. The snowpack compresses into glacier ice, and it evaporates through sublimation. Without additional replenishment, the ice gradually sublimates away, even if the temperature remains below freezing. Anyone who has ever watched ice cubes disappear in a freezer knows about sublimation at below freezing temperatures.
The icepack around Kilimanjaro’s summit is now measured to be approximately 15% of levels measured in 1912. Of course many use Kilimanjaro as a prime example of the effects of climate change. In An Inconvenient Truth, Al Gore stated that Kilimanjaro’s glaciers were disappearing because of “global warming”.
In fact, Gore’s Kilimanjaro claim failed a test in British court, along with many other claims made in AIT:
Mr Gore’s assertion that the disappearance of snow on Mount Kilimanjaro in East Africa was expressly attributable to global warming – the court heard the scientific consensus was that it cannot be established the snow recession is mainly attributable to human-induced climate change.
In the recent study, Nicholas Pepin from the University of Portsmouth in the UK suggests that deforestation is the reason for the decline of the snows of Kilimanjaro.
His group has studied the mountain extensively. Between September 2004 and July 2008, the Pepin team took hourly humidity and temperature readings at 10 elevations on the mountain to determine what has actually been happening.
Here’s the paper: Global and Planetary Change, DOI: 10.1016/j.gloplacha.2010.08.001
And the abstract:
The montane circulation on Kilimanjaro, Tanzania and its relevance for the summit ice fields: Comparison of surface mountain climate with equivalent reanalysis parameters
We compare surface climate (temperature and moisture) measured on an hourly basis at ten elevations on Kilimanjaro with equivalent observations in the free atmosphere from NCEP/NCAR reanalysis data, for September 2004–July 2008. On the lower forested slopes the mountain surface is consistently cooler and moister than the atmospheric boundary layer. In contrast, temperatures and moisture on the higher slopes above treeline (~ 3000 m) are decoupled from the free atmosphere, showing substantial heating/cooling by day/night and import of moisture up from lower elevations during daylight hours. The mountain is universally warmer than the background atmosphere at 1500 EAT, the sparsely vegetated upper slopes acting as the focus for the most intense heating. The persistent vapour pressure excesses (>5 mb) in the forest zone move upslope during daylight and subside downslope at night. Strong seasonal contrasts are shown in the vigour of this process, the resultant mountain thermal circulation and its consequences. The synoptic forcing of this process (as represented by flow indices developed from reanalysis wind components), although evident, is relatively weak. This means that upslope flow from the forest zone is an important supplementary source of moisture for the upper slopes of the mountain and that free-air variability, although important, alone cannot account for all the variability in the summit moisture regime. Long-term ice retreat at the summit of Kilimanjaro therefore is most likely to be influenced by changes in local land-use as well as more regional free-air changes.
Keywords: mountain climate; montane circulation; land-use change; ice-field
- 3.1. Background flow climate in northern Tanzania
- 3.2. Surface climate on Kilimanjaro and its comparison with background conditions
- 3.2.1. Temperature differences (ΔT)
- 3.2.2. Moisture differences (ΔVP)
- An observationally-derived model of the mountain circulation
- 4.1. Conceptual model
- 4.2. Comparison of field observations with model results