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Development Roast https://inesad.edu.bo/developmentroast/2009/03/reconciling-melting-glaciers-and-falling-temperatures-in-the-bolivian-highlands/ |
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Reconciling melting glaciers and falling temperatures in the Bolivian highlands Bolivia's rapidly diminishing Chacaltaya glacier has been widely used as a symbol of Anthropogenic Global Warming (1) 1. However, it is an unfortunate choice of symbol, because the retreat of this specific glacier is demonstrably not due to increasing temperatures caused by CO2 emissions.
All long-run monthly temperature series for the Bolivian highlands, including the La Paz/El Alto station, which is located near Chacaltaya, show cooling trends over the last six decades of about -0.2ºC/decade (2) 2. This is confirmed by more recent daily temperature anomalies from the University of Dayton Daily Temperature Archive since 1995 (see Figure 2). There is a statistically significant negative trend of -0.11ºC/decade since 1/1/1995 (98% confidence). The average anomaly for the 1995-2009 period is -0.6ºC, suggesting that the recent negative trend is a continuation of a longer trend, as suggested by the monthly data.
1. How can the falling temperatures in the Bolivian highlands be reconciled with the visibly diminishing glaciers? 2. Why are temperatures falling, when they are supposed to be increasing? The answers to these questions are quite complex and involve many different factors. First, it is important to understand that changes in glaciers do not only depend on temperatures, but also on precipitation, cloud cover, relative humidity and the intensity of solar irradiation. And in the case of temperatures, summer temperatures (rainy season) are more important than winter temperatures (dry season), and daytime temperatures are more important than night time temperatures. In Figure 2 above, we see that winter temperatures have fallen more strongly than summer temperatures (the average winter anomaly is -0.9ºC while average summer anomaly is -0.4ºC). Since winter is the dry season in this region, colder winter temperatures will have little effect on the glaciers because temperatures are already well below freezing. In contrast, warmer summer temperatures can have a dramatic effect. It was the unusually hot and dry summer of 1998 (the Mega-El Niño) which caused the permanent closing of the Chacaltaya ski-resort, and the four consecutive warm summers of 2002, 2003, 2004 and 2005 almost completely eliminated the glacier. A meteorologist from the Hadley Climate Research Centre suggested to me that the likely explanation for the observed decrease in temperatures in the Bolivian highlands is a decrease in low level clouds. With fewer low level clouds, night time temperatures would tend to fall substantially (due to increased outgoing infra-red radiation), which would pull down average temperatures. During the day, fewer clouds would have a positive effect on temperatures, increase solar irradiation reaching the ice, and decrease air humidity and precipitation, all of which would contribute to speed up melting, despite stronger night time cooling. I could not find specific data on cloud cover in the Bolivian highlands, but worldwide low level cloud cover has clearly decreased since about 1987 (see Figure 3). According to NASA/GISS the decrease is particularly strong in the tropics, including Bolivia (3) 4, so the meteorologist's hunch is likely to be correct.
The decrease in cloud cover is related to decreases in precipitation, which has had a large influence on the fate of the Chacaltaya glacier. The increase in the glacier regression rate since the end of the 1970s appears to coincide with the Great Pacific Shift of 1976, after which precipitation has decreased systematically, both according to direct measurements at the La Paz/El Alto station, and according to precipitation proxy series generated from ice cores from two other Bolivian glaciers (4) 6. If the rapid melting of Chacaltaya since the mid 1970s were caused by increasing temperatures due to increased CO2 in the atmosphere, we would have observed increased night time temperatures, increased average temperatures, and increases in cloud cover and precipitation (that is what CO2 driven climate models would suggest). But instead we have observed decreasing cloud cover, decreasing average temperatures (likely the result of night time temperatures falling more than day time temperatures increased), and decreasing precipitation, all of which conspired to melt the glacier. The observed evidence from Chacaltaya is thus inconsistent with the Anthropogenic Greenhouse Warming (AGW) theory, or, at least, if there is an AGW signal, it is completely drowned by other climatic changes unrelated to AGW. It is ironic that the melting Chacaltaya glacier has become such an important symbol of the AGW theory, when in fact the evidence from Chacaltaya seems to refute this theory. (In contrast, the evidence from Chacaltaya is fully consistent with Svensmark's cosmic ray theory (5) 7, but that is another story). How can Bolivia be cooling down while its glaciers melt? Leave a reply below. Lykke Andersen is the Director of the Center for Economic and Environmental Modeling and Analysis (CEEMA) at INESAD. (1) Figure 1 of this newsletter is a reproduction of Figure 1.1 of the IPCC Fourth Assessment Report from Working Group 2. It has been reproduced countless times before in climate change studies and presentations all over the world. |
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