Himalayan glaciers [image credit: earth.com]
Time to dial down some over-excitable climate claims perhaps. The actual mechanism has been observed elsewhere before, but ‘not all downslope winds are katabatic‘. Effects can vary according to local conditions.
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Himalayan Glaciers fight back to preserve themselves, but for how long? — asks Eurekalert.
An international team of researchers, co-led by Professor Francesca Pellicciotti of the Institute of Science and Technology Austria (ISTA), explains a stunning phenomenon: rising global temperatures have led Himalayan glaciers to increasingly cool the air in contact with the ice surface.
The ensuing cold winds might help cool the glaciers and preserve the surrounding ecosystems. The results, found across the Himalayan range, were published in Nature Geoscience.
Is global warming causing Himalayan glaciers to melt like ice cream on a hot summer day? Previously, scientists documented an elevation-dependent warming effect: they showed that mountain tops “felt” the effect of global warming stronger and warmed up faster.
Yet, a high-altitude climate station at the base of Mount Everest in Nepal showed an unexpected phenomenon: the measured surface air temperature averages remained suspiciously stable instead of increasing. How could this data be interpreted?
The Pyramid International Laboratory/Observatory climate station, located at a glacierized elevation (5050 m) on the southern slopes of Mount Everest, alongside the Khumbu and Lobuche glaciers, has continuously recorded hourly meteorological data for nearly three decades.
Now, an international team of researchers led by new ISTA Professor Francesca Pellicciotti and National Research Council of Italy (CNR) researchers Franco Salerno and Nicolas Guyennon cracked the code.
The warming climate is triggering a cooling reaction in the glaciers: it is causing cold winds—katabatic winds—to flow down the slopes. But how long can the glaciers locally counterbalance the effects of global warming by cooling themselves? And which characteristics allow the glaciers to do so?
The Devil Is in the Detail
To explain the observed phenomenon, the team had to examine the data thoroughly. “We found that the overall temperature averages seemed stable for a simple reason. While the minimum temperatures have been steadily on the rise, the surface temperature maxima in summer were consistently dropping,” says Salerno. The glaciers are reacting to the warming climate by increasing their temperature exchange with the surface, Pellicciotti explains.
Global warming causes an increased temperature difference between the warmer environmental air over the glacier and the air mass in direct contact with the glacier’s surface. “This leads to an increase in turbulent heat exchange at the glacier’s surface and stronger cooling of the surface air mass,” says Pellicciotti. As a result, the cool and dry surface air masses become denser and flow down the slopes into the valleys, cooling the lower parts of the glaciers and the surrounding ecosystems.
What Makes Glaciers Fight Back?
Going beyond the ground observations uniquely available at Pyramid, the team drew on the latest scientific advances in climate models: the global climate and weather reanalysis called ERA5-Land. ERA5-Land reanalysis combines model data with observations from across the world into a globally complete and consistent dataset using the laws of physics.
Interpreting this data allowed the team to demonstrate that the global warming-induced katabatic winds occurred not only on Mount Everest but in the entire Himalayan range.
“This phenomenon is the outcome of 30 years of steadily increasing global temperatures. The next step is to find out which key glacier characteristics favor such a reaction,” says Pellicciotti.
Full article here.
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December 5, 2023 at 01:39PM
Iowa Climate Science Education 