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>Recent changes in freezing level heights in the Tropics withimplications for the deglacierization of high mountain regions
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Recent changes in freezing level heights in the Tropics withimplications for the deglacierization of high mountain regions
The height of the freezing level in the tropicalatmosphere(the free air 0°C isotherm)has increasedacross most of the region,particularly in the outerTropics. In the tropical Andes,south of the Equator, highelevation surface temperatures and upper air data show asimilar trend in temperature,of～0.1°C/decade over the last50 years. Meteorological observations at 5680 m on thesummit of the Quelccaya Ice Cap,the largest ice mass in theTropics,indicate that daily maximum temperatures oftenexceed 0°C from October-May,and rise well abovefreezing for much of the year around the ice cap marginat 5200 m. This is consistent with observations of a rise inthe percolation facies (an indicator of surface melting)inrecent decades,and other observations of marginalrecession,showing that the ice cap is rapidly losing mass.Similar conditions are likely to be affecting other highelevation ice caps and glaciers in Ecuador,Peru and Bolivia,with important implications for water supplies in the region.Over the Tropics as a whole,freezing level height(FLH)isclosely related to mean SSTs,with inter-annual variations inFLH controlled by the phase of ENSO variability.Moreextensive monitoring of climatic conditions at highelevations in the mountains of the Tropics is urgentlyneeded.
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