Two-tiered reconstruction of Late Pleistocene to Holocene changes in the freezing level height in the largest glacierized areas of the Colombian Andes

One way of deducing vertical shifts in the altitudinal distribution of Colombian high-altitude páramo environments is by inferring fluctuations in the height of the local freezing level.In our research,we are implementing two complementary approaches to reconstruct Late Pleistocene to Holocene changes in the freezing level height(FLH)in two of the most extensively glacier-covered areas of the northern Andes.We combined remote sensing and field-based geomorphological mapping with time-series reconstruction of changes in the altitude of the 0°C isotherm.Changes in the FLH were based on alreadypublished~30 kyr paleo-reconstructions of sea surface temperatures(SSTs)of the eastern tropical Pacific and the western tropical Atlantic,as well as on reconstructed long-term sea level changes and empirical orthogonal functions of present-day(historical)Indo-Pacific and tropical Atlantic SST anomalies.We also analyzed the probability distribution of air-sea temperature differences and the spatial distribution of grid points with SSTs above the minimum threshold necessary to initiate deep convection.We considered available historical nearsurface and free air temperature data of ERA-Interim reanalysis products,General Circulation Model(GCM)simulations,weather stations,and(deployed by our group)digital sensors,to assess the normal Environmental Lapse Rates(ELRs)at the regional to local scale.The combined maps of glacial landforms and our reconstructed FLHs provided us with a wellfounded inference of potential past glacier advances,narrowing down the coarse resolution of ice margins suggested by previous research efforts.The extent of the areas with temperatures below the freezing point suggested here for the summits of our main study site exceeds in magnitude the corresponding glacier icecaps and front advances proposed by previous studies.Conversely,our average lowest altitudes of the FLH for our comparative site are consistently above the main glacier-front advances previously suggested.Our results indicate that,compared to the maximum upward changes that likely took place over the past ca.20,000 years in our two areas of interest,the observed(present-day)upward shifts of the FLH have occurred at a rate that significantly surpasses our inferred rates.Our study helps fill the gaps in understanding past climatic changes and present trends in the region of interest and provides some insights into analyzing the signals of natural and anthropogenic climate change.

Variability of atmospheric freezing level height derived from radiosonde data in China during 1958-2005 and its impact to cryosphere changes

Atmospheric air temperature data from 92 stations in China＇s radiosonde network were used to analyze changes in the freezing level height （FLH）, glacier snow line, and ice edge from 1958-2005 （48 years） and to examine the impact of these changes on the cryosphere. In general, the FLH, glacier snow line, and ice edge exhibited latitudinal zonation, declining from south to north. Trends in the FLH, glacier snow line, and ice edge showed spatial heterogeneity during the study period, with prevailing upward trends. Temporally, the FLH, glacier snow line, and ice edge trends differed on various time scales.