Over the past three months this blog has reviewed some of the current literature on Himalayan glaciers in an attempt to understand how they are projected to respond to climate change. Drawing upon research using a variety of methods from proxy records to modelling some general trends are apparent.
The overall consensus within the literature is that substantially more research is needed (ICIMOD, 2011). Although the Himalayan region contains the greatest volume of ice and snow outside of the polar region (Kulkarni 1991), research has mainly been conducted on accessible glaciers generally in lower altitude regions. Of the 54,000 glaciers distributed within the Himalayan region, a comprehensive report by the ICIMOD (2011) in the Hindu-Kush Himalaya suggested that long-term field-based monitoring of glacial mass changes had only occurred on around a dozen glaciers. While remote sensing is increasingly being used to substitute for the lack of data, these images still require ground-truthing for validation. Therefore, although some general trends are apparent, significantly more research is required underlined by the complex spatial variability across the region.
MAJOR FINDINGS
Paleoclimatic records of past wamer interglacials periods including the Eemian (MIS 5e) and the Holsteinian (MIS 11) suggest that the current average global temperature is not unprecedented on a geological timescale (Hanson and Sato, 2011). Proxy records have indicated glacier extent in the Himalayas have also varied in the past responding to natural forcings from solar radiation and volcanic activity. However, it is not the level of warming that is the main concern but the rate of warming during the twentieth century. Crowley (2000) claims only 25% of the twentieth century warming could be accounted for by natural variability, with anthropogenic factors forcing climate variability. This is a major concern in predicting future climate change as some anthropogenic inputs into the Earths systems such as black carbon are the product of human activity and therefore are absent from the historical record. Therefore understanding the direct and indirect effects are restricted to limited short-term instrumental studies resulting in high uncertainty in predictions of future climate change and its impacts on the glacial system.
Concurring with the overall trend around the world, glaciers in the Himalayas have generally been in a state of decline since the beginning of the twentieth century (IPCC, 2007). Some studies have also suggested that the rate of retreat in the Himalayas is two to eight times greater than the global average (Shrestha et al., 1999) attributed, in part, to additional regional forcing including atmospheric brown clouds (ABCs), surface darkening by black carbon (BC) and changes to the Asian monsoon (Li et al., 2011). These regional forcings result cause notable signatures in the response of Himalayan glaciers to climate change, adding to the spatial complexity across the mountain chain.
Overall, glaciers in the Himalayan region have been in a state of retreat since the beginning of the twentieth century. In addition to global rises in temperatures, regional forcing have resulted in complex spatial variability in the rate of retreat of glaciers across the region with greater declines in glacial extent reported in the monsoon-dominated southern and eastern Himalayan regions (ICIMOD, 2011). However, it is widely acknowledge that this general trend cannot be applied to all glaciers within the Himalayas. Research by Hewitt (2005; 2011) and Scherler (2011) have illustrated that glaciers in the Karakoram region are mainly static or advancing in some areas. This underlines the complexity of the atmospheric-land interactions feedbacks within the region, resulting in highly individualistic responses to climate change depending on current glacial extent and thickness, the presence or absence of debris, elevation and the dependence on the glacier on monsoon as a source of precipitation.
IMPACTS ON HIMALAYAN COMMUNITIES
Supplying 1.3 billion people with freshwater, the Himalayas are frequently referred to as the ‘Water Towers of Asia’ (ICIMOD, 2011). The lack of data and spatial complexity in the region make attempts to predict and mitigate against climate change particularly difficult as general trends cannot be applied across the region. Changes to glaciers within the Himalayas are likely to have numerous direct and indirect impacts on the communities that occupy the mountain region and surrounding lowland areas, occurring on a continuum of spatial and temporal scales. In the short term, increased glacial melt in projected to increase the frequency and magnitude of glacial lake outburst floods (GLOFs) and, assuming negligible changes in precipitation increase river discharge in glaciated river basins. However, shifts in the hydrological regime indicate that the buffering effect of the glacial component augmenting periods of low flow during years of failed or weakened monsoons may be reduced (Thayyen and Gergan, 2010). In the long term, under the business-as-usual scenario the discharge of rivers such as the Ganges with their headwaters in Himalayas are projected to decrease increasing water scarcity in the region (Rees and Collins, 2006).
CONCLUSIONS
Viewed within a context of increased development and growing population in the region, understanding the response of glaciers to climate change is essential in order to effectively manage against increased hazards and reduce water stress within the region. Climate change is likely to cause substantial changes to glaciers within the Himalayan region and worldwide. Although the IPCC (2007) projection may have been an overexaggeration it is widely acknowledged that under the the business-as-usual scenario most Himalayan glaciers are likely to disappear within the 21st century. Unless stricter measures are put in place, irreversible changes could result with severe socio-economic consequences. Alterations to the extent of these ice giants could have significant impacts on ecosystems, human society and most significantly, the dynamics the Earths system, and therefore maintaining glaciers is fundamentally important if we are to maintian the world as we know it.
Reference
Crowley, T. J. (2000) 'Causes of climate change over the past 1000 years', Science, 289: 270-277.
Hanson, J. E. and M. Sato (2011) Paleoclimate Data for Human-made Climate Change, NASA Goddard Institute for Space Studies: New York, 1-32.
Hewitt, K (2005) ‘The Karakoram anomaly? Glacier expansion and the ‘Elevation effect,’ Karakoram Himalaya.’ Mountain Research and Development 25,4,: 332-340
Hewitt, K. (2011) 'Glacier change, concentration, and elevation effects in the Karakoram Himalaya, upper Indus Basin', Mountain Research and Development , 31: 188-200
IPCC (2007) Climate Change 2007: Impacts, Adaptation and Vulnerability, in M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (Eds) Contributions of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press: Cambridge.
Kulkami, A. V (1991) ‘Glacier inventory in Himachal Pradesh using satellite data.’ Journal of Indian Society of Remote Sensing,19,3: 195-203
Li, Z., Y. He, W. An, L. Song, W. Zhang, N. Catto, Y. Wang, S. Wang, H. Lui, W. Cao, W. H. Theakstone, S. Wang and J. Du (2011) ‘Climate change and glacier changes in southwestern China during the past several decades’, Environmental Research, 6,4: 1-25.
The overall consensus within the literature is that substantially more research is needed (ICIMOD, 2011). Although the Himalayan region contains the greatest volume of ice and snow outside of the polar region (Kulkarni 1991), research has mainly been conducted on accessible glaciers generally in lower altitude regions. Of the 54,000 glaciers distributed within the Himalayan region, a comprehensive report by the ICIMOD (2011) in the Hindu-Kush Himalaya suggested that long-term field-based monitoring of glacial mass changes had only occurred on around a dozen glaciers. While remote sensing is increasingly being used to substitute for the lack of data, these images still require ground-truthing for validation. Therefore, although some general trends are apparent, significantly more research is required underlined by the complex spatial variability across the region.
MAJOR FINDINGS
Paleoclimatic records of past wamer interglacials periods including the Eemian (MIS 5e) and the Holsteinian (MIS 11) suggest that the current average global temperature is not unprecedented on a geological timescale (Hanson and Sato, 2011). Proxy records have indicated glacier extent in the Himalayas have also varied in the past responding to natural forcings from solar radiation and volcanic activity. However, it is not the level of warming that is the main concern but the rate of warming during the twentieth century. Crowley (2000) claims only 25% of the twentieth century warming could be accounted for by natural variability, with anthropogenic factors forcing climate variability. This is a major concern in predicting future climate change as some anthropogenic inputs into the Earths systems such as black carbon are the product of human activity and therefore are absent from the historical record. Therefore understanding the direct and indirect effects are restricted to limited short-term instrumental studies resulting in high uncertainty in predictions of future climate change and its impacts on the glacial system.
Concurring with the overall trend around the world, glaciers in the Himalayas have generally been in a state of decline since the beginning of the twentieth century (IPCC, 2007). Some studies have also suggested that the rate of retreat in the Himalayas is two to eight times greater than the global average (Shrestha et al., 1999) attributed, in part, to additional regional forcing including atmospheric brown clouds (ABCs), surface darkening by black carbon (BC) and changes to the Asian monsoon (Li et al., 2011). These regional forcings result cause notable signatures in the response of Himalayan glaciers to climate change, adding to the spatial complexity across the mountain chain.
Overall, glaciers in the Himalayan region have been in a state of retreat since the beginning of the twentieth century. In addition to global rises in temperatures, regional forcing have resulted in complex spatial variability in the rate of retreat of glaciers across the region with greater declines in glacial extent reported in the monsoon-dominated southern and eastern Himalayan regions (ICIMOD, 2011). However, it is widely acknowledge that this general trend cannot be applied to all glaciers within the Himalayas. Research by Hewitt (2005; 2011) and Scherler (2011) have illustrated that glaciers in the Karakoram region are mainly static or advancing in some areas. This underlines the complexity of the atmospheric-land interactions feedbacks within the region, resulting in highly individualistic responses to climate change depending on current glacial extent and thickness, the presence or absence of debris, elevation and the dependence on the glacier on monsoon as a source of precipitation.
IMPACTS ON HIMALAYAN COMMUNITIES
Supplying 1.3 billion people with freshwater, the Himalayas are frequently referred to as the ‘Water Towers of Asia’ (ICIMOD, 2011). The lack of data and spatial complexity in the region make attempts to predict and mitigate against climate change particularly difficult as general trends cannot be applied across the region. Changes to glaciers within the Himalayas are likely to have numerous direct and indirect impacts on the communities that occupy the mountain region and surrounding lowland areas, occurring on a continuum of spatial and temporal scales. In the short term, increased glacial melt in projected to increase the frequency and magnitude of glacial lake outburst floods (GLOFs) and, assuming negligible changes in precipitation increase river discharge in glaciated river basins. However, shifts in the hydrological regime indicate that the buffering effect of the glacial component augmenting periods of low flow during years of failed or weakened monsoons may be reduced (Thayyen and Gergan, 2010). In the long term, under the business-as-usual scenario the discharge of rivers such as the Ganges with their headwaters in Himalayas are projected to decrease increasing water scarcity in the region (Rees and Collins, 2006).
CONCLUSIONS
Viewed within a context of increased development and growing population in the region, understanding the response of glaciers to climate change is essential in order to effectively manage against increased hazards and reduce water stress within the region. Climate change is likely to cause substantial changes to glaciers within the Himalayan region and worldwide. Although the IPCC (2007) projection may have been an overexaggeration it is widely acknowledged that under the the business-as-usual scenario most Himalayan glaciers are likely to disappear within the 21st century. Unless stricter measures are put in place, irreversible changes could result with severe socio-economic consequences. Alterations to the extent of these ice giants could have significant impacts on ecosystems, human society and most significantly, the dynamics the Earths system, and therefore maintaining glaciers is fundamentally important if we are to maintian the world as we know it.
Reference
Crowley, T. J. (2000) 'Causes of climate change over the past 1000 years', Science, 289: 270-277.
Hanson, J. E. and M. Sato (2011) Paleoclimate Data for Human-made Climate Change, NASA Goddard Institute for Space Studies: New York, 1-32.
Hewitt, K (2005) ‘The Karakoram anomaly? Glacier expansion and the ‘Elevation effect,’ Karakoram Himalaya.’ Mountain Research and Development 25,4,: 332-340
Hewitt, K. (2011) 'Glacier change, concentration, and elevation effects in the Karakoram Himalaya, upper Indus Basin', Mountain Research and Development , 31: 188-200
IPCC (2007) Climate Change 2007: Impacts, Adaptation and Vulnerability, in M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (Eds) Contributions of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press: Cambridge.
Kulkami, A. V (1991) ‘Glacier inventory in Himachal Pradesh using satellite data.’ Journal of Indian Society of Remote Sensing,19,3: 195-203
Li, Z., Y. He, W. An, L. Song, W. Zhang, N. Catto, Y. Wang, S. Wang, H. Lui, W. Cao, W. H. Theakstone, S. Wang and J. Du (2011) ‘Climate change and glacier changes in southwestern China during the past several decades’, Environmental Research, 6,4: 1-25.
Scherler,D; Bookhagen, B; Strecker,MR (2011) Spatially variable response of Himalayan glaciers to climate change affected by debris cover. Nat. Geosci. 4:156-159,doi:10.1038/NGEO1068, 2572,2583
Shrestha, A. B., C. P. Wake, P.A. Mayewski and J.E. Dibb (1999) ‘Maximum temperature trends in the Himalaya and its vicinity: An analysis based on temperature records from Nepal for the period 1971-94.’ Journal of Climate, 12: 2775-2767
Thayyen, R. J., and J. T. Gergan (2010) ‘Role of glaciers in watershed hydrology: a preliminary study of a “Himalayan catchment”, The Cryosphere, 4: 115-128.
Shrestha, A. B., C. P. Wake, P.A. Mayewski and J.E. Dibb (1999) ‘Maximum temperature trends in the Himalaya and its vicinity: An analysis based on temperature records from Nepal for the period 1971-94.’ Journal of Climate, 12: 2775-2767
Thayyen, R. J., and J. T. Gergan (2010) ‘Role of glaciers in watershed hydrology: a preliminary study of a “Himalayan catchment”, The Cryosphere, 4: 115-128.
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