Black carbon aerosols and the third polar ice cap

Abstract

Abstract. Recent thinning of glaciers over the Himalayas (sometimes referred to as the third polar region) have raised concern on future water supplies since these glaciers supply water to large river systems that support millions of people inhabiting the surrounding areas. Black carbon (BC) aerosols, released from incomplete combustion, have been increasingly implicated as causing large changes in the hydrology and radiative forcing over Asia and its deposition on snow is thought to increase snow melt. In India BC from biofuel combustion is highly prevalent and compared to other regions, BC aerosol amounts are high. Here, we quantify the impact of BC aerosols on snow cover and precipitation from 1990 to 2010 over the Indian subcontinental region using two different BC emission inventories. New estimates indicate that Indian BC from coal and biofuel are large and transport is expected to expand rapidly in coming years. We show that over the Himalayas, from 1990 to 2000, simulated snow/ice cover decreases by ~0.9% due to aerosols. The contribution of the enhanced Indian BC to this decline is ~30%, similar to that simulated for 2000 to 2010. Spatial patterns of modeled changes in snow cover and precipitation are similar to observations (from 1990 to 2000), and are mainly obtained with the newer BC estimates.

Black carbon aerosols over the Himalayas: direct and surface albedo forcing

“…Generally, climate model simulations of BC-induced snow darkening have revealed significant consequences on regional climate and hydrological cycles during the pre-monsoon season (Menon et al, 2010;Qian et al, 2011). However, it is very difficult to simulate the aerosol fields over complex and high terrain and most of the climate models simulate very low BC concentration in the atmosphere over south Asia especially over the Indian region (Ganguly et al, 2009;Menon et al, 2010;Nair et al, 2012).…”

“…The day-today lives of millions of people, their agricultural practices and their economy are directly or indirectly controlled by the monsoon rainfall and the river discharges fed by the Himalayan glaciers (Vaux et al, 2012). Even though there are several geological and glaciological reasons for the retreat or advance of glaciers over the Himalayas (Bolch et al, 2012), surface darkening due to BC deposition is being increasingly projected by modelling studies as a major factor contributing to the faster snow melting (Flanner et al, 2009;Menon et al, 2010;Qian et al, 2011) and several caveats have been put forward. Recently, BC-induced free-tropospheric heating (elevated heat pump) (Lau et al, 2006) and snow-albedo reduction due to BC deposition over the Himalayan region (Qian et al, 2011) has received significant scientific attention because of its projected implications on the regional climate, monsoon and hydrological cycle (Nigam and Bollasina, 2010).…”

“…In addition to the direct radiative interaction with solar and terrestrial radiation via scattering and absorption, BC aerosols modify the cloud microphysical properties (indirect and semi-direct effect) and reduce the albedo of the snow due to BC deposition Flanner et al, 2007;IPCC, 2007). The radiative forcings due to direct, semi-direct and snow-albedo effects of BC aerosols and their implications on the hydro-climate are amongst the major challenges in the regional climate impact assessments (Flanner et al, 2007;Menon et al, 2010;Nigam and Bollasina, 2010).…”

“…However, it is very difficult to simulate the aerosol fields over complex and high terrain and most of the climate models simulate very low BC concentration in the atmosphere over south Asia especially over the Indian region (Ganguly et al, 2009;Menon et al, 2010;Nair et al, 2012). Even though aerosol BC over the Himalayas, in general, and glaciers in particular, have been a topic of prime scientific interest, there are not much measurements of BC over the western and southern slopes of the Himalayas, while measurements of BC on snow have been reported from several locations on the Tibetan plateau and southeastern Himalayas (Ming et al, 2008(Ming et al, , 2009Xu et al, 2009;Huang et al, 2011).…”

Absorbing aerosol in the troposphere of the Western Arctic during the 2008 ARCTAS/ARCPAC airborne field campaigns

“…Reductions in snow and ice albedo is of particular concern because of its positive feedback on melting of seasonal snow cover at mid-latitudes (Flanner et al, 2009), permanent snow and ice at high altitude (Menon et al, 2010;Xu et al, 2009) and in the polar regions (Hansen and Nazarenko, 2004).…”