WARM HIMALAYAS- PROF. SYED IQBAL HASNAIN
Glaciers in the Himalayas are fast retreating like other ice mountains the world over. A recent study showed that the last three decades of 21stcentury have been the hottest period in 1,000 years. The melting of the Gangotri glacier is accelerating at an average retreat rate of 30 metres annually.
The main reason for deglaciation the world over is global warming. The atmospheric levels of the greenhouse gas carbon dioxide have increased since pre-industrial times. Levels of atmospheric methane, another powerful greenhouse gas, have risen in the last 100 years.
Greenhouse gases such as nitrous oxide and carbon dioxide in the Earth’s atmosphere decrease the escape of terrestrial thermal infrared radiation. Increasing carbon dioxide, therefore, effectively increases radiative energy to the Earth. But what happens to this radiative input is complex: it is redistributed by various physical processes.
The positive radiative input tends to warm the surface, lower atmosphere. More of the outgoing terrestrial radiatives from the surface of the Earth is absorbed by the atmosphere and re-emitted at higher altitudes at lower temperature. This results in a positive radiative input that tends to warm the lower atmosphere and surface. This directly causes for the retreat of glaciers.
Anthropogenicgeenhouse gas emission levels depend on the human population size, the level of economic activity, and the technologies in use. Increases in population and level of economic activity tend to be closely tied to increased use of energy. Insofar as fossil fuels are used as the source of this energy, increased use of energy will lead to increased carbon dioxide emissions unless sequestration, energy efficiency improvements, or other technologies can balance it.
In addition to this, aerosol, a long recognized major environmental hazard, is also now known to have strong impacts on South and East Asian climates. The presence of aerosols profoundly affects the water cycle. Through this ‘direct effect’, aerosol scatters and absorbs solar radiation, thus cooling the earth surface and changing the horizontal and vertical heating contrast in the atmosphere.
The heating contrast drives anomalous atmospheric circulation, resulting in changes in convection, clouds and rainfall.
Another way aerosol can affect the water cycle is through the so-called ‘indirect effects,’ whereby aerosol increases the number of cloud condensation nuclei, prolongs lifetime of clouds, and inhibits the growth of cloud-drops to raindrops. This leads to more clouds, and increased reflection of solar radiation, and further cooling on the Earth’s surface.
The direct impact of greenhouse gas emission and resultant global warming on the glacier environment is melting. There are different reasons for ice melting. Its repercussions are also different, depending on regional and climatic variables. Flood, sea level rise, fresh water scarcity, threat to fauna and flora are major security implications of deglaciation.
With an estimated contribution of 0.2-0.4mm per year from melting glaciers, the average global sea level rose by 1-2mm per year during the 1990s. It is expected that the melting ice from ice caps and glaciers will raise sealevels between 10 and 90 cms in the 21st century. It is observed that about 20,000 years ago, the sea level was 25 metres lower than it’s today.Sea-level rise will affect coastal region throughout the world, causing flooding, erosion, and saltwater intrusion into aquifers and freshwater habitats.
In short, the deglaciation in the Himalayas is influenced by various factors, climatic, regional etc. However, the main underlying factor is ever increasing warming on the mountains, chiefly because of excess emission of greenhouse gases and Asian brown cloud. The ongoing ice melting is only the tip of the iceberg that will hit us in the near future.