Global warming is on the increase claim the protagonists of the threat. Blames and counter blames are being traded between the developed and developing nations. How much the humanity is responsible for this 'global warming' (which the author prefers to call as the climate shift) is a matter of debate and investigation. But yes the nature has been doing it since the earth came in to being; there have been episodes of extreme global warming and cooling.
Since the last ice age about 18K years ago we are living in an inter-glacial period, which is a period of warming. It is the interlude when life in every form thrives on the earth. The heat may not suit some organisms including the humans, but it does help many others to proliferate, like the insects.
The climatologists claim that in the past one century, there has been an overall increase in surface temperature by about 0.5 to 1.1 degrees centigrade. Ten warmest years have been felt after 1860 and the two decades after 1980 have proved to be the warmest. The heat is on. Our earth is a part of the solar system. The planets of the system have impacts on each other. The solar variability is one of the reasons of change in temperatures as the Sun is our main source of energy. Solar flares, changes in orbit etc are many factors that do affect the temperatures on the urban planet. Volcanic eruptions are yet another major causative factor for the rise in the surface temperatures of the earth.
These two major factors have been contributing to the earth's temperatures since times immemorial. Of course they were never like only heaters-there have been many periods of the earth's history when everything was frozen. Therefore, heating and cooling have been two sides of the same coin that is, the environment of the earth. Alas since the emergence of man on this urban Planet, his changing ways of living are believed to be another major cause of climate shift. In fact the human interference with the nature has become so intense that some scientists have coined the term 'Anthropocene' for the latest chapter of the Earth's history. There is no starting date for this chapter, but 18th century, when James Watt invented his steam engine in 1784 is taken to be the beginning. Paul Curzon, the Nobel Prize winner for Chemistry in 2000 had coined this term and it seems to stay on!
One of the worst impacts of humans on this planet has been in the form of accelerating the pace of rise in temperature. Many experts believe that more than 90% of the recent rise in temperatures is due to anthropogenic reasons, say M. R. Bhutiyani of College of Military Engineering, Pune and Vishwas S. Kale and N.J. Pawar of University of Pune, in Current Science (September, 2008).
The climatologists all over the globe have been collecting the evidences for rise in temperatures. Swiss and French Alps, Rocky Mountains, Colorado and across the US, Europe and Antarctica have provided clear indications of rise in temperature during the 20th century say Bhutiyani and his co-researchers. The former Soviet Union except in eastern Siberia, the Baltic Republics, some locations in Caucasus and at low elevations in Central Asia show a rising trend. The rise in temperature has been felt almost in every region.
Climatological studies reveal that India has shown a warming of 0.4 degrees Celsius up to the late 1980s. In general the pattern of air temperatures over the sub-continent shows a similarity with the global trend say Bhutiyani and his colleagues. Nepal and Uttarakhand Himalayas have also shown a rise in temperature, but with a difference that in some portions of western Himalayas a pre-monsoon cooling has been observed from March to May. The Himalayas are the 'climate makers for the Asia. Part falling within the Indian Territory being rugged has a sparse network of gauging sites to measure the water discharge of the rivers and stream flow patterns. As a result some parts of North West Himalayas (NWH) are the gap areas of the climate history. Taking Satluj River basin as one of the key areas, Bhutiyani and his colleagues have tried to fill in theses gaps.
An increase or decrease in the river discharge is one of the strongest evidences for climate change. As already said NWH has gap areas as far as climate data is concerned. But thanks to our past leaders who took up harnessing of the rivers like Satluj, Chenab and Beas for power generation. Before a river is harnessed with the help of dams, the discharge data of the river is collected meticulously. In the instant case the researchers were lucky to have got the discharge data of Ravi, Chenab, Beas and Satluj rivers for the period ranging from 1912 to 2004 from various sources like Bhakra-Beas Management Board, Indus Treaty Commissioner, Himachal Pradesh Electricity Board etc.
Bhutiyani and his team resorted to complex statistical methods to find out the changes in the stream-flow over a period of time. Earlier studies by G.B. pant et al of Indian Institute of Tropical Meteorology, Pune and Bhutiyani et al in the area had enough evidences to prove that the air temperature in the NWH had risen @ 1.6 degrees Celsius per 100 years in the last century. This rate is much higher compared with 0.5 to 1.1 degrees Celsius rise in the global air temperature. What is alarming is that the winters in the last two decades have shown unusual rise of 4.4 degrees Celsius in average temperatures. Under normal circumstances there was a set pattern of precipitation during the monsoon and winters. This added to the snow cover. Now the rate of melting has become variable say Bhutiyani et al. Accordingly, in some portions of NWH melting of glaciers is higher and in others it is normal. In areas where the rate of melting is higher the discharge of the rivers is affected.
As per their study while the Satluj River shows increase or decrease in discharge during the monsoon months in the period from 1922-2004, the other rivers like Beas and Ravi rivers have comparatively fewer glaciers hence show hardly any variation in their discharges. Satluj and Chenab basins have a large number of glaciers and these rivers have shown sudden changes in their discharges. Consequently, there has been an increase of high magnitude floods in these rivers. We have already about the unprecedented floods in Satluj River (A Country Deluged)
The recent floods in Kosi are again a pointer towards unprecedented behavior of the snow-fed rivers. The climate shift can cause higher melting of glaciers, heavier snowfall in early winters, heavy rainfall in the pre-monsoon months can all change the rivers discharge and bring misery in the downstream areas. The lower reaches of the rivers of NWH referred here are densely populated, agriculturally fertile and industrially developing. As such floods in these rivers can cause greater damage to life and property.
The study carried out by Bhutiyani et al is just an indicator of the likely events that can take place anytime particularly in the Himalayan foot hills. There is an acute need to study in detail the entire river basins and constantly monitor the mass balance studies of the glaciers to avert a mishap if any.