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Conference on Climate Change: Shifting Science and Changing Policy

 

14 October 2011

Phirozeshah Mehta Building , Mumbai University ,

Vidyanagari, Kalina, Mumbai

Session 1: Climate Science
  • Welcome: Prof Mugdha Karnik, Director, Centre for Extra Mural Studies
  • Inauguration: Prof S. B. Chaphekar, former head of the department of environmental sciences, University of Pune
  • Prof. R. R. Kelkar: India's Climate Change Concerns and the Need for Better Climate Models (Read Abstract)
  • Dr. Madhav Khandekar: Indian Monsoon Variability in the context of Global Warming Debate (Read Abstract)

Abstracts of papers to be presented in session on Climate Science.

India’s Climate Change Concerns and the Need for Better Climate Models

 

By:  Prof. R.R. Kelkar

 

India is a vast country with a billion-plus population and it has a variety of climates and topographical features. It depends on the monsoons for meeting all its water needs, with its major rivers either originating from the Himalayas or fed by the monsoon rains. Indian agriculture is critically linked to weather and climate. India has faced severe droughts, widespread floods and devastating tropical cyclones. The threat of climate change induced by global warming therefore looms large over India in a real sense. Although this problem has global dimensions, there are certain challenges that are specific to India. It would also like to ensure that the mitigation actions do not themselves become a stumbling block in the path of sustainable development.

 

India has reason to be concerned about the likely impacts of climate change on at least six major fronts:

  • Change in the amount and distribution pattern of monsoon rainfall, which is India’s only source of water
  • Effect of temperature rise and change in the rainfall pattern on agricultural production and its impact on food security
  • Possible increase in the frequency and intensity of tropical cyclones over the Bay of Bengal and Arabian Sea, which cause heavy losses of life and property in the coastal regions
  • Threat of sea level rise to India’s 7,500 km long coastline including the Andaman, Nicobar and Lakshadweep islands
  • Retreat of Himalayan glaciers and its effect on the Indian rivers which originate in the Himalayas
  • The possible effect on the health of the population arising from the growth of vector-borne diseases due to rising temperatures

Monsoons: Many investigations have addressed the above concerns using global climate models. Since India is a country of sub-continental dimensions and phenomena like the Indian monsoon are a major component of the global atmospheric circulation system, it is not illogical to use global models for this purpose and many significant results have indeed been obtained about likely climate change over India. However, it has to be accepted that global models have a coarse resolution of 250 to 500 km and the results cannot bring out the finer features such as orography-induced rainfall. Moreover, monsoon processes show up quite differently in different climate models. In fact, several global models have not even been able to capture the basic climatology of the Indian monsoon on either spatial or temporal scales or both. This casts a shadow of doubt on the projected anomalies of temperature and rainfall when the mean values are themselves uncertain. Paradoxically, many models indicate a weakening of the monsoon circulation but an intensification of the rainfall and an extension of the monsoon season. The projected increase in monsoon precipitation has a wide difference across models, ranging from 3 to 17 %.

 

The only regional model used in climate change assessments over India is the Hadley Centre’s high-resolution (50 km) regional climate model, PRECIS (Providing Regional Climates for Impact Studies). The results that have become available as recently as in August 2011 are again not free from uncertainty. They provide more of a qualitative direction than a quantitative estimate, and the experiments need to be repeated with multiple emission scenarios and multiple models. The indications are that the summer monsoon precipitation over India may be 9 to 16% more in the 2080s compared to the 1970s, but the rainfall may in fact decrease over some regions of the country. Also, the rainfall distribution in terms of the number of rainy days in the monsoon season is likely to change.

The results of the climate model runs, both global and regional, have to be viewed against the observed fact that the all-India summer monsoon mean rainfall has not show any statistical trend whatever over since at least 1875. Today, when even seasonal scale monsoon predictions are difficult to make and often go wrong, like in 2009, making climate scale monsoon predictions over the next 50 or 100 years remains a formidable challenge. There are only a few global models that can be trusted with this job and there is no single climate model currently available nationally or internationally that can be truly relied upon from all angles pertaining to the monsoon for purposes of policy making.

 

Agriculture: There have many investigations into the likely effects of climate change on Indian agriculture. However, many of them have considered only baseline shifts in temperature and rainfall, while it is well-known that Indian agriculture is extremely sensitive to the timing of wet and dry spells, heat and cold waves, etc. The incidence of crop pests and diseases is a major weather-dependent imponderable and it can very adversely impact the crop yields. Simplistic models often give rise to alarmist results and what are required are very robust models that would incorporate the diverse inputs that determine crop production.

 

Tropical cyclones: Tropical cyclones over the Bay of Bengal and the Arabian Sea are much fewer in number than those in the Pacific and Atlantic basins, but they have been responsible for comparatively much heavier losses of life and property in the countries of the south Asian region. One of the pre-conditions for the formation of a tropical cyclone over the ocean is that the sea surface temperature (SST) should be 26.5 °C or higher. Tropical storms therefore tend to form only over certain ocean basins of the world and in certain preferred seasons where and when there is a possibility of this condition being satisfied in the first place. The primary effect of global warming, logically speaking, would be to cause the climatological SST isotherm of 26.5 °C to spread out and so favour the formation of tropical cyclones over a larger oceanic area than at present. However, it should be remembered here that a warm ocean is just one of the many pre-conditions for the formation of a tropical cyclone, and not the only one. Further, it is not only the number of tropical storms that is important, but also the peak intensity that they reach, and the length and orientation of the tracks that they follow. Hence, statistical correlations between global warming and the frequency of occurrence of tropical storms cannot be derived or viewed in isolation without due regard to these other aspects.

 

The number of cyclonic storms over the north Indian Ocean constitutes a small statistical sample, the number of severe cyclonic storms is still smaller and the instances of storms developing into supercyclones are just a few. Further, the number of landfalling systems varies widely across different sectors of the Indian coastline making some states more cyclone-prone than others. Therefore, it is difficult to draw robust conclusions from a statistical analysis of historical data and derive periodicities or trends. Although there is some evidence of an increasing trend, it cannot be extrapolated simplistically into the future. A lot of modelling effort is required to be put in, including factors such as projections of the sea surface temperature so that more credible and realistic conclusions can be drawn.

 

Sea level rise: The sea level at a given place is influenced by several local factors such as coastal ocean temperature, salinity, wind, atmospheric pressure and ocean currents. The sea level is also affected by the changes in coastal geometry resulting from sedimentation, coastal erosion, storm surges and the action of waves. Tide gauge observations are available for some Indian coastal stations since the mid-nineteenth century and they have shown that mean sea level along the east coast of India is higher than that along the west coast. Sea level trends derived from historical tide gauge records are sensitive to the choice of stations and the data period analyzed but there is no evidence of a monotonic rising trend at any of them.

 

The prime advantage of satellite altimetry over tide gauge measurements is that satellite-derived sea level data are available across the oceans and not just on the coast. Satellite measurements have shown that over the Arabian Sea and the Bay of Bengal, sea level rise in recent years has been negligibly small and the sea level has in fact exhibited a fall in some parts.

 

Different sectors of the long Indian coastline have different physiographic and environmental characteristics. Problems such as erosion, flooding, subsidence, salinization and deterioration of local ecosystems like mangroves already prevail in the coastal regions. Anthropogenic factors also play a role in the deterioration of the environment of the coastal zone. There is, however, a growing tendency to attribute all sea level rise observed anywhere on the coast entirely to global warming, which needs to be curbed and a balanced view taken considering other possible reasons as well. 

 

Himalayan glaciers: The Himalayas, including the Karakoram range, constitute the largest glacier system in the world outside of Antarctica and Greenland. Scientific observations of Himalayan glaciers were started about a hundred years ago. The snout of the Gangotri glacier in Uttarakhand was mapped in detail way back in 1935 and it had shown signs of retreat even at that time. After the 1970s remote sensing satellites have made it possible to carry out glacier mass balance investigations on a large spatial scale. The retreat of glaciers has assumed great importance in recent years as it is being projected as an indicator of the current global warming. In the case of Himalayan glaciers, however, the issue is also of great practical concern as India’s three major river systems, Ganga, Yamuna and Brahmaputra have their origins in the Himalayas. 

 

Observational evidence indicates that the Himalayan glaciers have been exhibiting a continuous secular retreat since the earliest recording began in the mid-nineteenth century, and the retreat in the recent years in not unusual. Another interesting and important point is that not all of the Himalayan glaciers have been retreating. Making high quality and reliable measurements of glacier retreat at remote and inaccessible locations in the Himalayas is difficult but is greatly desirable. Otherwise one can very easily arrive at wrong and threatening conclusions. In fact many studies have shown that it is premature at the present time to say with certainty that the retreat of the Himalayas glaciers is attributable to the current global warming. Glaciers are known to be influenced by several geophysical features and local climate fluctuations and it is particularly difficult to correlate individual snout movements to large scale global warming.

 

Vector-borne diseases: The PRECIS model has been used recently for malaria incidence investigations and updated results under the A1B scenario have now become available for many parts of India. By the 2030s, compared to the 1980s, the Himalayan region and northeastern states of India are likely to be adversely affected by an increase in the transmission window, while the effect may be minimum over the Western Ghats and even beneficial over the east coast. Here again, such results have to be considered with due care and caution, since the incidence and spread of malaria is governed not just by temperature and humidity but by several other socioeconomic factors not related to climate such as urbanization, population migration, health infrastructure and intervention practices. For proper preparedness planning, there is a great need to construct comprehensive models which can envisage how these factors will evolve over time, with global warming being one of the inputs and not the only one.

 

Indian Monsoon Variability in the context of Global Warming debate

By: Dr. Madhav Khandekar

The Indian summer Monsoon is an important component of the earth's climate system and its inter-annual variability is governed by large-scale features like ENSO (El Nino-Southern Oscillation), Eurasian winter snow cover and extent, Quasi-biennial equatorial wind oscillation, Indian Ocean Dipole (IOD) etc. In this talk, the inter-annual variability of the summer Monsoon is analyzed in the context of the present debate on Global Warming and climate change.

Using a 200-year excellent dataset, it is shown here that the Indian Monsoon is a robust system and is NOT impacted at present by the recent warming of the earth's climate as claimed by the IPCC (Intergovernmental Panel on Climate Change) and its adherents. It is further documented that the Indian Monsoon exhibits a decadal variability with an approximate 30-year cycle of above/below normal rainfall.

 

A brief discussion of some of the past floods and droughts will be presented and implication of this analysis for predicting future droughts/floods will be discussed.


 


 
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