Environmental Science

LESSON 37 THE CONSEQUENCES OF GLOBAL WARMING

The major impacts of climate change in India would be on the hydrology, water resources and agriculture of the country. A rise in sea level due to thermal expansion of sea water and melting of ice form high altitudes and latitudes is also expected. Climate variability and climate changes assume great importance for the Indian sub-continent because its economic performance and social progress are dependent on rainfall and climate change is likely to affect rainfall. India possesses a great variety and diversity of climate, varying form extremely hot to extremely cold, from extremely arid regions to extremely humid regions, from drought-prone areas to flood-prone areas. Climatic conditions govern to a great extent the operation of water resources in the country. The Himalayan rivers of India are ice-fed rivers and thus are very vulnerable to climate change. Rainfall is governed by the southwest and northeast monsoons. The distribution of Indian rainfall shows great temporal and spatial variations. About 80% of the total rainfall occurs during four monsoon months (June to September) and is not spread uniformly over the country, creating pockets of scarcity in some regions. Thus, large storages of water are required to meet the demand during the lean periods.

PRECIPITATION PATTERNS:

An increase in rainfall is expected near the Equator, and a decrease in rainfall in the subtropics. Decreased summer precipitation in North America, Europe and Africa combined with greater rates of evaporation due to rising temperatures, is predicted to lead to increased droughts. In other regions, greater rates of both evaporation and precipitation will likely cause an increase in very heavy rainfall that can lead to flooding.

DROUGHT:

One possible effect of global warming is an increase in droughts. A drought is a lack or insufficient amount of rain for an extended period of time. Drought causes water shortages, crop damage, streamflow reduction, and depletion of groundwater and soil moisture and it has serious negative impact on agriculture. The extremely unusual high temperatures in central Europe during the summer of 2003 led to the deaths of over 20,000 people. The term drought may refer to a meteorological drought (precipitation well below average), hydrological drought (low river flows and low water levels in rivers, lakes and groundwater), agricultural drought (low soil moisture), and environmental drought (a combination of the above). The socioeconomic impacts of droughts may arise from the interaction between natural conditions and human factors such as changes in land use, land cover, and the demand for and use of water. Excessive water withdrawals can exacerbate the impact of drought. The regions where droughts have occurred seem to be determined largely by changes in sea surface temperatures, especially in the tropics, through associated changes in the atmospheric circulation and precipitation. In the western USA, diminishing snow pack and subsequent reductions in soil moisture also appear to be factors. In Australia and Europe, direct links to global warming have been inferred through the extreme nature of high temperatures and heat waves accompanying recent droughts.

ICE MELT AND SEA LEVEL RISE:

Some of the most obvious impacts of global warming will be sea level rise that occurs mainly, because ocean water expands as it is heated. Melting of ice on glaciers and polar ice caps adds to the rise. According to the IPCC 4th Assessment report (2007) by 2100, the temperatures could increase by 1.1°C – 6.4°C and sea levels may rise by 18 to 59 cm. The scientific community projected that up to 20% of the world’s population living in river basins will be affected by flood hazards by the 2080s due to global warming (IPCC, 2007). Warming over the past few decades is reducing the extent of the 30.2 km long Gangotri glacier that feeds the perennial Ganges at a rate of about 17 metres per year. The rise in sea level due to glacial meltdown in the Himalayas is projected to range from 0.18 metres to 0.59 metres under various emissions scenarios by 2100. If global mean temperatures rise and stay on a sustained basis between 1 to 4 degree Celsius, the Greenland ice sheet could all but disappear. Higher sea surface temperatures, increased precipitation intensity, and longer periods of low flows will further intensify many forms of water pollution, which will have adverse impacts on ecosystems, human health, water system reliability, and operating costs.

AGRICULTURE:

In mid- to high latitude regions, moderate to medium local increases in temperature (1-3ºC), along with associated carbon dioxide (CO₂) increase and rainfall changes, can have small beneficial impacts on crop yields. In low-latitude regions, even moderate temperature increases (1-2°C) are likely to have negative yield impacts for major cereals. Increased frequency of heat stress, droughts and flooding events reduce crop yields and livestock productivity. Global agricultural production could be increased due to the doubling of CO₂ fertilization effect. Sometimes, rising of sea level will increase salinity, pushing back fresh water interface and affect the supply of fresh groundwater along the coastal areas. Some land areas will experience drying conditions while others will see increased precipitation, which will change the extent and types of species in forests. Based on meteorological analysis, upward trend in mean temperature, downward trend in relative humidity, annual rainfall and number of wet days in a year is expected  in India. Warming is also projected to reduce the agricultural output in India making small and marginal farmers more vulnerable. Agrawal (2008) indicated that the agricultural productivity will decline upto 25 % which could be as much as 50 % in rainfed agriculture.

ACIDIFICATION OF OCEAN:

The ocean takes up roughly one quarter of human emissions to the atmosphere of carbon dioxide from fossil fuel burning and deforestation. Additional carbon dioxide uptake causes direct changes in seawater acid-base and inorganic carbon chemistry in a process termed ocean acidification. Acidification is independent of warming of the atmosphere but the two are linked through the underlying cause of elevated atmospheric carbon dioxide.  Ocean acidification affects the process of calcification by which living things create shells and skeletons, with substantial negative consequences for coral reefs, mollusks, and some plankton species important to ocean food chains.

OZONE LAYER DEPLETION:

Ozone in the lower atmosphere is a dangerous pollutant that adds to the greenhouse effect, damages plants, and damages lung tissue. However, ozone is essential in the upper atmosphere for reflecting excess rays from the sun. It’s ironic that at ground level ozone is a health hazard, but in the stratosphere we couldn’t survive without it. In the past few decades, chemical reactions involving chlorine and bromine are destroying ozone in the southern polar region. These compounds rise into the atmosphere and are struck by high-energy light waves from the sun, creating reactive compounds that destroy ozone. This depleted region is known as the ozone hole. Scientists believe this is due to the release of man-made chemicals like CFCs.

Oceans naturally absorb carbon dioxide from the atmosphere. When there are increased levels of carbon dioxide in the atmosphere, oceans increase absorption, resulting in ocean acidification. The mixture of ocean water and carbon dioxide forms carbonic acid. Carbonic acid reacts with carbonate ions that are also found in seawater, which are a vital component to the structure of corals and the shells of marine organisms, such as calcifying phytoplankton, that form the first tier of the ocean food web. So in other words, elevated levels of carbon dioxide in the atmosphere leads to less of the building blocks that are needed to form the calcium carbonate skeletons of corals and other organisms that require calcium carbonate to make their shells.

Ocean acidification, warmer ocean water and more saline estuaries are expected to have several impacts on coastal and ocean resources.

• Potential marine food web breakdowns

• Coral, calcifying phytoplankton and zooplankton growth will be inhibited or slowed

• Habitat loss with the loss of coral reefs

• And Aquatic plants and animals that cannot tolerate increased salinity levels are lost.

SOCIAL CHANGES:

According to the World Health Organization’s (WHO , an estimated  150,000 deaths occurred in 2000 due to climate change. An unprecedented heat wave in 2003 left 14,800 people dead in France alone, representing a 60 percent increase in expected mortality. Much of North America experienced a severe heat wave in July 2006, which contributed to the deaths of at least 225 people. Five hundred people died in the European heat wave of July 15–22, 2007. One can readily see that global warming is already happening and is an important threat to human life.

In India, average food consumption at present is 550 g per capita per day, whereas the corresponding figures in China and USA are 980 and 2850 g respectively. Present annual requirement based on present consumption level (550 g) for the country is about 210 million tonnes (mt), which is almost equal to the current production. While the area under food-grain, fell from 126.67 million hectare (mha) to 123.06 mha during the period 1980–81 to 1999–2000, production registered an increase from 129.59 to 209 mt during that period. Food grain production was impressive in 1999–2000, which is more than four times the production of 50.82 mt in 1950–51. However, the country faces major challenges to increase its food production to the tune of 300 mt by 2020 in order to feed its ever-growing population, which is likely to reach 1.30 billion by the year 2020. To meet the demand for food from this increased population, the country’s farmers need to produce 50% more grain by 2020. It is feared that the fast increasing demand for food in the next two or three decades could be quite grim particularly in view of the serious problem of soil degradation and climate change.