Issues with Climate Change and Global Warming
Temperature, precipitation, sunshine, cloudiness, pressure, wind velocity, wind direction and humidity are important elements of weather. These elements are variable in both at temporal and spatial scale. The scale of temporal variation varies from very few hours to thousands of years. The inter-annual variations in the climatic phenomena are in most parts of the earth surfaces and experienced almost every year. No two years have the same recording of the elements of weather at a place. However a successive group of years may have similarity in the climatic conditions which may be termed as cool or warm periods and wet or dry periods. Such period of time which is larger than one year but upto 30 years is termed as climatic fluctuation. The deviation from the normal course of climatic conditions exceeding the periods of 30 years is termed as climatic change.
Evidence of Climatic Variations
The climatic conditions have been quite common during the climatic history of the earth. But the reconstruction of the past climates is a very difficult task as the weather data recorded by the instruments is available since 1861 only. The observation of upper air circulation began as late as WW II. Hence we need to rely upon the non-instrumental sensors to reconstruct the past climates. There are various types of evidences available for assessing the climates of the past longer than a couple of centuries.
The records of human history provide definite information on climatic events such as droughts, floods, storms cyclone and other climatic extremes. The records of large-scale migration, exodus, settlement, habitation and desertion in a region provide sufficient indications to corroborate these climatic events. The nature of crops cultivated dietary habits and staple food of the people also indicate towards the climatic conditions prevailing at the given time in the region.
The remains of grazing animals and their predators provide information about the nature of vegetation. The natural vegetation is so much influenced by the climatic conditions that it is taken as index of climate. The analysis of pollens in cores taken from bog and lake bottom also provides information about past climates. The changing character and type of pollens in different varves indicate the changing type of natural vegetation and climatic conditions. Analysis of cores may clue to the climatic records for thousands of years. In Scandinavia varves taken from lakes and bogs has provided information on climates dating back to 13700 years.
Evidences of past glaciations are foremost climatic sensors. The study of moraines in the glaciated topography clues about past climates. Location and arrangements of moraines provides insight about glaciations history and climatic changes. The study of ancient beaches, sediments mostly under sea level, provides information about ice age as well. The fossils of plants and animals in the layers of sedimentary rocks also provide information on past climates. Some of the fossils are found at the places where dramatic climatic changes have taken place.
Climate changes in the past
The evidences of climatic change become blurt as we go in the past. Some investigations have suggested that 5 major ice ages have occurred prior to 600 million years ago.
The term ice age refers to the cool periods prevailing on the earth’s surface for a period of few decades to many thousands of years. A French Swiss biologist Louis Agassiz while studying the glaciers of alps in 1836 coined it. It is used to describe the climates which permitted glaciations. By early 20th century it was established that a large part of Eurasia and North America had experienced glaciations in the past. There are also evidences of glaciations in Sahara and India as well. The evidences of hippopotamus in England and coal beds in Antarctica also indicate towards climate change in the past.
The estimated period of glaciations and intermittent warm periods are mentioned as under:
- 600 million years before present – glaciations
- 300 million years before present – glaciations
- 65 million years before present – warm period ; no polar ice
- 55 million years before present – glaciations
- 45 million years before present – appearance of Antarctica ice sheet.
- 2 million years before present – Pleistocene ice age; continental glaciers appeared in northern hemisphere
- 18000 to 22000 years ago -Last major glaciations; glaciations in north America and Scandinavia where ice covered about 90% of the maximum extension ever over these continents.
- 14000 years ago
– warming (retreat of ice)began
- 1850 AD to present – average temperature rising by 0.6 degree c; 1980s was warmest decade 1998 was warmest year of 20th century
The global warming is a major cause of concern in the world today. It has attracted the attention of the world community whether belonging to the developed world or the developing one. During the last two decades or so the scientists, academicians, political ad state establishments, social and political activists and various voluntary agencies have show a very keen interest in the trends and impacts to rising temperature of the globe on various spheres.
Trends in global warming
The increasing concentration of Green House Gases in the atmosphere has been responsible for increase in the global average surface temperature. The temperature has been recorded to be increasing since 1861, the year since which instrumentally recorded data is available. Inter governmental panel on climatic change (IPCC) has provided the authentic estimates of global warming.
According to the earlier estimate te average temperature of the earth’s surface would increase between 0.6 degree C and 1.5 degree C during 1990 and 2020. It had also been estimated that by 2100, the average temperature of earth’s surface would increase by 3 to 5 degree C. But this is the likely only if the GHG concentration increases at the present rate.
The evidence of global warming is also provided by widespread retreat of mountain glaciers in non-polar regions during the 20th century. The satellite imageries reveal that since 1960s the snow cover as decreased by about 10 percent. There has also been reported reduction in duration of lake and river ice covers in mid and high latitudes by about 2weeks in the 20th century.
Other climatic events related to global warming 0.2 to 0.3 percent increase in precipitation in tropics during 20th century. There has been 2 to 4 percent increase in the frequency of heavy precipitation events in mid and high latitudes since 1950s, 2 percent increase in cloudiness in mid and high latitudes in northern hemisphere during the 20th century and increase in the frequency of ENSO since 1970s as compared to the previous 100 years.
The situation is likely to worsen in 21st century. According to the Met. Office UK in the business as usual situation, the average temperature of the earth’s surface shall be higher by 3.2 degree C. in 2080s than 1990. The temperature of the surgace air is estimated to increase by 1.4 to 5.8 degree C. over next 100 years.
Impacts of global warming
Global warming being experienced currently is likely to influence various aspects of earths systems.
- Impacts on agriculture
The magnitude of the effect of global warming would also vary over different agro-ecological regions of the world. The increase in the precipitation is likely to increase the soil moisture availability. There is also likely to be longer cropping season in the higher latitudes. But there is possibility of soil moisture deficiency in the middle latitudes. This may affect the agricultural productivity in mid latitude granary in the northern hemisphere. Impacts of global warming on the other hand, increase in the level of carbon dioxide is also likely to have the fertilizing effect on the bio-mass. Despite this the yield of most crops is likely to decline in large parts of United States, European Economic Community, Northern Europe, Russia, Australia and Japan.
- Impacts of sea level rise on coastal areas
Another impact of the global warming is rise in the sea level on account of thermal expansion of water and melting of ice cover. The global average sea level has been estimated to increase by 0.1 to 0.2 m during 20th century. The global mean sea level rise between 1990 and 2100 has been estimated to be 0.09 to 0.88m. This is likely to inundate the coastal areas in many parts of the world. An average increase in the sea level by 1 m is likely to submerge about 3 percent of the land and much more 90 percent of ice on the earth, shall be the main source of melted water. The most affected countries in terms of submergence are likely to be Bangladesh, Thailand, Egypt, china and Indonesia.
- Impacts on forestry
Natural vegetation is very closely associated with the climatic systems. Therefore, changes in the climate would alter the configuration and productivity of ecosystems. These changes in turn would significantly affect the traditional livelihood, biodiversity, soil and water resources, and thereby the agticulrural productivity. A study conducted by Ravindernath and Sukumar (1998) concludes that greenhouse and subsequent increase in temperature and rainfall could result in increased productivity, migration of forest types to higher elevations and transformation of drier forests to moisture forests. On the other hand increase in sulfate aerosols may lead to moderate increase in temperature and decrease in precipitation in central and northern India could have adverse effect on forests.
- Other impacts
Other impacts of global warming include damage of the biomes and ecosystems, spatial expansion of tropical diseases such as malaria and increase in illness and mortality in the summer and increase in the energy consumption in mid latitudes for cooling. The boreal forests, which provide a large amount wood Is likely to experience decline in its productivity as result of destruction of the ecosystems. The temperate grassland providing pastures for sustaining the animal husbandry in mid latitude are also likely to be affected and the productivity of these pastures declines in the wake of global warming.
Team Aspirant Forum