Q. 1. Describe the broad climatic groups framed by Koeppen.
Ans. Koeppen’s Classification.
The aims and objectives of Koeppen climatic classification were very clear. He opined that, people such as geographers, biologists, or agriculturists, who need to understand and use the climatic environment for their own purposes, should have the facts of climate presented realistically. At the same time he also recognised the merits of the genetic type of climatic classification.
Koeppen classified world climates in six great climatic groups, out of which, five (A, C, D, E, F) are based on temperature criteria, and the sixth (B) is the dry group based on precipitation.
Simplified Version of Koeppen’s Climatic Classification System
Climatic Groups Based on Temperature Criteria
(1) Tropical Humid (A) Climate. The tropical humid (A) climate stretches along the equator, in the irregular belt of 20o to 40o latitude in both the hemispheres. The temperature and rainfall are high throughout the year. In the coastal region the average temperature of the coldest month is above 18o C.
(i) Tropical Wet Climate (Ar). The core of the 'A' climatic region is constituted by wet sub-type, the tropical wet climate (Ar). This climate extends approximately 5o to 10o on either side of the equator. Along eastern margins of continents, this type of climate is under the influence of inter-tropical convergence zone and the sub-tropical jet-stream. It is also known as tropical rain forest.
Closer inspection of tropical wet climate reveals that it widely extends (15o to 20oN and S) on the eastern margins of continents because trade winds blow on shore from northeast and southeast.
(ii) Tropical Wet and Dry Climate (Aw). The tropical wet and dry climate (Aw) exhibit winter dry season. It is dominated by dry trade winds. In this region average precipitation is less than the one in tropical wet climate. This type of climate is called savanna climate because tall grasses that grow between trees and thorny bushes, dominate the vegetation cover.
(2) Sub-Tropical (C) Climates: Sub-tropical climates are found between tropical and temperate climatic zones. In this type of climate, the temperatures are generally, above 18oC for nearly 8 months. Winters are mild and short. The coastal areas have rainfall throughout the year while continental areas receive less rainfall. On the basis of seasonal distribution of precipitation, subtropical climates have two sub-types: sub-tropical humid (Cfw) and sub-tropical dry summer (Cs).
(i) Sub-tropical humid climate (Cw): The subtropical humid climate is found on the eastern sides of continents. In this type, the rainfall is throughout the year. During summer, it is under the influence of subtropical anticyclone and in winter under temperate cyclones. The summer months receive more rainfall than winter.
(ii) Sub-tropical dry climate (Cs): Sub-tropical dry summer climate is characterised by moderate to scanty rainfall. Rainfall occurs in winter while summers are dry. This type of climate is found in the interior of 'C' climate region along the tropical margin of mid latitudes.
(3) Temperate (D) Climates. The micro thermal (D) climates receive relatively small amount of heat. It is found in the vast landmasses of middle latitudes (40o and 65o). This climatic band of severe winters is found between sub-tropical and boreal types of climate. The two sub-types of temperate climates are temperate marine (Do) and temperate continental (Dc). They are primarily demarcated on the basis of summer temperatures.
(i) Temperate Marine Climate (Do). Temperate marine climate has mild winters and fairly warm summers. Throughout the year, average temperature is above 0oC. The rainfall is experienced throughout the year. This type of climate is found on the western sides of continents in temperate zone.
(ii) Temperate Continental Climate (Dc): Temperate continental climate is found in the interiors of the continents in middle latitudes. The impact of land is visible as it is characterised by harsh winters and cool summers. The extreme cooling of the ground is associated with anticyclone. Annual precipitation is low, though it takes place throughout the year. This type of climate is found in north-eastern Asia, eastern Canada and Eurasia.
(4) Boreal (E) Climates. Boreal climate is found in the higher middle latitudes. In this climate, summers are short and cool, winters are long and cold with a very short frost-free season. Annual temperature ranges between 0o and 10o C. Annual precipitation is meager and most of it occurs during summers. This type of climate is noticed in the coniferous forest of the world.
(5) Polar (F) Climates. Polar climates are found in the high latitudes and higher reaches of the Himalayas and the Alps. These climates are confined to the northern hemisphere only. The average temperature does not exceed 10oC in any month. There is no summer season. On the basis of temperature the polar climates are classified into two types:
(i) tundra (Ft); and (ii) ice cap (Fi).
(i) Tundra Climates (Ft): The Tundra climate on land is found only in the northern hemisphere where it occupies the coastal fringes of the Arctic Ocean, the ice-free shores of the northern Iceland, southern Greenland and higher reaches of the Himalayas and the Alps. This climate is characterised by extreme cold in which the average temperature of the warmest month does not normally rise above 0oC, but never above 10oC. It is associated with permanent frost formation leading to frozen sub-soil. During the summer, precipitation occurs in the form of snow and rain.
(ii) Icecap (Fi): Icecap climate has average temperature below freezing point. It is associated with the phenomena of permanent ice and snow. The winter and summer are windy and chilly and precipitation is very meagre. This type of climate is confined to icecaps of Greenland and Antarctica.
(6) Climatic Group Based on Precipitation Criteria
Dry (B) Climates: The dry climates are found on the poleward margins of 'A' group climates on the western sides of the continents. The most important feature of a dry climate is the higher rate of moisture-loss through evaporation and evapo-transpiration in relation to the annual receipt of water gain from precipitation. This climate is characterised by dry weather with a high range of temperature – 25o to 30o C.
Dry B1 climates are associated with subsiding air of sub-tropical high pressure zone which, results in intrusion of arid climate into continents of both north and south hemispheres. The extreme seasonal temperatures cause large annual range of temperature. The average annual precipitation is meagre (nearly 0 to 50 cm) and is highly variable.
On the basis of annual average range of precipitation, dry climates are sub-divided into desert (BW) and semi-arid (BS) type of climate. The capital letters 'S' and 'W' indicate the degree of aridity in dry (B) climates, with 'S' and 'W' designating semi arid and fully arid conditions respectively. The boundaries of these two sub-climates are set at one half of the annual rainfall separating dry (arid) from the semiarid type.
(i) Desert type (Bw): Desert or arid type of climate has driest climatic variety in sub-tropical belt between 20o to 30o north and south latitudes. This type of climate is found in coastal deserts of Peru and Chile in South America, Kalahari deserts of coastal Angola, south-west Africa, Great Australian desert, Sahara and Arabian deserts. Thar desert of Pakistan and India and deserts of northern Mexico. In these regions stability of air mass leads to extreme dryness with no rainy days. The influence of cold ocean currents is also there. These areas receive lowest annual rainfall in the world despite their location adjacent to the oceans.
This type of climate is associated with xerophytic (thorny / spiny) type of vegetation.
(ii) Semi-desert (Bs). The semi arid or steppe type of climate borders 'A' and 'C' type of climate and has an annual rainfall range of 30 to 60 cm. These areas lie in the heart of the grasslands of western North America and Eurasia. That is why they are called steppe type of climate. The lands of this climatic type are away from the oceanic influence. It is found in both north and south tropical deserts from Morocco to Tunisia and from Dakar in Senegal to Ethopia deserts of Afghanistan, large strip of land adjoining Thar Desert and rain shadow area of peninsular India.
Q. 2. Describe the Global Warming in details.
Ans. Global Warming. Global warming means the increase in the average temperature of the earth.
Processes of Heating the Earth The atoms and molecules of atmospheric gases cause absorption and back radiation of sun light, by the green house gases (discussed in later part of this chapter) especially water, carbon dioxide, and methane. The concentration of water in the atmosphere is controlled by evaporation from oceans. Carbon dioxide is introduced in the atmosphere by volcanism. Equivalent amount of carbon dioxide is removed by precipitation as calcium carbonate in oceans. Methane, which is twenty times more effective than carbon dioxide, is produced by metabolisation of bacteria in wood / grass eating animals.
The methane rapidly gets oxidised into carbon dioxide.
Effects of Human activities Human activities add methane and carbon dioxide to the atmosphere by burning fossil fuels and by various agricultural activities. The carbon dioxide contents of atmosphere play a dominant role in causing worldwide climatic change. The gas is transparent to incoming solar radiation, but absorbs outgoing long-wave terrestrial radiation. The absorbed terrestrial radiation is radiated back to the earth's surface. Thus, it is clear that any appreciable change in carbon dioxide content would bring about changes in the temperature in lower layers of the atmosphere.
Rapid industrialisation and technological changes, revolution in agriculture and transport sectors has resulted in large supplies of carbon dioxide gas, methane and chlorofluorocarbon gases to the atmosphere. Some of these gases are consumed by vegetation and part of it is dissolved in ocean. However, about 50 per cent is left over in the atmosphere.
Examples : (i) During past 100 years the concentration of methane has more than doubled (from 7.0 × 10–7 to 15.5 × 10–7).
(ii) Carbon dioxide has increased by 20 per cent (from 2.90 ×10–4 to 3.49 ×10–4).
(iii) In 1880-1890 the carbon dioxide content was about 290 parts per million (ppm). It rose to about 315 ppm in 1980, 340 ppm in 1990 and 400 ppm in 2000.
(iv) This means that proportion of carbon dioxide had increased to 9 per cent by 1950 and nearly 17 per cent by 1990. The rate of increase has become still greater during last one decade.
Effects of industrialisation Of the many climatic parameters, temperature is the most affected one due to urbanisation and industrialisation. The thermal characteristics of urban areas are in marked contrast to those of surrounding countryside. The analysis of temperature data for last fifty years reveals that there is an increase of 0.7oC in winter and 1.4oC in summer in India.
Effects of Agriculture Man is considered an engine of climatic change. In support of this, rice farmers, coal miners, dairy farmers and shifting agriculturists contribute their mite in global warming. According to some estimates, rice cultivation in the world is responsible for 20 per cent methane being added to atmosphere, and the coal mining accounts for 6 per cent of methane. The deforestation is responsible for 20 per cent of the carbon dioxide gas being added to the atmosphere. Similarly, industrialisation is adding 25 per cent of chlorofluorocarbon to the aerosol of the atmosphere. Consequently, global temperature increase is by about 1.5oC.
Rise in Sea-level Today, there is much concern that continuing addition of carbon dioxide and methane gases to the atmosphere will increase atmospheric temperature to an extent that it will cause ice to melt in the Arctic Ocean and in Antarctica. As a result, sea level will rise causing drowning of coastal lowlands and islands, altering rainfall and evaporation patterns, creating new plant diseases and pest problems and enlarging the ozone hole.
With a view to get a dependable picture of climatic changes in the past, ice-coring programmes have been undertaken in several countries particularly in Antarctica and Greenland Ice caps to analyse the trapped gases during the last 1,00,000 years.The results have been fascinating and offer glimpses of the earth’s recent history going beyond the phenomena of global warming. During last 10,000 years of the earth’s history, climate regime has been exceptionally stable compared to earlier history. Study of oxygen isotope records in Greenland ice core suggests that cooling trend in the northern hemisphere started from 1725 to 1920.
These were associated with emissions of volcanic dust at a regular interval of two to three decades but after 1945 there has been increase in temperature globally leading to warming without any major volcanic eruption and increase in level of carbon dioxide concentration in the atmosphere. Future scientists predict that by 2020, temperature all over the world, would be higher than ever during the last 1,000 years. As such, it is evident that increasing carbon dioxide content would lead to rise in global temperature.