Climate Change – UGC NET Geography – Detailed Notes

Introduction

• Climate change encompasses both global warming and its effects on Earth’s weather patterns. There have been previous periods of climate change, but the current changes are noticeably faster and are not the result of natural causes.
• They are instead caused by the release of greenhouse gases, primarily carbon dioxide (CO2) and methane. The majority of these emissions are caused by the use of fossil fuels for energy production. Additional sources include certain agricultural practices, industrial processes, and forest loss. 
• Greenhouse gases are transparent to sunlight, allowing it to reach the Earth’s surface and heat it. When the Earth emits infrared radiation, the gases absorb it, trapping the heat near the Earth’s surface and contributing to global warming. 

Climate Change: Background

• Now, what is climate change? ‘Climate change’ means a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods. Increasing levels of fossil fuel burning and land use changes have emitted, and are continuing to emit, greenhouse gases (mainly carbon dioxide (CO2 ), methane, and nitrous oxide) into the earth’s atmosphere.
• This increasing level of emissions of greenhouse gases has caused a rise in the amount of heat from the sun trapped in the earth’s atmosphere, heat that would normally be radiated back into space. This has led to the greenhouse effect, resulting in climate change.
• The major characteristics of climate change are rise in average global temperature, ice cap melting, changes in precipitation, and increase in ocean temperature. The efforts needed to address the climate change problem include greenhouse gas emissions on the one hand and building of capacities to cope with the adverse impacts of climate change on various sectors of the society and economy on the other.
• Scientists who have been working on the subject for a long time point out that greenhouse gases (GHGs) such as carbon dioxide in the atmosphere trap the incoming heat from the sun and thereby leads to the increase in earth’s temperature which is often referred to as global warming. Besides carbon dioxide, other greenhouse gases are methane, nitrous oxide and water vapors.
• This climate change is likely to cause adverse change in weather patterns and extreme events such as cyclones, hurricanes, floods, and rise in sea level. How to reduce the emission of greenhouse gases and also to adapt to the changes in climate are the issues that confront the humanity.
• Why does carbon dioxide concentration in the atmosphere increase? Though human beings also emit carbon dioxide while they breathe, the most important source of carbon dioxide emission is burning of fossil fuels such as coal, oil, gas during the process of industrial production. As most of the industrial growth has taken place in the developed countries such as the USA, Europe and Japan over the last more than a century, it is they who have contributed most to the increase in carbon dioxide concentration in the atmosphere.
• It is the unsustainable consumption pattern of the rich developed countries that are responsible for much of the emission of carbon dioxide and other greenhouse gases by burning fossil fuels.
• While 25 per cent of world population lives in these rich industrialised countries, they emit more than 70 per cent of total global carbon dioxide emission.
• In per capita terms disparities in emission of carbon are also very large. Thus, while a citizen of USA on an average emits more than 5.5 tonnes carbon per year, an Indian citizen emits only 0.25 tonnes of carbon per year.
• It may be noted that though the developed countries emit more carbon dioxide and other greenhouse gases (GHGs) into the atmosphere, it is not only their local atmosphere that gets polluted, but the whole global atmosphere is adversely affected.
• The air and winds know no national boundaries; the emission of toxic gases into the air by one nation easily travels to the whole global atmosphere.
• Thus, there is climate change for India and other developing countries though it is the rich industrialised nations of the USA, European countries and Japan which have contributed most to the concentration of green house gases (GHGs) in the atmosphere.
• Similarly, the flow of sea water knows no national boundaries and therefore rise in sea level as a result of climate change will affect the people of coastal areas of many countries. Therefore, global cooperation and efforts are required to mitigate climate change.
• Climate is an average weather condition for a long period. A minimum of 25 years have to be considered for reliable statistical determination of the characteristics of a climate.
• Climate is never static; it is subject to fluctuations. The term, ‘climate change’, is defined as the climatic variations in historical time over the span of a few thousand years.
• The study of climate changes assumes importance in the context of the fact that all living beings have to adapt themselves to changes in climate.

Reconstruction of Past Climates

Morphological Indicators

• These include glacial features such as erratics; denudational features such as striations, cirques, arete, tarn, etc.; fluvial features such as river terraces; aeolian features such as dunes, inselbergs; periglacial features such as pluvial lakes.
• The glacial features indicate the former snowline whereas inselbergs indicate the presence of dry conditions in the historical past. Animal footprints and marine fossils found in deserts are valuable in analysing the past climate of a particular place. The fall in sea level during the past ages can be detected by the study of river terraces.

Lithogenic Indicators

• These include varves, evaporites, weathering processes, especially laterisation and resultant landforms, limestone deposits and coal deposits. Laterites are formed when wet and dry climates alternate. Redbeds prove the presence of tropical soil/climate in the past. Similarly, coal deposits indicate the past existence of forests in the area under study.
• The varves reveal the most detailed chronology for the past thousands of years. Varves are the annual layers of silt and sediment accumulated on the beds of lakes and ponds. During winter, only the fine suspended clay is deposited on the lake bottom even when the lake is frozen. At the onset of summer, fresh water and coarse sediments are introduced in the lakes.
• Therefore, no two successive layers of deposits have similar thickness. A comparison of varves in areas once under glaciers suggests the dates of ice removal. The varve records of Scandinavia reveal that the last glacial recession took place about 13,700 years ago.