What is Global Warming? Greenhouse Effect, Causes and Impact of Global Warming


What is Global Warming? Greenhouse Effect, Causes and Impact of Global Warming

Global Warming -Introduction

Global warming refers to the gradual rise in atmospheric and ground surface air temperatures and consequent changes in global radiation balance, caused mainly by anthropogenic processes leading to climate changes at different levels.

It is often used interchangeably with climate change but is to be differentiated from it. Climate change is about all types of climatic variability over the planet. Whereas, global warming is with respect to global surface temperature only. 

Global warming results from a rise in the proportion of atmospheric greenhouse gases than their normal level. The rise of greenhouse gas levels has been attributed to industrialization, urbanisation and pollution caused by vehicular, industrial, domestic and agricultural emissions. The main component gases of greenhouse gas emissions are - Carbon dioxide, methane, chlorofluorocarbons, nitrous oxide and ozone.

The processes of global warming have led to the effects of climate change, the evidence of which has been scientifically corroborated by the International Panel on Climate Change (IPCC), formed under the United Nations Framework Convention on Climate Change (UNFCCC) and constituted by the United Nations Environment Programme (UNEP) and World Meteorological Organisation.

Evidence of Global Warming- 

  • Increase in air temperature: It has been estimated that the overall increase in the air temperature in the 20th century has been about 0.5 to 0.7° C. The 1990s saw seven out of the warmest years of the last century. The global circulation models have shown a rise of 0.4 to 0.8° C in the 20th century. The increase in the frequency of EL Nino events, hurricanes and cyclones between the 1970s to 2012 also denotes climate changes due to the warming of the earth’s surface and its atmosphere. IPCC report has shown that the concentration of atmospheric carbon dioxide has increased. 
  • Melting of Mountain and Continental Glaciers: Many reports have suggested that Himalayan Glaciers have receded. Similarly, there have been reports of the retreat of glaciers in the Alps, Andes, Russian Caucasus, Chinese Tien Shan mountains, and Southern Alps of New Zealand. Mt. Kenya has lost its most extensive glaciers in the past century. The glaciers of Greenland too have been detaching and receding at a fast pace.
  • Warming of Ocean Water and Melting of Ice Sheets and Ice Bergs in the Antarctic and Arctic Sea: Due to the rise of ocean water temperature in the Indian Ocean, during 1997-98 catastrophic coral bleaching was observed causing the death of almost 7% of the corals near Andaman and Nicobar and Lakshadweep Islands. Analysis suggests that average sea temperature has risen by 0.6% C during the later half of the 20th century. 


A greenhouse is a glass house that helps in the artificial cultivation of plants by providing a conducive environment for their growth. GHE was given its name by a French Physicist named Joseph Fourier in 1827 who compared the earth's atmosphere to a closed glass vessel and observed that air around the earth filters sunlight exactly like a glass roof. 

Greenhouse Effect: 

Present climate change is caused by human activities which alter the composition of the global atmosphere and disrupt the planet’s heat budget.

Most of the solar radiation which reaches the Earth is of relatively short wavelength - that is in the infrared and visible wavelength. Whereas, the energy radiated back by the warmed earth is relatively long-wave radiation. 

Certain gases in the Earth’s atmosphere are strong absorbers of the longwave radiation emitted by the warmed surface of the Earth. As these gases become warm by absorbing this radiation, they re-emit radiation, some of which goes back to the Earth’s surface. This makes Earth warmer than it otherwise would be. Thus, these gases trap the heat. This process is called as Greenhouse Effect. 

Without the natural greenhouse effect, the average temperature at the earth’s surface would be below water's freezing point, i.e. -18° C. 

Greenhouse Gases: 

Carbon dioxide and certain other trace gases including methane, nitrous oxide, chlorofluorocarbons and Ozone are accumulating in the atmosphere as a result of human activities. All of these are greenhouse gases that absorb radiated heat from the sun, thereby increasing the temperature of the atmosphere. Additional, though minor, greenhouse gases include carbon tetrachloride, methyl chloroform, chlorodifluoromethane, sulphur hexafluoride, fluoroform and perfluoroethane.

The greenhouse Effect is a natural phenomenon and ensures moderate temperature for life to exist over the planet.

Post-Industrial revolution, Greenhouse gas emissions have increased, in turn increasing the greenhouse effect in the atmosphere. This has led to the trapping of excess heat in the earth-atmosphere system and is the major driver of present human-induced climate change. 

Major Anthropogenic Sources of Greenhouse Gas - 

Greenhouse gas that is responsible for the greenhouse effect in the atmosphere includes carbon dioxide (largest volume), methane, chlorofluorocarbons (highest trapping capacity), oxides of nitrogen, sulphur hexafluoride and water vapours.

Greenhouse gas found in the atmosphere covers the earth like a blanket. Although high concentrations of these gases are harmful to the environment.

The important greenhouse gases and their anthropogenic sources are given below.

  • Carbon dioxide - Fossil-fuel burning, Firewood burning, Deforestation and land use change, Cement manufacture.
  • Nitrogen oxides - Burning of fossil fuels; Application of fertilizers in agriculture; Burning of wood and crop residues.
  • Methane - Rice paddy fields; Cattle and livestock rearing; Burning of wood and fossil fuels; Landfill sites.
  • Tropospheric Ozone - Burning of fossil fuels.
  • CFCs and other Halocarbons - Refrigeration and air conditioning compounds; foams, aerosol propellants.

Because of excessive deforestation, use of fossil fuel, automobile exhaust and various other industrial activities, the level of carbon dioxide especially has significantly increased which has resulted in increased temperature of the earth's surface. In 1957 it was recorded as 311 ppm (parts per million) and in 2005 it was recorded as 379 ppm. 

Global warming has occurred in two phases from 1910 to 1940 by about 0.350° C and more strongly from 1970 onwards to the present by about 0.55° C, taking the global temperature to about 14.4° C. If the increased concentration of carbon dioxide and other greenhouse gas continues this way by the end of the 21st century, the earth will become altogether an inhabitable planet. 

Causes of Global Warming - 

Release of greenhouse gases in the atmosphere is the cause of global warming. Man-made causes do more damage than natural causes.

Following are the major causes of global warming: 

  • Deforestation - Deforestation leads to global warming by releasing carbon stored in the trees. If the trees burn, the carbon is released immediately. If the trees are cut and removed, half the carbon remains in the form of branches, twigs, etc. When they decompose, the carbon is slowly released. 
  • Shrinking carbon sinks and changes in land use - Forests, peatlands, mangrove forests, seagrass meadows, kelp forests etc. and other land and water-based natural ecosystems act as carbon sinks. The process of absorption of carbon in a sink for long-term storage is called Carbon Sequestration. For example, the process of photosynthesis by forests is biological C- Sequestration. The natural ecosystems which have long acted as carbon sinks are being lost or degraded at a fast rate. For example - almost 20% of Amazon rainforests disappeared in the last 50 years. As per World Meteorological Organization (WMO), some major ecosystems are being lost at a rate of up to 3% per annum. When degraded, these ecosystems emit the carbon they have stored for centuries and thus become sources of Greenhouse gases. 
  • Role of Automobiles - The automobile is one of the most desired items of consumption today and the demand seems insatiable. From about 50 million in 1950, the numbers increased to more than 1 billion in 2010. The US alone has 25% of all cars in the world. China is now the second-largest car market in the world. The automobile contributes to a range of environmental problems by increasing air and noise pollution, accelerating global warming.
  • Chlorofluorocarbons - Chlorofluorocarbons are a group of organic compounds with contain carbon, chlorine and fluorine. In 1928, Thomas Midgley invented a compound called Freon. It was used as a refrigerant. Freons are Chlorofluorocarbons or CFCs. These compounds do not occur naturally. These were manufactured by laboratory synthesis. They were used as refrigerants, propellants in aerosols, metal degreasers, dry cleaning solvents etc. In 1974, it was found that CFCs reach the high stratosphere and damage the ozone layer. CFCs are important greenhouse gases. CFCs cause global warming. Therefore, they were banned globally.

  • Forest fires - Intentional or accidental human-induced fires do cause global warming. Such fires emit a large amount of carbon-containing smoke which increases the earth’s temperature. These fires have become a major problem in large forests, especially in countries like Canada and the US. In a number of developing countries, fires continue to be used for land- clearing with adverse consequences.
  • Volcanic Eruptions - An active volcano erupts many harmful gases like carbon dioxide, sulphur dioxide, oxides of nitrogen etc into the atmosphere and affects the climate. Large volcanic eruptions inject light-reflecting particles into the upper atmosphere. 

Inter-governmental Panel on Climate Change (IPCC) Special Report 1.5° C observes that ‘human activities have caused approximately 1 degree C of global warming above pre-industrial levels’. 

What is Global Warming? Greenhouse Effect, Causes and Impact of Global Warming

Impact of Global Warming - 

There will be changes in climatic conditions at local, regional and global levels with environmental, social, economic and political effects. The main ecological effects will be as follows: 

1. Natural disasters 

There were an unprecedented number of natural disasters during the 1990s and that trend continues in the twenty-first century. Direct and insured losses from weather-related disasters have increased substantially in recent decades, both globally and regionally. 

2. Ocean and coasts

The ocean has become warmer and more acidic and sea levels are rising. The melting of polar ice caps is adding to the problem. Small islands like those of the Maldives, South Pacific, and Sundarbans are threatened. If sea levels continue to rise, coastal areas will be flooded in places like the Netherlands, Egypt, Bangladesh, and Indonesia, necessitating the evacuation of large populations.

Coral reefs are already dying all over the world due to human activities. A warmer and more acidic ocean will accelerate this process. Corals are home to 9 million different kinds of marine plants and animals. Their death will have a devastating effect on marine life and fisheries. 

3. Melting of glaciers, ice caps, and permafrost 

Glaciers continue to shrink worldwide, Permafrost is warming and thawing in high-latitude regions and in high-elevation regions. The most dramatic evidence of this change is the melting of the Arctic.

4. Water, agriculture, and food  

In many regions, changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality. Negative impacts of climate change on crop yields have been more common than positive impacts. 

Extreme floods and droughts are likely to have serious effects on water resources, agriculture, and food security: 

  • Loss of topsoil, erosion of soil, and desertification 
  • Overflow of sewage systems and resulting water pollution and epidemics 
  • Amount and location of fresh water affected by changing rainfall, melting ice, and more evaporation ( For example, if the Himalayan glaciers are gone, there will be no water for 500 million people.) 
  • Warmer water attracts more organisms and gets contaminated 
  • Sea-level rise bringing salt water into coastal marshes and aquifers 

5. Animals, Plant species, 

Many terrestrial, freshwater, and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances, and species interaction in response to climate change.

Thousands of animal and plant species will go extinct, unable to adjust quickly enough to the new conditions. Polar species may be the first to go, followed by those in the coastal zones everywhere. 

Warming will increase photosynthesis activity leading to faster growth of plants and trees. Initially, the yields will be more, but too much heat will kill the crops.

6. Human Health

The relationships between human health and climate work at the systemic level, and both are complex and inseparable. Some forms of impact are evident as, for example, the 2003 heat wave in France resulted in around 15000 deaths. The ranges of mosquitoes and other disease carriers are likely to expand into the newly warm areas and spread malaria, dengue fever, leishmaniasis and yellow fever.

Extreme weather will increase human migration. There will be many millions more environmental refugees. People living on the coasts will suffer extensive damage due to sea-level rise and cyclones.  

7. Increase in hunger all over the world - 

The world is going to face food shortage. Increasing drought and desertification will spread.

Control of Global Warming - 

Global warming control needs to decrease greenhouse gas emissions. If we can decrease the emission of these gases, then, we can control global warming to a great extent. GHG emissions can be decreased by planting trees, curbing deforestation, use of air pollution control strategies etc. 

Following are some of the measures to control global warming : 

  • Planting more trees can decrease the amount of carbon dioxide in the atmosphere.
  • Air pollution due to vehicles and power plants is a major source of greenhouse gas emissions. Air pollution control devices can decrease global warming greatly.
  • Methane gas can be decreased in our atmosphere by using it as fuel in biogas generators.
  • The use of Hybrid gas-electric engines can reduce global warming pollution by one-third or more.
  • The use of renewable sources of energy can cut down the fossil fuel combustion processes. California has attempted to get 20% of its electricity from renewable sources b 2017.
  • Strict laws and agreements should be framed to stop the emission of greenhouse gases as far as possible. This will help to prevent global warming. 

International Efforts to Reduce Greenhouse Gas Emissions - 

At least 174 nations have now signed the U.N. Framework Convention on Climate Change (UNFCCC) developed at the 1992 Earth Summit. The international community recognises that the Kyoto Protocol is the only first step in addressing climate change. 

Frequently Asked Questions - 

Question - What is Global Warming?

Answer - Greenhouse gases strongly absorb infrared radiation. They block a large portion of the earth’s emitted radiation and do not allow it to escape. This increases the temperature of the earth.

Scientists predict that the earth’s average temperature will increase by many degrees in the next century. This will raise the sea level. This will cause important changes in weather patterns in the whole world. This is called global warming.

Question - What is Greenhouse?

Answer - A greenhouse is a small house made of glass that is used to grow plants. Glass walls in a greenhouse decrease airflow. This increases the temperature of the greenhouse. Plants grow in this warm temperature inside a greenhouse. The earth’s atmosphere traps heat in the same way as glass traps heat in a greenhouse. 

Question - Which gases are responsible for the greenhouse effect?

Answer - Major Greenhouse gases are:  

  • Carbon dioxide 
  • Nitrous oxide
  • Methane
  • Tropospheric Ozone
  • Water Vapour
  • Chlorofluorocarbons 

Question - What are the Main causes of the greenhouse effect?

Answer - Deforestation, Burning of fossil fuels, Industrialisation, Increase air pollution, Volcanic eruptions, and farming all contribute to producing greenhouse gases that absorb radiated heat from the sun, thereby increasing the temperature of the atmosphere. 

Question- What are the effects of Global Warming?

Answer - There will be changes in climatic conditions at local, regional and global levels with environmental, social, economic and political effects. The main ecological effects will be as follows: 

  • Changes in the composition of atmospheric gases due to increased levels of carbon dioxide and resulting global heat imbalance.
  • Rise in the temperature of the earth’s surface, oceans and lower atmosphere.
  • The hydrological cycle would be disturbed. A decrease in precipitation and soil moisture content in most agricultural regions of the world is observed.
  • Melting of the continental and polar glaciers, icebergs, ice caps etc. resulting in a rise in sea level. This in turn would submerge many islands and coastal ecosystems.
  • Global warming itself would increase ozone depletion.

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