Earth’s Atmosphere, Climate Change, and the Indian Monsoon

Posted on Sep 17, 2024 in Geology

Rocks

The lithosphere has various types of rocks. Rocks are naturally occurring, hard, consolidated, inorganic materials composed of one or a large number of minerals.

Types of Rocks

  1. Igneous: These rocks are formed by the solidification of magma in the Earth’s interior or lava on the surface. Igneous rocks are composed of primary minerals, which are predominantly silicates. Igneous rocks sometimes overlap with sedimentary and metamorphic rocks.
  2. Sedimentary: Sedimentary rocks are formed by precipitation from solutions and the consolidation of remnants of biotic components like plants and animals. These rocks contain both original primary minerals and altered, as well as newly synthesized, secondary minerals.
  3. Metamorphic: Also known as thermal rocks, they are formed from preexisting rocks (igneous or sedimentary) due to changes in temperature and pressure. These rocks are formed when magma intrudes through preexisting igneous or sedimentary rocks. Further, igneous and metamorphic rocks get weathered and form sediments. These sediments get deposited and ‘lithified’ into sedimentary rocks.

Indian Monsoon

A monsoon is a regional wind that blows toward land during a certain season and blows from the landmasses during other seasons. These winds blow in the opposite direction in summer and winter. Though monsoon winds blow over all parts of the world, they are well-developed over India and the Southeast Asian regions. The Indian subcontinent has two types of winds:

  1. South-West Monsoon
  2. North-East Monsoon

South-West Monsoon

  • The southeast trade winds originate from the Southern Hemisphere in the Indian Ocean. When these winds cross the equator, they get deflected to the right by the Coriolis force, becoming the southwest trade winds. These winds gather large quantities of moisture as they pass over the Indian Ocean.
  • As the southwest monsoon winds approach the Indian Peninsula, they are diverted into two branches: the Arabian Sea Branch and the Bay of Bengal Branch.
  • When the moisture-laden Arabian Sea branch reaches the southwestern side of India, it is blocked by the Western Ghats.
  • When the mountain range blocks the horizontal flow, the wind ascends along the slope of the mountain range, cools down, and forms clouds. These clouds then result in precipitation.
  • Kerala gets the southwest monsoon mostly during early June every year.
  • These winds then take a westward turn and continue their journey, spreading over the northern parts of India, bringing rains to these areas.
  • Monsoon winds normally reach Delhi in the first week of July and could last till the end of September/early October.

North-East Monsoon

  • The Inter-Tropical Convergent Zone (ITCZ) moves to the south of the equator when the position of the sun shifts to the Southern Hemisphere. This leads to the reversal of winds, and the winds start blowing from the northeastern direction towards the ITCZ. These winds are known as the northeast monsoon winds or the northeast trade winds.
  • Since northeast winds originate mainly from the landmasses of the northeastern region of India, they are relatively dry.
  • When these winds pass over the Bay of Bengal toward the south, they gather moisture and cause rainfall over parts of Odisha, Andhra Pradesh, and Tamil Nadu.
  • Cyclone formation is common over the Bay of Bengal during the northeast monsoon season. The cyclones also bring abundant rainfall over Odisha, Andhra Pradesh, Telangana, and Tamil Nadu.

Layers of the Atmosphere

Based on temperature, the atmosphere is divided into four parts:

  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere

Layers of the Atmosphere Explained

  1. Troposphere: The bottom, dense part of the atmosphere, containing 70 percent of its mass, close to the ground, is the troposphere. It reaches up to 11 km from the ground.
  2. Stratosphere: This layer extends to a height of about 50 km from the Earth’s surface.
  3. Mesosphere: The portion of the atmosphere above the stratosphere, between 50 km and 80 km, is known as the mesosphere.
  4. Thermosphere: The thermosphere extends from 80 km to about 60,000 km from Earth. Here, the temperature increases to about 2000°C.

Greenhouse Effects

Incoming Solar Radiation

The atmosphere behaves like a complex mega heat engine. A large number of processes, like air movements (storms and cyclones), evaporation and formation of clouds, precipitation, etc., take place in the atmosphere. Incoming solar radiation (insolation) supplies the required energy and drives these processes.

  • Only two-billionths of solar energy reaches Earth, of which only a small portion is responsible for physical and biological processes. The sun also emits solar winds consisting of charged particles like plasma, magnetic fields, etc.
  • Insolation contains X-rays, gamma rays, ultraviolet (UV) rays, visible light, infrared rays, microwaves, radio waves, and the like.
  • Of all the energy received by Earth, the UV, visible, and infrared portions constitute over 95 percent.
  • The harmful UV radiation is prevented from reaching Earth by the ozone layer. Parts of the long waves within solar radiation are absorbed in the troposphere.
  • The solar radiation that ultimately reaches Earth comprises mainly visible light, which is composed of seven colors.
  • While traveling through the atmosphere, a portion of the radiation energy is reflected by clouds, and some are scattered and absorbed by gases and particles.

Outgoing Radiation

  • If all the energy received by Earth were retained on its surface, the planet would be very hot and would become an uninhabitable place.
  • After the heating of its surface, the Earth reflects a certain amount of energy. Some of this heat energy is transmitted to the upper layers of air through conduction.
  • Conduction, in turn, initiates convection in the air above the Earth’s surface. The heat energy emitted from the Earth’s surface is in the form of long-wave radiation and is called outgoing radiation.
  • A portion of the outgoing radiation is absorbed by certain gases in the atmosphere. Gases capable of absorbing outgoing radiation are CO2, CO, water vapor, etc. They are called Greenhouse Gases (GHGs).
  • The amount of radiation absorbed is directly proportional to the concentration of gases.
  • Due to the effect of GHGs, Earth is prevented from cooling down drastically. GHGs thus act like a blanket and provide Earth with an ideal climate for life to flourish. This process is known as the greenhouse effect.
  • The intensity of the greenhouse effect varies from place to place, depending upon the concentration of GHGs.

Global Warming

  • Earth receives solar energy in abundance, heating its surface.
  • Some heat is radiated back into space.
  • Certain gases, known as Greenhouse Gases (GHGs), that include carbon dioxide, methane, nitrous oxide, ozone, etc., and water vapor prevent the heat from escaping the Earth’s atmosphere.
  • This leads to an increase in atmospheric temperature, known as the greenhouse effect. The greenhouse effect has its own positive effect. Without the greenhouse effect, the temperature of Earth would have been much cooler and covered with ice.
  • Recently, due to certain human activities, the quantity of GHGs has increased manifold.
  • The burning of large quantities of fossil fuels, deforestation, mining activities, agricultural activities, overall industrial activities, etc., has increased the concentration of GHGs around the globe.
  • This is aggravated by the reduction in green coverage. Certain natural processes, like volcanic eruptions, also contribute to GHG emissions. Chlorofluorocarbons (CFCs) like methane released from human and animal waste, garbage dumps, rice fields, etc., have caused large-scale depletion of the ozone layer.
  • The abnormal increase in the concentration of GHGs has led to global warming. The average temperature of the globe has become warmer over the last century.
  • This warming is, however, not uniform all over the globe. While the temperature is high in some places, it gets cooler in certain other places.
  • Over the last century, the overall temperature of the Earth’s atmosphere has become warmer by about 0.6 degrees Celsius (1.3 degrees Fahrenheit).
  • Evidence shows that the warming is happening much faster than it has in the past.
  • Further, there is new and stronger evidence suggesting that most of the observed warming over the last 50 years is attributable to anthropogenic reasons.
  • If GHG emissions continue at this rate, by 2030 the temperature will rise by 1.5°C to 4.5°C.
  • The Intergovernmental Panel on Climate Change (IPCC) states that the human-induced change in atmospheric chemistry will increase temperatures by 1.4°C to 5.8°C by the year 2100 (IPCC, 2001).
  • There have been a large number of apparent signs of global warming in many parts of the globe. A few of them include the melting of ice caps in the poles and the shrinking of glaciers in mountain ranges like the Alps, Andes, Himalayas, and Mount Kilimanjaro.