Image Source Mar 05, 2021 00:26 IST , Updated: Jul 14, 2021 00:26 IST · 5 min read
What is greenhouse effect ?
The greenhouse effect is the natural warming of the earth that results when gases in the atmosphere trap heat from the sun that would otherwise escape into space.The greenhouse effect is a good thing, it warms the planet to its comfortable average of 15 degrees celsius and keeps life on earth, well, livable. Without it the world would be a frozen (-18 °C), uninhabitable place, more like Mars.
The problem is, human activities, mainly the burning of fossil fuels and clearcutting of forests, have increased the greenhouse effect and caused global warming.
How it works ?
Solar radiation reaches the Earth's atmosphere, some of this (30 percent) is reflected back into space. Approximately 70 percent passes through the atmosphere to the earth's surface, where it is absorbed by the land, oceans, and atmosphere, and heats the planet.This heat (~70 percent reaching to surface) is then radiated back up in the form of invisible infrared light; some 90 percent of it, gets absorbed by atmospheric gases, known as greenhouse gases, and redirected back toward the earth, causing further warming.
In the greenhouse effect, shortwave solar radiation passes through the atmosphere and reaches the Earth's surface where it gets absorbed. When the radiation is re-emitted by the Earth, it is now in the form of long wavelength, infrared radiation, which does not easily pass through the atmosphere.
What are greenhouse gases ?
A greenhouse gas (GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect.The most significant gases that cause global warming via the greenhouse effect are the following:
1) Carbon Dioxide
Carbon Dioxide (CO2) is the primary greenhouse gas, it is most dangerous and prevalent greenhouse gas, responsible for about three-quarters of emissions. It can linger in the atmosphere for thousands of years.Carbon Dioxide (CO2) accounts for about 76 percent of global human-caused emissions, it sticks around for quite a while.
The vast majority of anthropogenic carbon dioxide emissions come from combustion of fossil fuels, principally coal, petroleum and natural gas, with additional contributions coming from deforestation and other changes in land use.
2) Methane
It accounts for about 16 percent of all greenhouse gas emissions and is second biggest contributor to human-caused global warming after CO2.Although methane (CH4) persists in the atmosphere for far less time than carbon dioxide, it is much more potent (84-86 times stronger than CO2) in terms of the greenhouse effect.
The leading source of anthropogenic methane emissions is agriculture (grazing animals), closely followed by gas venting and fugitive emissions from the fossil-fuel industry. Traditional rice cultivation is the second biggest agricultural methane source after livestock.
It is typically destroyed through chemical reactions that produce CO2 and water, a relatively small portion is also consumed by bacteria in soils.
On Earth, hydrothermal vents on seafloors are known to release methane, but this happens at a very slow rate.
Methane-producing organisms on Earth
Most of the methane on Earth has a biological origin.Microorganisms called methanogens are capable of generating methane as a metabolic byproduct. They do not require oxygen to live and are widely distributed in nature.
They are found in swamps, dead organic matter, and even in the human gut.
They are known to survive in high temperatures and simulation studies have shown that they can live in Martian conditions.
Methanogens have been widely studied to understand if they can be a contributor to global warming.
3) Nitrous Oxide
N2O is a long-lived greenhouse gas (GHG) and an ozone-depleting substance, with an atmospheric lifetime of 110-120 years. It is the third most important GHG, leading human-driven climate change, after carbon dioxide and methane.Nitrous oxide (N2O) accounts for about 6 percent of human-caused greenhouse gas emissions worldwide. It is a powerful greenhouse gas and has a GWP (Global warming potential) 300 times that of carbon dioxide on a 100-year time scale
Agriculture and livestock, including fertilizer, manure, and burning of agricultural residues, along with burning fuel, are the biggest sources of nitrous oxide emissions.
4) Fluorinated Gases
Fluorinated Gases are man-made gases emitted from a variety of manufacturing and industrial processes. There are four main categories: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3).Fluorinated gases are emitted in smaller quantities than other greenhouse gases (2 percent of man-made global greenhouse gas emissions), they trap substantially more heat.
5) Water Vapor
Water Vapor is the most abundant greenhouse gas overall. It differs from other greenhouse gases, because it changes in its atmospheric concentrations are linked not to human activities directly, but rather to the warming that results from the other greenhouse gases we emit.Warmer air holds more water and since water vapor is a greenhouse gas, more water absorbs more heat, inducing even greater warming.
Greenhouse Gases Source
The burning of coal, oil, and natural gas accounts for one-quarter of worldwide human-driven emissions, making it the largest single source.About another quarter of global greenhouse gas emissions stem from agriculture and other land-use activities such as deforestation. Vast majority is methane produced as manure decomposes and nitrous oxide, often released with the use of nitrogen-heavy fertilizers.
About one-fifth of global human-driven emissions come from the industrial sector, which includes the manufacturing of goods and raw materials like cement and steel, food processing, and construction.
The burning of petroleum-based fuels (gasoline and diesel etc), stem primarily from burning natural gas and oil for heating and cooking, refrigerants from air-conditioning and refrigeration systems etc.
Is ozone a greenhouse gas?
Ozone is technically a greenhouse gas, but ozone is helpful or harmful depending on where it is found in the earth's atmosphere.Ozone occurs naturally at higher elevations in the atmosphere (the stratosphere) where it forms a layer that blocks ultraviolet (UV) light, which is harmful to plant and animal life, from reaching the earth's surface.
The protective benefit of stratospheric ozone outweighs its contribution to the greenhouse effect and to global warming.
However, at lower elevations of the atmosphere (the troposphere), ozone is harmful to human health.