GREENHOUSE EFFECT: HOW IT IS PRODUCED, CAUSES, GASES, CONSEQUENCES - ENVIRONMENT - 2025

The greenhouse effect is a natural process in which the atmosphere retains part of the infrared radiation emitted by the Earth and thus heats it. This infrared radiation comes from the heating generated on the earth's surface by solar radiation.

This process occurs because the Earth as an opaque body absorbs solar radiation and emits heat. At the same time, since there is an atmosphere, the heat does not completely escape into outer space.

Greenhouse effect scheme. Source: Robert A. Rohde (Dragons flight at English Wikipedia), Translation into Spanish felix, adaptation layout Basquetteur

Part of the heat is absorbed and re-emitted in all directions by the gases that make up the atmosphere. Thus, the Earth maintains a certain thermal equilibrium that establishes an average temperature of 15 ºC, guaranteeing a variable range in which life can develop

The term "greenhouse effect" is a simile with greenhouses for growing plants in climates where the ambient temperature is lower than required. In these grow houses, the plastic or glass roof allows the passage of sunlight but prevents the exit of heat.

In this way, a warm microclimate favorable to the development of plants is maintained, regardless of the lower outside temperature.

The most relevant gases in the greenhouse effect are water vapor, carbon dioxide (CO2) and methane. Then, as a result of pollution generated by humans, other gases are incorporated and CO2 levels increase.

CO2 gases, water vapor and methane in the atmosphere

These gases include nitrogen oxides, hydrofluorocarbons, perfluorinated hydrocarbons, sulfur hexafluoride, and chlorofluorocarbons.

Is the greenhouse effect good or bad?

The greenhouse effect is fundamental for life on Earth as it guarantees the appropriate temperature range for its existence. Most biochemical processes require temperatures between -18ºC to 50ºC.

In the geological past there have been fluctuations in the earth's average temperature, either increasing or decreasing. In the last two centuries there has been a process of sustained increase in global temperature.

The difference is that currently the rate of increase is particularly high and seems to be associated with human activity. These activities generate greenhouse gases that accentuate the phenomenon.

What is the problem, then?

Humans have persistently added pollutants to the environment since the mid-18th century, as a result of industrialization. Among these pollutants is the emission of gases that contribute to the greenhouse effect, either because they absorb heat or damage the ozone layer.

The ozone layer is found in the upper part of the stratosphere and filters ultraviolet (higher energy) solar radiation. The more ultraviolet radiation, the more heat and in addition mutagenic effects can be generated.

On the other hand, heat-retaining gases such as CO2 and methane reduce emission heat loss from the Earth. While among the gases that damage the ozone layer are all fluorine and chlorine compounds.

The consequences of the increase in the greenhouse effect is an increase in the Earth's temperature. This in turn causes a series of climatic changes, including the melting of polar and glacial ice.

How is the greenhouse effect produced?

- Earth's atmosphere

Layers of the atmosphere

Understanding the basic elements of the chemical composition and structure of the atmosphere is fundamental to understanding the greenhouse effect.

Chemical composition of the Earth's atmosphere

Nitrogen (N) predominates in the composition of the Earth's atmosphere, 79% and Oxygen (O2) 20%. The remaining 1% is made up of various gases, of which the most abundant are Argon (Ar = 0.9%) and CO2 (0.03%).

These gases cannot absorb sunlight, that is, the short-wave energy emitted by the Sun (visible and ultraviolet spectrum).

Layers of the atmosphere

The highest proportion of atmospheric gases is concentrated in the strip that goes from the earth's surface to 50 km in height. This is so due to the attraction that the gravitational force makes on the gases that make up the atmosphere.

In these first 50 km of atmosphere, two layers are recognized, the first one from 0 to 10 km high and the second from 10 to 50 km high. The first is called the troposphere and concentrates approximately 75% of the gaseous mass of the atmosphere.

The second is the stratosphere that concentrates 24% of the atmospheric gaseous mass and in its upper part is the ozone layer. The ozone layer is key to understanding the greenhouse effect, as it is responsible for fixing the ultraviolet rays from the Sun.

Although three more layers extend above these layers of the atmosphere, the two lowest ones are the determining factors for the greenhouse effect.

- The greenhouse effect

The main elements of the process by which the greenhouse effect is produced are the Sun, the Earth and atmospheric gases. The Sun is the source of energy, the Earth the receiver of this energy and emitter of heat and gases play different roles according to their properties.

Solar energy

The Sun fundamentally emits high-energy radiation, that is, corresponding to the visible and ultraviolet wavelengths of the electromagnetic spectrum. The emission temperature of this energy reaches 6,000ºC, but most of it dissipates along the way.

Of the 100% of solar energy that reaches the atmosphere, about 30% is reflected to outer space (albedo effect). 20% is absorbed by the atmosphere, mainly by suspended particles and the ozone layer, and the remaining 50% warms the earth's surface. This video reflects this process:

The earth

Like any body, the Earth emits radiation, which in this case is long-wave radiation (infrared). The infrared radiation emitted by the Earth comes from its incandescent center (geothermal energy), but the emission temperature is low (almost 0 ºC).

However, the Earth receives solar energy that also heats it and emits additional infrared radiation.

On the other hand, the Earth reflects an important part of solar radiation due to its albedo (light tone or whiteness). This albedo is mainly due to clouds, bodies of water and ice.

Taking into consideration the albedo and the distance from the planet to the Sun, the Earth's temperature should be -18 ºC (effective temperature). The effective temperature refers to what a body should have only considering albedo and distance.

However, the real average temperature of the Earth is around 15ºC with a difference of 33ºC with the effective temperature. In this marked difference between the actual and effective temperature, the atmosphere plays a fundamental role.

The atmosphere

The key to the temperature of the Earth is its atmosphere, if it did not exist the planet would be permanently frozen. The atmosphere is transparent to much of the short-wave radiation, but not to a large proportion of the long-wave (infrared) radiation.

By letting solar radiation through, the Earth heats up and emits infrared radiation (heat), but the atmosphere absorbs some of that heat. In this way, the layers of the atmosphere and clouds become hot and emit heat in all directions.

Greenhouse effect

The process of global warming by atmospheric retention of infrared radiation is what is known as the greenhouse effect.

Greenhouse in Kew Gardens (England). Source:

The name comes from the agricultural greenhouses, where species that require a higher temperature than the existing one in the production area are grown. For this, these grow houses have a roof that allows the passage of sunlight but retains the heat emitted.

In this way, it is possible to create a warm microclimate for those species that require it in their growth.

Causes

Although the greenhouse effect is a natural process, it is altered by human action (anthropic action). Therefore, it is necessary to differentiate the natural causes of the phenomenon and anthropic alterations.

- Natural causes

Solar energy

Short-wave (high-energy) electromagnetic radiation from the Sun is what heats the Earth's surface. This heating causes the emission of long-wave (infrared) radiation, that is, heat, into the atmosphere.

Geothermal energy

The center of the planet is incandescent and generates additional heat than that caused by solar energy. This heat is transmitted through the earth's crust mainly through volcanoes, fumaroles, geysers and other hot springs.

Atmospheric composition

The properties of the gases that make up the atmosphere determine that solar radiation reaches the Earth and that infrared radiation is partially retained. Some gases such as water vapor, CO2, and methane are especially efficient at retaining atmospheric heat.

Natural contributions of greenhouse gases

Those gases that retain infrared radiation from warming of the Earth's surface are called greenhouse gases. These gases are produced naturally as CO2 that is contributed by the respiration of living beings.

The oceans also exchange large amounts of CO2 with the atmosphere and natural fires also contribute CO2. The oceans are a natural source of other greenhouse gases such as nitrogen oxide (NOx).

On the other hand, microbial activity in soils is also a source of CO2 and NOx. In addition, the digestive processes of animals contribute large amounts of methane to the atmosphere.

- Anthropogenic causes

Heat generation

Human activities not only contribute gases that increase the greenhouse effect, but also provide additional heat. Part of the heat supplied comes from the burning of fossil fuels and another from the decrease in the albedo effect.

Temperature distribution on the earth's surface. Source:

The latter is due to the greater absorption of solar energy by dark artificial surfaces such as asphalt. Various investigations have shown that large cities generate a net heat input of between 1.5 and 3 ºC.

Industrial activities

Industry in general emits additional heat into the atmosphere as well as various gases that affect the greenhouse effect. These gases can absorb and emit heat (ex: CO2) or destroy the ozone layer (ex: NOx, CFC and others).

Automotive traffic

Large concentrations of vehicles in cities are responsible for most of the CO2 added to the atmosphere. Automotive traffic contributes around 20% of the total CO2 generated by the burning of fossil fuels.

Production of electricity and heating

The burning of coal, gas and oil derivatives for the production of electricity and heating contributes almost 50% of the CO2.

Manufacturing and construction industry

Together, these industrial activities contribute almost 20% of the CO2 produced by burning fossil fuels.

Forest fires

Forest fires are also caused by human activities and annually release millions of tons of greenhouse gases into the atmosphere.

Waste dumps

The accumulation of waste and the fermentation processes that take place, as well as the burning of said waste, are a source of greenhouse gases.

farming

Agricultural activity contributes more than 3 million metric tons of methane gas annually to the atmosphere. Among the crops that contribute the most in this regard is rice.

In the case of rice, the methane contribution comes from the ecosystem generated by its cultivation system. This is because the rice is planted in a sheet of water, thus creating an artificial swamp.

In swamps, bacteria break down organic matter under anaerobic conditions producing methane. This crop can contribute up to 20% of the methane injected into the atmosphere.

Another crop whose management generates greenhouse gases is sugar cane, since it is burned before harvest and produces a large amount of CO2.

Ruminant livestock

Ruminants such as cows consume fibrous grass through fermentation processes carried out by bacteria in their digestive systems. Said fermentation releases 3 to 4 liters of methane gas into the atmosphere daily for each animal.

Only considering cattle, a contribution equivalent to 5% of greenhouse gases is estimated.

- Chain reaction

The increase in global temperature that causes the increase in greenhouse gases, induces a chain reaction. As the temperature of the oceans increases, the release of CO2 into the atmosphere increases.

Likewise, the melting of the poles and permafrost releases CO2 that has been trapped there. Also at higher ambient temperatures, there is a greater occurrence of forest fires and more CO2 is released.

Greenhouse gases

Some gases such as water vapor and CO2 act in the natural process of the greenhouse effect. For its part, the anthropic process involves other gases in addition to CO2.

Global trend curves of accumulation of different greenhouse gases. Source: Gases_de_efecto_invernadero.png: DouglasGreenderivative work: Ortisa (talk) derivative work: Ortisa

The Kyoto Protocol contemplates the emissions of six greenhouse gases, including carbon dioxide (CO2) and methane (CH4). Also, nitrous oxide (N2O), hydrofluorocarbon (HFC), perfluorinated hydrocarbon (PFC) and sulfur hexafluoride (SF6).

Water steam

Water vapor is one of the most important greenhouse gases for its ability to absorb heat. However, equilibrium is generated because water in liquid and solid state reflects solar energy and cools the Earth.

Carbon dioxide (CO2)

Carbon dioxide is the main long-lived greenhouse gas in the atmosphere. This gas is responsible for 82% of the increase in the greenhouse effect that has occurred in recent decades.

In 2017 the World Meteorological Organization reported a global CO2 concentration of 405.5 ppm. This represents an increase of 146% over the levels estimated for before 1750 (pre-industrial era).

Methane (CH

Methane is the second most important greenhouse gas, contributing about 17% of warming. 40% of methane is produced by natural sources, mainly wetlands, while the remaining 60% is generated by human activities.

Among these activities are ruminant farming, rice cultivation, fossil fuel exploitation and biomass combustion. In 2017 atmospheric CH4 reached a concentration of 1,859 ppm which is 257% higher than the pre-industrial level.

Nitrogen oxides (NOx)

NOx contribute to the destruction of stratospheric ozone, increasing the amount of ultraviolet radiation that penetrates the Earth. These gases originate from the industrial production of nitric acid and adipic acid as well as from the use of fertilizers.

By 2017, these gases reached an atmospheric concentration of 329.9 ppm, equivalent to 122% of the level estimated for the pre-industrial era.

Hydrofluorocarbons (HFCs)

These gases are used in various industrial applications to replace CFCs. However, HFCs also affect the ozone layer and have a very high active permanence in the atmosphere.

Perfluorinated hydrocarbon (PFC)

PFCs are produced in incineration facilities for the aluminum smelting process. Like HFCs, they have a high permanence in the atmosphere and affect the integrity of the stratospheric ozone layer.

Sulfur hexafluoride (SF6)

This gas also has a negative effect on the ozone layer, as well as high persistence in the atmosphere. It is used in high voltage equipment and in the production of magnesium.

Chlorofluorocarbons (CFCs)

CFC is a powerful greenhouse gas that damages stratospheric ozone and is regulated under the Montreal Protocol. However, in some countries such as China it is still used in various industrial processes.

What is the greenhouse effect for living beings?

- Boundary conditions

Life as we know it is not possible above certain temperature levels. Only some thermophilic bacteria are capable of inhabiting environments with temperatures above 100ºC.

Vital temperature

In general, the amplitude of temperature variation that allows most of the active life ranges from -18 ºC to 50 ºC. Likewise, life forms can exist in a latent state at temperatures of -200ºC and 110ºC.

Most species of animals and plants have even more restricted ranges of tolerance to room temperature.

- The dynamic balance of temperature

The greenhouse effect is a positive natural process for life on the planet, since it guarantees that vital range of temperature. But this is so as long as the proper balance is maintained between solar energy input and infrared radiation output.

The balance

Balance is guaranteed because nature produces almost as many greenhouse gases as it immobilizes. The ocean produces about 300 gigatons of CO2, but absorbs slightly more.

Likewise, the vegetation produces around 440 gigatons of CO2, at the same time that it fixes around 450.

Consequences of the greenhouse effect due to pollution

Anthropic pollution contributes extra amounts of greenhouse gases, breaking the natural dynamic balance. Although these amounts are much less than those generated by nature, they are enough to break this balance.

This has serious consequences for the planetary thermal balance and in turn for life on Earth.

Global warming

The increase in the concentration of greenhouse gases generates an increase in the global average temperature. In fact, the average global temperature is estimated to have risen 1.1 ° C since the pre-industrial era.

On the other hand, it has been indicated that the period from 2015 to 2019 has been the hottest on record so far.

Melting of the ice

The increase in temperature leads to the melting of polar ice and glaciers worldwide. This implies an increase in the sea level and the alteration of the marine currents.

Climate change

Although there is no full agreement on the process of climate change resulting from global warming, the reality is that the planet's climate is changing. This is evidenced in the alteration of marine currents, wind patterns and rainfall, among other aspects.

Population imbalances

The alteration of habitats due to the increase in temperature affects the population and biological behavior of the species. In some cases, there are species that increase their populations and expand their range of distribution.

However, those species that have very narrow temperature ranges for growth and reproduction can greatly reduce their populations.

Decrease in food production

Many agricultural and livestock areas see production reduced because the species are affected by the increase in temperature. On the other hand, ecological alterations result in the proliferation of agricultural pests.

Public health

Vector-borne diseases

As the planetary average temperature increases, some disease vector animals expand their geographic range. Thus, cases of tropical diseases are occurring beyond their natural range.

Shock

The increase in temperature can produce the so-called thermal shock or heat stroke, which implies extreme dehydration. This situation can cause serious organ failure, especially affecting children and the elderly.

Prevention and solutions

To prevent the increase in the greenhouse effect, it is necessary to reduce the emissions of the gases that cause it. This requires measures that range from public awareness, through national and international legislation, to technological changes.

However, according to the Intergovernmental Panel on Climate Change (IPCC), it is not enough to reduce emissions. In addition, it is necessary to reduce the current concentration of greenhouse gases in the atmosphere to stop global warming.

In this sense, a solution is to increase the vegetation cover to fix atmospheric CO2. Another is to implement technological air filtering systems to extract CO2 and fix it in industrial products.

So far, efforts to reach international agreements such as the Kyoto Protocol have not met their goals. On the other hand, technological developments to extract atmospheric CO2 are only at the prototype level.

Prevention

To prevent an increase in the greenhouse effect, it is necessary to reduce the production of greenhouse gases. This implies a series of actions that include the development of a citizen conscience, legislative measures, technological changes.

Awareness

A citizenry aware of the problem of global warming generated by the increase in the greenhouse effect is fundamental. In this way, the necessary social pressure is provided so that governments and economic powers take the required measures.

Legal framework

The main international agreement to tackle the problem of greenhouse gas generation is the Kyoto Protocol. However, so far this legal instrument has not been effective in reducing the rate of greenhouse gas emissions.

Some of the main industrialized countries with higher emission rates did not sign the extension of the protocol for its second term. Therefore, a stricter national and international legal framework is necessary if real effect is to be achieved.

Technological changes

Reengineering of industrial processes is required to reduce greenhouse gas emissions. Similarly, it is necessary to promote the use of renewable energies and reduce the use of fossil fuels.

On the other hand, it is essential to reduce the production of polluting waste in general.

Solutions

According to the experts, it is not enough to reduce greenhouse gas emissions, it is also necessary to reduce the current concentrations in the atmosphere. For this, various alternatives have been proposed that can use very simple or sophisticated technologies.

Carbon sinks

For this, it is recommended to increase the coverage of forests and jungles, as well as implement strategies such as green roofs. Plants fix atmospheric CO2 in their plant structures, extracting it from the atmosphere.

Carbon extraction pumps

Until now, extracting CO2 from the atmosphere is costly from an energy point of view and has a high economic cost. However, research is ongoing to find efficient ways to filter the air and remove CO2.

One of these proposals is already in the pilot plant phase and is being developed by the Universities of Calgary and Carnegie Mellon. This plant uses a solution of potassium hydroxide as a water trap and caustic calcium, through which the air is filtered.

In this process, the CO2 contained in the air is being retained, forming calcium carbonate (CaCO3). Subsequently, the calcium carbonate is heated and the CO2 is released, applying the resulting purified CO2 for industrial uses.

Bibliographic references

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