Water vapour is one of the important greenhouse gas which is in the state of water when it is in the hydrosphere. 95% of greenhouse gases are water vapour. Water vapour is the most abundant greenhouse gas on Earth responsible for around half of the greenhouse effect on Earth. An increase in greenhouse gases like carbon dioxide and methane lead to an increase in temperature which further increases evaporation from both water and land areas. Water vapour levels in the atmosphere rise as a result of higher evaporation and because warmer air holds more water, this contributes to further warming. In this article, we will discuss Water Vapour as a Greenhouse Gas which will be helpful for UPSC exam preparation.

Water Vapour as Greenhouse Gas

• Water vapour is nothing but water in gaseous form.
• Water vapour is produced by the evaporation or boiling of liquid water, or by the sublimation of ice.
• Water vapour is the most significant overall contributor to the greenhouse effect, and humans are not directly responsible for emitting enough of this gas to change its concentration in the atmosphere.
• Under normal atmospheric conditions, water vapour is continuously produced by evaporation and removed by condensation.
• It is less dense and causes convection currents that can lead to clouds.
• Water vapour, like most atmospheric constituents, is transparent.
• It works as a blanket, keeping the earth from becoming too cold or too hot.
• It also adds to the stability and instability of the air.
• It is an effective greenhouse gas because it absorbs longwave radiation and radiates it back to the surface, contributing to warming as well as greenhouse effect.
• Water vapour is the most abundant greenhouse gas in the atmosphere, both in terms of weight and volume.
• Unlike CO2, water vapour moves quickly through the atmosphere, evaporating and condensing.
• Because evaporation rates increase with temperature, the amount of water vapour in the air at any given time (and the amount of warming it causes) is strongly related to the amount of other greenhouse gases in the air.
• Water vapor concentrations are generally higher near the equator and over oceans, where evaporation is more significant, and lower over land and at higher latitudes.

Significance of Water Vapour

• Water vapour is crucial to the thermal radiation balance and the hydrological cycle.
• It is a key component in atmospheric thermodynamics because it transfers latent heat, and contributes to absorption and emission in a range of groups.
• It condenses into clouds that reflect and absorb solar radiation, affecting the energy balance directly.

Properties of Water Vapour

Evaporation

• Evaporation is the process through which a water molecule changes from a liquid to a gaseous state.
• During evaporation, each water molecule absorbs or releases kinetic energy.
• The capacity of air to absorb and hold water increases as temperature rises.
• Air movement replaces the saturated layer with the unsaturated layer.
• As a result, the more the air movement, the larger the evaporation.

Sublimation

• Sublimation is the process by which a substance changes from the solid to the gaseous phase without changing to the liquid phase.
• Sublimation is responsible for the gradual disappearance of ice and snow in the middle of winter when temperatures are too low to cause melting.

Condensation

• Condensation is the change of water vapour to water.
• Condensation in the atmosphere causes clouds, fog, and precipitation.
• When water vapour condenses on a surface, it causes net warming of that surface. Heat energy is carried by the water molecule.
• As a result, the temperature of the atmosphere falls slightly.

Role of Water Vapour in Atmosphere

• Water vapour remains in the atmosphere for a considerably shorter amount of time than other greenhouse gases.
• When the amount of water vapour in the atmosphere increases, then warm air can hold more moisture.
• As a result, the climate warms, air temperatures rise further, and more evaporation from water and land occurs thus increasing more moisture in the atmosphere and the cycle continues contributing to warming. This further amplifies the greenhouse effect.

Effect of Water Vapour on Global Water Cycle

• The global water cycle is also accelerated by increases in atmospheric water vapour. They help to make wet areas wetter and dry areas drier.
• The more water vapour there is in the air, the more energy it contains. This energy fuels violent storms, especially over land. As a result, more extreme weather events occur.
• However, increased evaporation from the land also dries out soils. When heavy rains fall on hard, dry ground, the water runs off into rivers and streams rather than dampening soils. This increases the likelihood of drought.
• In short, when increased levels of other greenhouse gases combine with atmospheric water vapour, the effects on Earth's climate are significant.

Recent Findings

• According to the Intergovernmental Panel on Climate Change's Sixth Assessment Report, total atmospheric water vapour is increasing by 1 to 2 percent per decade.
• According to thermodynamic laws, the amount of water vapour in the atmosphere can increase by about 7% for every degree Celsius increase in Earth's atmospheric temperature.
• It is believed that water vapour is the primary cause of Earth's current warming.
• However, increased water vapour does not contribute to global warming. Instead, it is a result of it.
• Increased atmospheric water vapour amplifies the warming caused by other greenhouse gases.

Conclusion

Water vapour is the most substantial natural greenhouse gas in the atmosphere and has a significant impact on water and climate. Water vapour is frequently discussed and acknowledged as an important component of the global warming process. When compared to the addition of carbon dioxide alone, the water vapour feedback process is most likely responsible for a doubling of the greenhouse effect.

FAQs

MCQs

1. Which of the following greenhouse gases is most abundant in Earth's atmosphere?

A) Carbon dioxide
B) Methane
C) Water vapor
D) Nitrous oxide

2. What is the primary source of water vapor in the atmosphere?

A) Oceans and lakes
B) Volcanic eruptions
C) Industrial emissions
D) Forest fires

3. How does water vapor contribute to climate change?

A) It absorbs UV radiation
B) It reflects sunlight
C) It enhances the greenhouse effect
D) It decreases atmospheric temperature

4. What is the relationship between water vapor and the temperature of Earth's atmosphere?

A) Higher temperature leads to more water vapor
B) Higher temperature leads to less water vapor
C) Water vapor causes temperature changes
D) Water vapor does not affect temperature

5. Which of the following gases is considered a feedback greenhouse gas?

A) Carbon dioxide
B) Water vapor
C) Nitrous oxide
D) Methane

GS Mains Questions and Model Answers

Q1: Analyze the role of water vapor in the greenhouse effect and its feedback mechanism in the context of climate change.

Answer: Water vapor plays a crucial role in the greenhouse effect, accounting for a significant portion of the Earth's warming. It is a feedback greenhouse gas, meaning its concentration increases as a result of rising temperatures caused by other greenhouse gases like carbon dioxide. As the Earth warms, more water evaporates from oceans and other water bodies, increasing water vapor in the atmosphere. This enhances the greenhouse effect, trapping more heat and causing further warming. The feedback loop between water vapor and temperature is one of the key mechanisms that accelerate climate change.

Q2: Discuss the significance of water vapor in regulating Earth's climate and its interaction with other greenhouse gases.

Answer: Water vapor is a key component in regulating Earth's climate due to its ability to absorb and re-radiate heat. While it is not the primary driver of climate change, its role as a feedback mechanism is crucial. Water vapor amplifies the warming effect caused by other greenhouse gases, particularly carbon dioxide and methane. This interaction increases the overall greenhouse effect, raising global temperatures. In addition, water vapor contributes to the formation of clouds, which can either cool the planet by reflecting sunlight or warm it by trapping heat, depending on cloud type and altitude.

Q3: What are the implications of increasing water vapor in the atmosphere due to global warming?

Answer: Increasing water vapor in the atmosphere due to global warming creates a positive feedback loop that exacerbates climate change. As the Earth's surface warms from the effects of greenhouse gases like carbon dioxide, more water evaporates into the atmosphere, leading to higher concentrations of water vapor. This, in turn, traps more heat, leading to further warming and more evaporation. This feedback mechanism accelerates global warming, making it more difficult to mitigate the effects of climate change. Additionally, increased water vapor contributes to more extreme weather patterns, including heavier rainfall and more intense storms.

Previous Year Questions on Water Vapor as a Greenhouse Gas

1. UPSC CSE Prelims 2020:

Question: Which of the following is a feedback greenhouse gas?

A) Carbon dioxide
B) Water vapor
C) Nitrous oxide
D) Methane

Answer: (B)

Explanation: Water vapor is a feedback greenhouse gas because its concentration in the atmosphere is directly linked to temperature. It amplifies the warming caused by other greenhouse gases.

2. UPSC CSE Mains 2019 (GS Paper 3):

Question: Discuss the role of water vapor in the context of climate change and its interaction with other greenhouse gases.

Answer: Water vapor amplifies the greenhouse effect, enhancing the warming caused by other gases like carbon dioxide. As temperatures rise, more water evaporates, adding to the water vapor content in the atmosphere. This positive feedback loop accelerates global warming and contributes to climate change.