Greenhouse gases and climate change

In a nutshell

Climate change is complex and is affected by different factors, such as greenhouse gases and other pollutants. Human activity affects climate change directly. Climate change impacts: the environment, habitats and livelihoods.

Global warming

Definition

Climate change is global, long-term changes in weather patterns and temperature, a key aspect of climate change is global warming. Global warming refers to an increase in the Earth's average temperature.

The greenhouse gas effect

Greenhouse gases (atmospheric gases that absorb infrared radiation) prevent thermal energy from escaping back to space, which causes the Earth's surface to become warmer.

The greenhouse gas effect is required, as otherwise all heat would be re-emitted back to space and the Earth would be too cold for most species to survive. However, human activity has led to an unusual increase in the greenhouse gas effect, which has led to global warming and climate change.

Example

Examples of greenhouse gases are: carbon dioxide ( $CO_2$ ), methane ( $CH_4$ ), water vapour ( $H_2O$ ) and nitrous oxide ( $N_2O$ ).

PROCEDURE

1.	Electromagnetic radiation is emitted by the sun, reaching the Earth's atmosphere.
2.	Most of this is re-emitted back to space.
3.	Some heat, in the form of infrared radiation, is absorbed by greenhouse gases in the Earth's atmosphere; this is the greenhouse gas effect.

Human activity

Greenhouse gas emissions have been increasing since 1750. Humans have contributed to this by:

Combustion of fossil fuels produces nitrous oxide and carbon dioxide.
Deforestation (widespread clearing of trees) means there are less trees to absorb carbon dioxide.
Nitrogen containing fertilisers increase nitrous oxides emissions.
Large-scale farming of cows increases methane emissions.

Effects of global warming

Global warming has serious consequences. These include:

Changes in the patterns and intensities of precipitation.
Increased frequency of extreme weather events.
Loss of habitats due to extreme weather events.

Example

Why does global warming increase the frequency and intensity of floods?

1.	At higher temperatures water molecules in bodies of water, such as rivers and oceans, gain more kinetic energy. This increases the rate of evaporation. Hence, more water vapour will rise and condense, forming clouds, eventually falling as precipitation.
2.	Since more water is incorporated into the clouds, the rate and intensity of precipitation increases. This increases the likelihood of flooding.
3.	Moreover, water vapour itself is a greenhouse gas so its increased presence in the atmosphere contributes further to global warming. This is a positive feedback loop.
4.	Rising sea levels is another cause of flooding. Ice caps and glaciers melt, which increases the volume of water, causing sea levels to rise.
5.	Heating of the sea itself causes water molecules to move further apart due to increased kinetic energy; this is called thermal expansion and contributes to sea level rise.