4.4 Climate ChangeBy Max Lim, Chloe Wan & Jenny Cho

[4.4.1] Carbon dioxide and water vapour are the most significant greenhouse gases.● Greenhouse gases are gases in the atmosphere that retain

heat.● The greenhouse gases that have the largest warming

effect on the Earth are carbon dioxide and water vapour.Carbon dioxide (CO2)

● Carbon dioxide is released into the atmosphere by:o Cell respiration in living organismso Combustion of biomass and fossil

● Carbon dioxide is removed from the atmosphere by photosynthesis and by dissolving in the ocean.

[4.4.1] Carbon dioxide and water vapour are the most significant greenhouse gases.

Water vapor (H2O)● Water vapor is formed by:

o Evaporation from the oceans

o Transpiration in plants● Water vapor is removed from

the atmosphere by rainfall and snow (precipitation).

Methane (CH4)● 3rd most significant

greenhouse gas (after carbon dioxide and water vapour)

● Main component of natural gas● Emitted from marshes and

other waterlogged habitats, as well as from landfill sites where organic matter (e.g. manure) have been dumped.

[4.4.2] Other gases including methane and nitrogen oxides have less impact.

Nitrous oxides (N2O)● Major greenhouse gas and air

pollutant● Naturally present in the atmosphere● However, human activities such as

agriculture, fossil fuel combustion, wastewater management, and industrial processes are increasing the amount of N2O in the atmosphere.

● In 2013, N2O) accounted for about 5% of all U.S. greenhouse gas emissions from human activities.

[4.4.2] Other gases including methane and nitrogen oxides have less impact.

Factors that determine the warming impact of a greenhouse gas:● How readily the gas absorbs long-

wave radiation ● The concentration of the gas in the

atmosphere

The concentration of a gas depends on the rate at which it is released into the atmosphere and how long on average it remains there.

[4.4.3] The impact of a gas depends on its ability to absorb long-wave radiation as well as on its concentration in the atmosphere.

[4.4.3] The impact of a gas depends on its ability to absorb long-wave radiation as well as on its concentration in the atmosphere.

Type of greenhouse gas Lifetime in atmosphere

Carbon dioxide Can be as long as thousands of years

Water vapour 9 days

Methane 12 years

Nitrous oxide 114 years

[4.4.4] The warmed Earth emits longer-wave radiation (heat).

● Warmed surface of the Earth absorbs short-wavelength energy from the sun, then re-emits it at longer wavelengthso Solar radiation: peak wavelength = 400 nmo Re-emitted energy (infrared): peak wavelength =

10,000 nm

[4.4.5] Longer-wave radiation is reabsorbed by greenhouse gases which retains the heat in the atmosphere.

● 20-30% of short-wavelength radiation from the sun is absorbed in the atmosphereo This is mostly ultraviolet light,

which is absorbed by ozone● 70-75% of solar radiation hence

reaches the Earth’s surface, of which most is converted into heat

● A much higher percentage (70-75%) of longer-wavelength radiation re-emitted by the surface of the Earth is reabsorbed by greenhouse gases

● This energy is then re-emitted, often back towards the surface of the Earth - this is an enhanced greenhouse effecto It is important to note that the greenhouse effect has

been used to trap energy in the Earth’s atmosphere, and is the primary reason of the Earth’s ability to sustain life - without this effect the mean temperature on the Earth’s surface would be 255K, or -18°C

[4.4.5] Longer-wave radiation is reabsorbed by greenhouse gases which retains the heat in the atmosphere.

[4.4.6] Global temperatures and climate patterns are influenced by concentrations of greenhouse gases

● The surface temperature of the Earth would be an average of 32°C lower without the greenhouse effect

● If there is a rise in concentration of greenhouse gases, more re-emitted radiation will be reabsorbed, and hence we can expect a general increase in global temperatures

● However, this doesn’t mean the relationship between concentration of greenhouse gases and rise in global temperatures is directly proportionalo Other factors also play a significant role, including the

Milankovitch cycles and Earth’s orbital variations

[4.4.6] Global temperatures and climate patterns are influenced by concentrations of greenhouse gases

● Global temperatures affect wide ranging aspects of Earth’s climateo Increased temperatures results in increased evaporation,

leading to more frequent periods of rain with increased amounts of rain

o Distribution of rainfall will also change dramatically - some areas will experience droughts whilst other areas might experience intense flooding and rainfall.

[4.4.6] Global temperatures and climate patterns are influenced by concentrations of greenhouse gases

● Higher ocean temperatures, as a result of increased global temperatures, could cause stronger storms and hurricanes with significantly faster wind speeds

[4.4.7] Industrialization and climate change

This graph shows the atmospheric carbon dioxide concentrations over the past 800,000 years.

It indicates that there have been large fluctuations.

[4.4.7] Industrialization and climate change● Atmospheric carbon dioxide concentrations were between 260

and 280 ppm until the late 18th century- this is probably when concentrations started to rise above natural

levels ● Late 18th century → industrial revolution was starting in some

countries- main impact of industrialization globally was in the 2nd half of

20th century- combustion of coal, oil and natural gas increased rapidly than

ever before- this lead to increases in atmospheric carbon dioxide

concentration

● There is strong evidence for a correlation between atmospheric carbon dioxide concentration and global temperatures since the start of the industrial revolution

- however, there are other factors that have an effect

[4.4.8] Burning fossil fuels● As the industrial revolution spread, increasing quantities of

coal were being mined and burned, causing carbon dioxide emissions

● The combustion of coal provided a source of heat and power

● During the 19th century, the combustion of oil and natural gas became increasingly widespread in addition to coal

[4.4.8] Burning fossil fuels

● Increases in burning fossil fuels were most rapid from 1950s onwards → this coincides with the period of steepest rises in atmospheric carbon dioxide

● Therefore it can be seen that increases in atmospheric carbon dioxide are largely due to increases in the combustion of fossilized organic matter