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8.6 – Global Warming

8.6.1 – Describe some possible models of global warming.

Records showing the history of the Earth’s temperature have illustrated the apparent

existence of global warming in the past few hundred years. There are a number of complex

atmospheric models currently in existence, including:

Changes in the composition of greenhouse gases in the atmosphere, due to

increased human combustion of fossil fuels and the natural diffusion of CO2 and

water vapour from oceans

Increased solar flare activity

Cyclical changes in the Earth’s orbit

Volcanic activity

Continental drift affecting the ocean currents and winds

8.6.2 – State what is meant by the enhanced greenhouse effect.

Greenhouse gas emissions from the burning of fossil fuels has increased the concentration

of carbon dioxide, nitrous oxides and CFC’s in the atmosphere, and the melting of

permafrost regions in the world and deforestation have increased levels of methane, which

then leads to infrared radiation increasing temperatures. The enhanced greenhouse effect is

the increase in greenhouse gasses in the atmosphere due to human activities.

8.6.3 – Identify the increased combustion of fossil fuels as the likely major cause of the

enhanced greenhouse effect.

Although still under investigation, Intergovernmental Panel on Climate Change (IPCC)

released a report stating that they believed that the observed increase in global

temperatures is likely due to human activities, such as the increased burning of fossil fuels

and the release of Carbon Dioxide.

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8.6.4 – Describe the evidence that links global warming to increased levels of greenhouse

gases.

Each year, as snow falls on the Arctic Circle, the atmospheric concentrations of gasses that

were present in that year are retained in the snow. This means that through interpretation

of arctic ice core drills, scientists are able to observe the fluctuations in atmospheric

temperature and greenhouse gas concentrations. Ice cores showing up to 420,000 years of

snowfall have been drilled in the Russian Antarctic base, Vostok, and these samples present

a correlation between global temperature and atmospheric greenhouse gas concentrations.

Additionally, tree rings can provide information into seasons and water precipitation levels

during the growth of the tree, and sedimentary records can be used to identify the seasonal

fluctuations in water levels of lakes. Core samples taken from the seabed of oceans can

establish a continuous and accurate record of historical surface sea-temperatures.

8.6.5 – Outline some of the mechanisms that may increase the rate of global warming.

There are a number of mechanisms that can increase the rate of global warming. These

include the following factors:

Due to the melting of ice, more of the Earth’s surface is covered by water as a result

of rising sea levels. Because of the positive feedback generated by the decrease in

albedo, more ice melts into water, which again lowers the albedo, causing the

temperature to rise, melting more ice.

The rising sea level as a result of the ice melting also causes a higher evaporation of

water vapour. As a greenhouse gas, the water vapour will continue heat the

atmosphere.

Higher temperatures in the water reduces the solubility of CO2, allowing less to

diffuse from the atmosphere into the water.

Changing forests to dry land through deforestation causes an increase in albedo,

causing more radiation to be reflected back to the atmosphere rather than absorbed

and used in carbon fixation. Burning the trees after they have been cut down also

increases the presence of CO2 in the atmosphere.

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8.6.6 – Define coefficient of volume expansion.

The coefficient of volume expansion is the fractional change in volume per degree change in

temperature.

Sea level rises are not only due to the melting of ice, but also because of the higher volume

taken up by water. Water is at its highest density (lowest volume) at 4oC, as it contracts

between 0 and 4oC, then expands at temperatures higher than 4oC.

Given a volume at a temperature of , the volume after a temperature change of will

increase by given by

Where is the coefficient of volume expansion, in K-1 or oC-1.

8.6.7 – State that one possible effect of the enhanced greenhouse effect is a rise in mean

sea level.

Changes in mean sea level affect the amount of water that can evaporate and the amount

of thermal energy that can be exchanged with the atmosphere. Also, changes in sea level

can affect ocean currents, which can influence the dispersal of heat between warm and cold

water.

8.6.8 – Outline possible reasons for a predicted rise in mean sea level.

The change in sea level is a natural occurrence caused by varying atmospheric pressure,

plate tectonic movements, wind, tides, increased rainfall, flow of large rivers into oceans

and changes in water salinity. However, an increase in the greenhouse effect could lead to

increase in Earth’s temperature, which would melt ice and snow causing the water level to

rise. It is important to notice that when the ice on water melts it does not result in a change

in sea level, as the weight of the ice is equal to the weight of the displaced water, and so

when the ice melts it will occupy a volume equal to the volume of the displaced water. As

such, only the melting of ice on land will result in a change of sea level.

Precise predictions are difficult to make due to factors such as:

Anomalous expansion of water

Different effects of ice melting on sea water compared to ice melting on land

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8.6.9 – Identify climate change as an outcome of the enhanced greenhouse effect.

We have seen from charts of CO2 levels and temperature from the past that a correlation

exists between the two. As there has been a significant increase in the emission of

greenhouse gases in the past hundred years, we can infer that the recent change in climate

is a result of the release of greenhouse gasses, the enhanced greenhouse effect.

8.6.10 – Solve problems related to the enhanced greenhouse effect.

E.G. a) The area of the Earth’s oceans is around 3.6×108 km2, with an average depth of

3.7 km. Assuming the coefficient of volume expansion of water of 2×10-4 K-1, estimate the

expected rise in sea level due to a temperature increase of 2 K

Therefore, the increase in volume:

So, the change in height:

b) Radiation of intensity 340 Wm-2 is incident on a lake of depth 50 m. Determine the

time required to increase the water temperature by 1 K.

By recognising that the power per area incident on the lake = 340 Wm-2, we know that

Therefore:

( )

As such, power per unit area is:

Therefore, change in temperature per time is equal to:

So, to find the time taken, the reciprocal is:

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8.6.11 – Identify some possible solutions to reduce the enhanced greenhouse effect.

Some measures that nations and individuals alike can take onboard to reduce the emission

of greenhouse gases and thus reduce the rate of global warming include:

Using fuel efficient cars and developing hybrid cars further

Increasing the efficiency of coal power plants or replacing with natural gas power

plants

Capturing the CO2 emitted by fossil fuel power plants (Carbon Capture)

Increasing use of renewable energy sources, including nuclear, solar, wind and

hydroelectric power

Stopping deforestation

Being conscious of energy usage

8.6.12 – Discuss international efforts to reduce the enhanced greenhouse effect.

A number of panels and self-imposed regulations have been introduced in an attempt to

decrease the emission of greenhouse gases. Some of these committees include:

Intergovernmental Panel on Climate Change (IPCC): countries and organisations that

regularly assess the current evidence from international research into global

warming and the human induced greenhouse effect.

Kyoto Protocol: In 1997, in Kyoto, Japan, an agreement towards cutting greenhouse

gases was reached, with the target of cutting greenhouse gas emissions by 5.2%

between 2008 and 2012. The protocol became legally binding when Iceland, the 55th

country to sign, joined the protocol.

Asia-Pacific Partnership on Clean Development and Climate (APPCDC): Six countries

that represent around 50% of the world’s energy use signed an agreement to work

together and with private sector partners to meet goals for energy security, national

air pollution reduction and climate change in ways that promote sustainable

economic growth and poverty reduction. These countries include Australia, China,

India, Japan, Korea and the United States.