University of Bristol
Wellcome Trust
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PEEP for Physics & Ethics at GCSE
 

Pollution


Fossil fuels – greenhouse gases and the greenhouse effect.

The ‘greenhouse effect’

  • Most people regard the ‘greenhouse effect’ as one of the most serious environmental issues facing the earth.
    (To find out more about this effect, see the Climate change section)
  • In fact, the ‘greenhouse effect’ is a natural way to trap in heat by gases such as carbon dioxide and methane.
  • These gases are in the atmosphere and allow short-wave radiation but trap some of the long-wave radiation trying to escape, thus acting like the glass of a greenhouse .
  • Without this effect, the earth would have an average temperature of minus 17oC
  • To understand how the greenhouse effect works,  view this animation.

Why are there concerns?

  • The problem is that over the last few hundred years human activity has dramatically increased the quantities of these gases in the atmosphere, making the effect far more efficient at retaining heat.
  • This 'enhanced'  effect has been made worse by new ‘man-made’ gases which contribute to this effect (anthropogenic gases).
  • Although we are not certain, some scientists predict that there will be an average global temperature rise by 0.3oC every decade. This is investigated in more detail in the climate change section.
  • Some of these gases have a greater ability to retain radiation than others: e.g. one CFC (chloroflurocarbon) molecule is 5000 times more effective at reflecting radiation than one molecule of carbon dioxide.

The greenhouse gases:

The following table shows the major ‘greenhouse’ gases that have contributed to the ‘enhanced’ greenhouse effect. Water vapour, which is not included in the table, has the greatest greenhouse effect but it is not significantly affected by human activity.

 

Gas Conc
(ppm)
Average time spent in atmosphere (years) Source Why it has increased

CO2
Carbon
Dioxide

360

100

Burning of fossil fuels
Respiration

Growing demand for fossil fuels
Destruction of rainforests
Decline in global photosynthesis
Burning of cleared vegetation

CH4
Methane

1.7

10

Leaks from gas and oil fields
From ruminant stomachs
Rice cultivation (paddy fields)
Biomass burning
Landfill sites
Sewage treatment
Animal waste

More ruminants
Greater use of landfill
More paddy fields

N20
Nitrous
Oxide

0.3

130

Burning of fossil fuels
Denitrifying bacteria

Growing demand for fossil fuels
More fertiliser use
More land under cultivation

03
Ozone

0.01-0.05

Unknown

Car exhausts

More fossil fuels for transporrt

CFCs
Chlorfluro-
carbons

0.003

55-116

Coolants
Propellants
Expanders (foams)

More refrigerators etc. (Montreal Protocol has banned use of CFCs in developed countries.

ppm – parts per million

Solutions:

Solutions to the increase in ‘greenhouse’ gases is investigated in more detail in the ‘Climate change’ section.

Activities:      Read about the Kyoto Protocol. Is it working?

 

Next: Acid rain

 

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NOT RATED sophie 21-04-08 14:44
a very useful page