Global warming
The role of greenhouse gases
greenhouse gases are essential for life on Earth - carbon dioxide, water
vapour, ozone, methane…
- they raise the temperature of the atmosphere by about 33ºC
- they allow shortwave radiation from the sun to pass through, but
they also act as an insulating layer; they prevent reflected
longwave radiation from escaping from the atmosphere ---> raises
the surface temperatures (and the lower atmosphere)
- concerns about enhanced greenhouse effect: the over-emission of
greenhouse gases as a result of human activity
● CO2 levels have risen from 315 parts per million in 1950 to
an expected 600ppm by 2015 - increase due to human
activity:
➢ burning fossil fuels
➢ deforestation - also removes the trees which convert
CO2 into oxygen
● Methane: second largest contributor to global warming -
increasing at a rate of 0.5 - 2% each year.
➢ cattle give off 65 - 85 million tonnes per year
➢ natural wetlands + paddy fields = 150 million
tonnes/year
➢ bogs trapped in permafrost will melt as a result of
global warming ---> methane emissions
➢ rice production
● Chlorofluorocarbons (CFCc): synthetic chemicals that
destroy ozone - absorb outgoing longwave radiation
➢ increasing at a rate of 6%/year
➢ 10,000x more efficient at trapping heat than CO2
- human activities are disturbing the natural balance of greenhouse
gases in the atmosphere
, How human activities add to greenhouse gases
evidence shows that - in between ice ages and interglacial periods -
changes in the composition of greenhouse gases in the atmosphere
were the reason for the large global temperature swings ---> 5ºC - 7ºC
studies in Hawaii 1957 ---> trend in CO2 level = annual pattern,
influenced by the seasonal changes in vegetation.
1970: new trend; long-term increase in CO2 levels.
1980: 5,000 million tonnes of CO2 burned every year - ½ of it absorbed
by natural sinks (vegetation, plankton…)
main reasons for increase in the levels of CO2:
- burning fossil fuels
- disruption to rainforests - Amazon fires
- change in albedo - affects the amount of solar energy absorbed
by Earth's surface
- Aerosols made from sulphur - can modify clouds and act at low
temperatures
- change in ozone in the stratosphere - mainly due to CFCs
Albedo: the percentage of radiation that any surface reflects as a ratio of
the total radiation it receives.
- clear surfaces have a higher albedo than darker ones
- average albedo on Earth is 37 - 39% of the shortwave radiation from
the Sun
Arguments surrounding global warming
natural causes of global warming + climate change
- variations in Earth's orbit around the Sun
- variations in the tilt of the Earth's axis
- variations in solar output - level of shortwave radiation
- changes in the amount of dust in the atmosphere - partly due to
volcanic activity
The role of greenhouse gases
greenhouse gases are essential for life on Earth - carbon dioxide, water
vapour, ozone, methane…
- they raise the temperature of the atmosphere by about 33ºC
- they allow shortwave radiation from the sun to pass through, but
they also act as an insulating layer; they prevent reflected
longwave radiation from escaping from the atmosphere ---> raises
the surface temperatures (and the lower atmosphere)
- concerns about enhanced greenhouse effect: the over-emission of
greenhouse gases as a result of human activity
● CO2 levels have risen from 315 parts per million in 1950 to
an expected 600ppm by 2015 - increase due to human
activity:
➢ burning fossil fuels
➢ deforestation - also removes the trees which convert
CO2 into oxygen
● Methane: second largest contributor to global warming -
increasing at a rate of 0.5 - 2% each year.
➢ cattle give off 65 - 85 million tonnes per year
➢ natural wetlands + paddy fields = 150 million
tonnes/year
➢ bogs trapped in permafrost will melt as a result of
global warming ---> methane emissions
➢ rice production
● Chlorofluorocarbons (CFCc): synthetic chemicals that
destroy ozone - absorb outgoing longwave radiation
➢ increasing at a rate of 6%/year
➢ 10,000x more efficient at trapping heat than CO2
- human activities are disturbing the natural balance of greenhouse
gases in the atmosphere
, How human activities add to greenhouse gases
evidence shows that - in between ice ages and interglacial periods -
changes in the composition of greenhouse gases in the atmosphere
were the reason for the large global temperature swings ---> 5ºC - 7ºC
studies in Hawaii 1957 ---> trend in CO2 level = annual pattern,
influenced by the seasonal changes in vegetation.
1970: new trend; long-term increase in CO2 levels.
1980: 5,000 million tonnes of CO2 burned every year - ½ of it absorbed
by natural sinks (vegetation, plankton…)
main reasons for increase in the levels of CO2:
- burning fossil fuels
- disruption to rainforests - Amazon fires
- change in albedo - affects the amount of solar energy absorbed
by Earth's surface
- Aerosols made from sulphur - can modify clouds and act at low
temperatures
- change in ozone in the stratosphere - mainly due to CFCs
Albedo: the percentage of radiation that any surface reflects as a ratio of
the total radiation it receives.
- clear surfaces have a higher albedo than darker ones
- average albedo on Earth is 37 - 39% of the shortwave radiation from
the Sun
Arguments surrounding global warming
natural causes of global warming + climate change
- variations in Earth's orbit around the Sun
- variations in the tilt of the Earth's axis
- variations in solar output - level of shortwave radiation
- changes in the amount of dust in the atmosphere - partly due to
volcanic activity
