Studied by 2 peopleGreenhouse effect
Solar energy from the sun is trapped by the earth’s atmosphere, increasing temperature at the surface of the earth
Greenhouse effect is not inherently bad: without this, life on earth would not have been possible as temperature would have been too cold
Intensified/ enhanced greenhouse effect, where the greenhouse effect is augmented due to human activities, is widely believed to be the cause of climate change
CO2 and H2O vapour
Earth is essentially a closed system; not much escapes its gravity and atmosphere
C and H2O are recycled but the form that they take changes
CO2 and H2O vapour have the most significant impact on the greenhouse effect
Acts as an insulating layer that trap heat underneath the earth’s atmosphere
CO2
Released in the atmosphere:
Cellular respiration
Combustion of fossil fuels and biomass
Removed from atmosphere:
Photosynthesis
Dissolving into the oceans
H2O vapour
Released in the atmosphere:
Evaporation from oceans
Transpiration in plants
Removed from atmosphere:
Rainfall
Snow
Oxides and methane
Nitrous oxides is another significant greenhouse gas
Nitrous oxides are released by:
Bacteria in some habitats
Agriculture
Vehicle exhausts
Methane is the 3rd most significant greenhouse gas
Methane is emitted from:
Waterlogged habitats (peat)
Landfills
Fossil fuel extraction
Melting polar ice
Cattle
Warming effect of a gas
Two factors determine warming effect of a gas
How readily it absorbs long wave radiation
The conc- of gas in the atmosphere
E.g. methane traps 20X more heat than the equivalent amount of CO2 but is at much lower conc- in the atmosphere so contributes less to warming effect
Concentration of gas depends on
Rate at which it is realised into the atmosphere
How long it remains
E.g. water vapour is realised into the atmosphere very quickly, but only remain there for around 9 days; whereas methane remains in the atmosphere for around 12 years and CO2 even longer
Wavelength radiation
Some gases have a greenhouse effect and others do not
Because some gases can absorb short wavelength of light and re-emit them as longer wavelengths (heat)
Solar radiation spans the electromagnetic spectrum from wavelengths of 100-400 nm
Most of this is in the UV and visible part of the spectrum
The ozone later sits above our atmosphere and absorbs or reflects around 25% of this radiation (mostly UV waves)
Around 75% reach the earth’s surface and are absorbed and converted to heat
The surface of the earth re-emits this radiation as longer-wavelengths infrared waves
Without the greenhouse effect, the temperatures at the surface area of the earth would be around -18C
Longer wavelength
The majority (70-85%) of the longer-wave radiation that is re-emitted from the earth’s surface is then absorbed by gases in the atmosphere before it passes out into space
Then re-emitted back towards the earth’s surface
The continual exchange of long-wavelength radiation is what causes global warming
Greenhouse gases: atmospheric concentrations
Not all peaks in the global temperature increase correlate with a higher CO2 concentration
Other factors can influence the global temperature, including sunspot activity and variation in the earth’s orbit around the sun
Factor 1 : Climate change
A higher global average means that the total amount of water that evaporate forms oceans and lakes increases
More water in the atmosphere lead to heavier rainfall
Global warming can also have substantial effects on wind and ocean currents causing stronger hurricanes and typhoons
Factor 2 : Rising seawater
Another consequences of the increase global temperature is the rising seawater temperature and the melting effect on the polar ice caps and glaciers around the world
Factor 3 : Loss of habitat
The polar ice caps and glaciers are melting, decreasing ice habitats for some arctic organisms
When these ice caps melt, they cause a rise in sea levels, destroying coastal habitats
Factor 4 : Biotic factors
The warming of any habitat would change the species that live in the are and can cause changes to migratory patterns
Temperature species move into warmer arctic areas and compete with arctic species
Arctic species need to adapt to competition and the change in temp or emigrate to a new habitat
Change in distribution sizes and in extreme cases, the extinction of species
Changes such as these could have severe impacts on the food chains of an ecosystem disrupting the food web and having a large impact on organisms in higher trophic levels
Other effects on the biota may be an increase in decomposition due to melting permafrost, which exposes Saprotrophic bacteria to O2, releasing methane and, with an increase in temp & moisture, an increase in pest and pathogen species
Scientists and climate change
Have predicted some of these effects based on global weather models
Only partially explain all weather patterns
The changes that are occurring are often unevenly distributed
In some areas, rainfall may increase, while in others the incidence of droughts increases
Based on weather patterns and phenomena that have been observed during the last 30 years, there is little doubt that the earth’s climate is changing
Combustion of fossil fuels
In vehicles used for transport
When homes are heated
During the production of electricity
In factories powered by fossil fuels
Burning of forests for clearing
Arguments for and against
Many published findings that either rebut or support a connection between human activities and the climate change
There is little evidence to support a direct causal relationship between the correlation of global temperatures and CO2 concentrations
Cannot state with certainty that human-caused CO2 emissions are the main cause of global warming and climate change
Precautionary principle
Burden of proof
States that even without concrete evidence of causal relationship, precautionary measures should be taken to ensure that humans are not causing detrimental harm to the environment or human health
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