4.4 ~ Climate change

Greenhouse 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