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

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Removed from atmosphere:

* Photosynthesis
* Dissolving into the oceans

H2O vapour

Released in the atmosphere:

* Evaporation from oceans
* Transpiration in plants

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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