4.4 CLIMATE CHANGE

Greenhouse effect: Greenhouse gases absorb long-wave solar radiation in the atmosphere, increasing the overall temperature of the planet

Greenhouse gases: Gases in the atmosphere that retain heat

Greenhouse gases with the largest warming effect on Earth

• Carbon Dioxide
• Water Vapour

Greenhouse gases that have a lesser impact are

• Methane
• Nitrogen oxides [released naturally by bacteria in agriculture and vehicle exhausts]

All the Greenhouse gases make up less than 1% of the atmosphere

Greenhouse gases absorb longer wave radiation in the atmosphere

more heat is retained in the atmosphere

This impacts the global temperature and climate

The impact of a Greenhouse gas depends on

• its ability to absorb longer wave radiation
• the concentration of that gas in the atmosphere

Ability to absorb long wave radiation such as heat

Abundance [rate of release and persistance] in the atmosphere

Carbon Dioxide is very abundant within the atmosphere and persists for years

Water Vapour is released very quickly into the atmosphere but only persists for days

• Approximately 25% of solar radiation is absorbed by the atmosphere

• Approximately 75% of solar radiation penetrates the atmosphere and reaches the Earth's surface

• Earth's surface absorbs short wave energy and re-emits at longer wave lengths (as heat)

• Up to 85% of re-emmited heat is captured by greenhouse gases in the atmosphere

• Heat passes back to the surface of the Earth causing warming

If Earth had no atmosphere and therefore no greenhouse gas effect the average surface temperature would be -18 degrees celsius 

• Reduced habitat for ice-dwelling species

• Artic species are forced to migrate this causes increased competition from temperate species

• Changes in migration patterns

• Extintion of species because of inability to adapt successfully

• Changes in distribution of prey species

• The rate of Photosynthesis increases as Temperature Increases

• Increase in Transpiration as Temperature increases

• Changes in plant distribution

Global temperature and climate patterns are influenced by concentrations of greenhouse gases in the atmosphere

The is a strong dispute about whether global warming and other climate changes are due to greenhouse gas emissions from human activity

To find out Temperatures and Carbon Dixode concentrations from the past coloumns of ice have been drilled in the Anartic.

Ice deeper within is older than the ice near the surface

Bubbles of air trapped in the ice can be extracted and analysed to find the CO2 concentration

Global temperatures can be deduced from hydrogen isotopes in the water molecules

Correlations do not mean causations - research showed CO2 is a greenhouse gas

Atleast some of the tempreature variations over the years must therefore have been to rises and falls of atmospheric carbon dioxide

Evidence:

Correlation supported by ice core data over 400 000 years

Temperature shows greater variation than carbon dioxide

Most rises and falls in CO2 correlated with rises and falls in temperature

The same trend has been found in other ice cores

Strong correlation between human emissions of fossilzed organic matter and and atmospheric levels of CO2

As CO2 levels increased the amount of CO2 absorbed by carbon sinks has increased

(only about 40% of emissions have remained in the atmosphere

200 years ago both combustion of fossil fuels and CO2 concentrations have increased more steadily along with the global temperatures

CO2 concentrations and global temperature are correlated but not directly proportional as other variables also affect temperatures such as sun spot activity

Increases in greenhouse gases will likely cause

• Higher global average temperatures 
• More frequent and intense heat waves
• Areas becoming more prone to droughts
• Areas becoming more prone to intense rainfall and flooding
• Changes to ocean currents
• Tropical storms will become more frequent and more powerful

Emissions of carbon dioxide have an effect on the oceans

Over 500 billion tonnes of CO2 released by humans since the start of the Industrial Revolution have dissolved in the oceans

This has caused the pH to drop this repersents 30% acidification

Ocean acidification will become more severe if CO2 concentrations in the atmosphere continue to rise

Reef-building corals that deposit calcium carbonate in their skeletons need to absorb carbonate ions from seawater

There is a low concentration of carbonate ions in the water and the dissolved carbon dioxide makes the concentration even lower

Carbon dioxide reacts with carbonate to form carbonic acid which disassociates into hydrogen ions and hydrogen carbonate ions

Hydrogen coverts carbonate into hydrogen carbonate

Reduced carbonate concentrations in water prevent calcium carbonate from being created but the calcium carbonate within the coral reefs are dissolved

The ocean abosrbs about 25% of the CO2 emitted into the atmosphere

As atmospheric CO2 increases so do ocean levels

Since the 1800s the pH of seawater has fallen by 0.1 units this is a 30% increase in acidity

As more CO2 accumulates in the ocean, the pH of the ocean decreases

Estimates of future CO2 levels predict a further decrease of 0.5 units in pH which translates to 150% acidification

When CO2 dissolves in water it forms a variety of molecules:

Carbonic acid [affects pH]

Carbonate [releases hydrogen ions affecting pH]

Bicarbonate [releases hydrogen ions affecting pH]

Free Carbon Dioxide

Species at risk are

• Marine calcifying species [oysters, sea urchins, sea corals, calcerous plankton]

Benefit: Photysynthetic algae and sea grasses

These species need to:

• Absorb carbonate ions from seawater to make calcium carbonate in skeletons

Benefit: Low CO2 is a limiting factor for photosynthesis

Shelled organisms are very important in aquatic food chains - put the whole food chain at risk

Example: Pteropod tiny sea creatures that are a main food source for North Pacific juvinile salmon

Claims state that human activities are not the cause of Climate Change

Remeber that not all sources are trustworthy and it is important to know the motivation from both sides of the debate