The causes of climate change

• Not all areas of the world are warming at the same rate: rates vary between the two hemispheres
• Some areas of the world have not warmed at all in recent decades, whilst others have 
• Industrial areas are not warming as fast as more remote areas
• The 3 warmest years on record have occured since 1998

The natural greenhouse effect

• The driving force for weather and climate is the sun and its radiation
• The earth's atmosphere reflects back 30% of the suns radiation back into space
• Some radiation is absorbed by the Earth's surface and some is re-emitted by gases known as greenhouse gases, which warm the Earth's atmosphere by 33 degrees Celcius - this is the greenhouse effect 

Carbon dioxide

• Although onlly makin g up 0.04% of the Earth's atmosphere, CO2 is a major greenhouse gas
• It is given off when carbon-based fuels are burned, e.g. coal and oilhave increased atmospheric CO2 by 25%

Chlorofluorocarbons (CFC's)

• First used in the 1960's as propellants in spray cans, foam plastics, and refrigerant fluids
• They absorb solar radiation and contribute to global warming
• It thins the ozone layer 

Methane

• A minor gas but very effective in retaining heat, it has been increasing as CO2 has been increasing
• Causes include rice production, burning vegeitation, coal mining and livestock

The enhanced greenhouse effect is the increase in the natural greenhouse effect, said to be caused by human activities which increase the quantity of greenhouse gases in the atmosphere

It is caused by the burning of fossil fuels and deforestation and the release of natural stores of nitrogen and carbon dioxide - all influence by human activity

As global temperatures increase so does the main greenhouse gas - water vapour. Increasing global temperatures lead to greater evapouration of water, which then leads to greater condensation. This causes increased cloud cover, which traps hheat in the atmosphere

Global warming is part of a natural cycle of climate change which has taken place over the last 18,000 years. The Earth has fluctuated between cold glacial periods and wamer periods. Possible explanations for why this happens are changes in solar output, variations in the Earth's orbit, cosmic collision and volcanic emissions 

Changes in solar output 

• Sunspots (increased activity on the surface of the sun, that radiates more heat) work in cycles and the sun's energy varies over short periods. Although they do not play a major part in global warming it can affect the global temperatures

Variations in the Earth's orbit

• The Milankovich Cycles state that the Earth's orbit varies every 100,000 years, with changes every 41,000 years. It has three main movements that effect global temperatures. The first is that the Earth's orbit around the sun changes from circular to elliptical meaning at certain points the Earth is closer to the sun meaning it recieves more radiation 
• Another movement is that the Earth's atmosphere tips towards the sun between 21 degrees to 25 degrees. Similar to this is the last movement where the earth wobbles on its axis so when it does this it recieves more radiation 

Cosmic collision and volcanic emissions

• Volcanic emissions can have an impact on the global climate. The eruptions of Mt Pinatubo in 1991 released huge quantities of ash that blocked out the sunlight and increased clouod cover that kept in more radiation
• This is simalirly the case when a comit hits the earth, the ash created does the same thing as the volcanic ash