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C9 B) Greenhouse Gases & Climate Change
C9 B) Greenhouse Gases & Climate Change
We have been monitoring global temperatures using thermometers for the last 150 years. Over the last 100 years, the average global temperature has increased by 0.9°C and the increase in temperature in the UK has been 1°C.
Scientists have also been able to use ice cores to see what the proportion of certain gases were in the atmosphere over the last few thousand years. Ice cores are cylinders of ice drilled out of a glacier or ice sheet. When the ice sheets or glaciers freeze, the ice encloses small bubbles of air (gas). We can use these trapped bubbles of gas to measure the concentrations of gases that were present in the atmosphere at the time that this part of the ice was frozen. We are interested in the greenhouse gases that lead to the enhanced greenhouse effect which causes temperatures on earth to rise. The greenhouse gases are water vapour, carbon dioxide, nitrous oxide, methane and CFCs. There has always been a certain quantity of these greenhouse gases (except CFCs, which are man-made) in the atmosphere but the quantities of these gases in the atmosphere have increased significantly in the last few centenaries. Greenhouse gases have increased because of the following reasons:
Scientists have also been able to use ice cores to see what the proportion of certain gases were in the atmosphere over the last few thousand years. Ice cores are cylinders of ice drilled out of a glacier or ice sheet. When the ice sheets or glaciers freeze, the ice encloses small bubbles of air (gas). We can use these trapped bubbles of gas to measure the concentrations of gases that were present in the atmosphere at the time that this part of the ice was frozen. We are interested in the greenhouse gases that lead to the enhanced greenhouse effect which causes temperatures on earth to rise. The greenhouse gases are water vapour, carbon dioxide, nitrous oxide, methane and CFCs. There has always been a certain quantity of these greenhouse gases (except CFCs, which are man-made) in the atmosphere but the quantities of these gases in the atmosphere have increased significantly in the last few centenaries. Greenhouse gases have increased because of the following reasons:
- Burning of fossil fuels – the fossil fuels are oil, coal and natural gas. The burning of fossil fuels results in carbon dioxide being released into the atmosphere. We burn fossil fuels to heat homes and for transport (car, lorries, aeroplanes etc)
- Farming – the farming process emits carbon dioxide at every stage of production because each stage requires energy (some of the stages of production are storage, processing, packaging, transportation, preparation and serving). Furthermore, the rearing of livestock, especially cattle, results in large quantities of methane, carbon dioxide and nitrous oxide being emitted into the atmosphere.
- Deforestation – forests play a significant role in the carbon cycle. Whilst trees and plants grow, they photosynthesise and absorb carbon dioxide from the atmosphere; they store the absorbed carbon dioxide as carbon compounds in the plant. When we cut forests down, carbon dioxide absorption stops as the trees are dead. Also, the carbon that the tree has stored will be released into the atmosphere when the trees/ vegetation is being burnt or if the tree/ vegetation is being left to rot.
The graphs below show how the levels of carbon dioxide in the atmosphere and global temperatures have changed over the last century.
The increase in the concentration of greenhouse gases leads to the enhanced greenhouse effect. It is known as the enhanced greenhouse effect because the greenhouse effect would naturally occur as the atmosphere already has a certain quantity of these greenhouse gases. If the greenhouse effect didn’t exist, the average global temperature on earth would be -18°C, which is significantly lower than the average global temperature now (16°C); if we didn’t have the greenhouse effect, earth would be too cold to support life. However, recently the concentration of greenhouse gases has increased which means that we are getting a greater greenhouse effect than usual; this is why it is known as the enhanced greenhouse effect. The enhanced greenhouse effect is resulting in average global temperatures rising.
How does the greenhouse effect work?
The sun emits short-wave infrared radiation. Infrared waves are part of the electromagnetic spectrum. The short-wave infrared radiation passes through the earth’s atmosphere and hits the earth. Some of the energy that hits the earth is absorbed and the rest is re-emitted as longer wave infrared radiation. Some of the longer wave infrared radiation passes through the atmosphere into space and some is absorbed by the greenhouse gases. The greenhouse gases that absorbed the long wave infrared radiation heat up and reradiate this thermal energy in all directions including back down towards earth, which heats the earth – this is the greenhouse effect.
As there are more greenhouse gases in the atmosphere, more of the long wave infrared radiation that is being re-emitted from the earth is being absorbed and radiated back down to earth by the greenhouse gases. This results in the temperature of earth rising, which is the enhanced greenhouse effect.
The sun emits short-wave infrared radiation. Infrared waves are part of the electromagnetic spectrum. The short-wave infrared radiation passes through the earth’s atmosphere and hits the earth. Some of the energy that hits the earth is absorbed and the rest is re-emitted as longer wave infrared radiation. Some of the longer wave infrared radiation passes through the atmosphere into space and some is absorbed by the greenhouse gases. The greenhouse gases that absorbed the long wave infrared radiation heat up and reradiate this thermal energy in all directions including back down towards earth, which heats the earth – this is the greenhouse effect.
As there are more greenhouse gases in the atmosphere, more of the long wave infrared radiation that is being re-emitted from the earth is being absorbed and radiated back down to earth by the greenhouse gases. This results in the temperature of earth rising, which is the enhanced greenhouse effect.
The Effects of Climate Change
The effects of climate change vary considerably:
The effects of climate change vary considerably:
- Rising temperatures and a reduction in rainfall in some areas will result in some areas becoming deserts (desertification). This may mean that farmers will be unable to grow crops, which could lead to famine and malnutrition. Also, the drought will become more frequent and more severe
- Sea levels will rise resulting in some areas that are low lying becoming submerged under the sea (flooding). Deltas are especially at risk e.g. Bangladesh.
- Climate change is changing the locations where animals can live because the place where they currently live is becoming too hot, doesn’t have enough rainfall, is lost to rising sea levels etc. If the animals are unable to survive in their new location or unable to move, they may become an endangered species or become extinct.
- The frequency and severity of tropical storms may increase. Also, the areas that may be at risk of tropical storms may also increase as sea and atmospheric temperatures rise.
- The ice caps will melt
- Climate change may affect the migration patterns of some birds because temperatures have changed. Birds migrate to warmer regions during winter and cooler regions during summer.
- Overall, climate change will reduce biodiversity because certain species may be unable to survive and become extinct.
The Evidence
The temperature on earth has changed a considerable amount over time. Also, the climate of earth is an extremely complex system. Both of these factors mean that we cannot say for certain why temperatures on earth are changing. However, there is lots of evidence to support the theory that increasing greenhouse gases are responsible for climate change. The reports that scientists have made investigating climate change have all been peer-reviewed, which has led to a general consensus in the scientific community that increases in greenhouse gases are responsible for climate change. However, some businesses, individuals in society and parts of the media do not believe climate change is being caused by the increase in greenhouse gases.
The temperature on earth has changed a considerable amount over time. Also, the climate of earth is an extremely complex system. Both of these factors mean that we cannot say for certain why temperatures on earth are changing. However, there is lots of evidence to support the theory that increasing greenhouse gases are responsible for climate change. The reports that scientists have made investigating climate change have all been peer-reviewed, which has led to a general consensus in the scientific community that increases in greenhouse gases are responsible for climate change. However, some businesses, individuals in society and parts of the media do not believe climate change is being caused by the increase in greenhouse gases.