9.2.2 Human activities which contribute to an increase in greenhouse gases in the
Human activity is raising carbon dioxide and methane
Greenhouse gas
A gas in the atmosphere that absorbs infrared radiation emitted by Earth and transfers energy to the surroundings, warming the atmosphere.
- Human activities are increasing the amounts of the greenhouse gases carbon dioxide and methane.
- More greenhouse gas means a stronger greenhouse effect and a warmer atmosphere.
The extra carbon dioxide comes mainly from fossil fuels and deforestation; the extra methane comes mainly from farming and landfill.
Where the extra carbon dioxide comes from
Fossil fuel
A finite fuel, such as coal, oil or natural gas, formed from the remains of ancient organisms over millions of years.
Deforestation
The large-scale clearing of forests, which reduces carbon dioxide removal by photosynthesis and may release stored carbon.
- Burning fossil fuels, such as coal, oil and gas, releases carbon dioxide that was locked underground.
- Deforestation removes trees that would otherwise remove carbon dioxide by photosynthesis.
- Burning or rotting the cleared trees releases even more carbon dioxide.
Where the extra methane comes from
Methane
A gas with the formula CH4\text{CH}_4CH4 that acts as a greenhouse gas and is released by sources such as cattle, flooded rice fields and landfill sites.
- Livestock such as cattle release methane as they digest their food.
- Growing rice in flooded paddy fields releases methane from the waterlogged soil.
- Rotting waste in landfill sites releases methane as it decomposes.
Judging the evidence: scale, risk and reliable sources
Peer review
The process in which independent experts in the same field examine a scientific study before it is published.
Evidence base
The collection of observations, measurements and research used to support or challenge a scientific conclusion.
- Claims about greenhouse gases should rest on a strong evidence base.
- Peer-reviewed evidence has been checked by other scientists, so it is more reliable.
- Information from non-peer-reviewed sources may be biased or incomplete.
- Media reports can distort the science through over-simplification, bias or a lack of balance.
- Judging the issue also means weighing the scale of each source and the risks involved.
- To evaluate a source, ask whether it is peer-reviewed and whether it might be biased.
- Give a named activity for each gas: fossil fuels or deforestation for carbon dioxide; cattle, rice or landfill for methane.
- Which two greenhouse gases are increased most by human activity?
- Give two human activities that increase carbon dioxide.
- Give two human activities that increase methane.
- Why is peer-reviewed evidence more reliable than a random website?
- Give two ways media reporting can distort the science.
