Greenhouse gases are relatively transparent to short-wave infrared radiation (such as heat from the sun). This means that they allow sunlight to enter the atmosphere and heat the Earth’s surface. These surfaces then re-radiate that heat as long-wave infrared radiation, which greenhouse gases tend to absorb rather than transmit. The result is that the long-wave infrared radiation is ‘trapped’ and heat accumulates in the atmosphere causing a warming process. This process is known as the ‘greenhouse’ effect because it is similar to the effect that glass has, trapping heat in greenhouses.
The four main greenhouse gases are:
- Water vapour.
- Carbon dioxide.
- Nitrous oxide.
Ozone and chlorofluorocarbons (CFCs) are also greenhouse gases.
The main constituents of the atmosphere; nitrogen, oxygen and argon, are not greenhouse gases.
 Gas concentrations in the atmosphere
Greenhouse gases are necessary in the atmosphere to maintain a stable temperature for life to exist and it is usual for the gas concentrations to fluctuate. These changes are generally slow, with average global air temperature varying over a period of hundreds of thousands or millions of years, and this slow rate of change allows life on earth to adapt. However, over the last 150 years the rate of increase has been significantly higher than normal, resulting in a relatively fast increase in average global air temperatures.
The concentrations of greenhouse gases in the atmosphere are the result of the balance between sources (human activities and natural systems) and sinks (removal of the gas from the atmosphere through natural processes or negative emissions such as carbon capture), ref Intergovernmental Panel on Climate Change (IPCC) 2013.
Measurements of atmospheric carbon dioxide began in 1958 and these have revealed the full impact of human activities from the natural annual cycle of the biosphere. Since 1970, increased concentrations of methane and nitrous oxide have also been detected. Between 1999 and 2006, the levels of methane stabilised, but increases were detected again in 2007. The increase in greenhouse gases is a key indicator of global climate change.
 Sources of greenhouse gases from human activity (anthropogenic)
There are a number of human activities that result in increases in greenhouse gases in the atmosphere, including:
- Burning fossil fuels.
- Livestock enteric fermentation.
- Paddy fields and land use changes.
- Use of chlorofluorocarbons (CFCs).
- Agricultural activities, including the use of fertilizers.
It is considered likely that the increased atmospheric concentrations of greenhouse gases from human activities and the resulting warming will have a wide range of effects including; an increase in extreme weather events, sea level rise, loss of biodiversity and variation in agricultural productivity.
 Legislation and policy
The Committee on Climate Change was formed following the 2008 act to assess how the UK could help meet the reduction targets. It proposed that the reduction will be achieved through a suite of methods:
 Setting national policy and strategy
- Setting carbon budgets for limiting UK greenhouse gas emissions.
- Undertaking further research to inform climate change policy.
- Using the EU Emissions Trading Scheme to help deliver reductions.
- Ensuring project and policy appraisals calculate accurate carbon amounts.
 Reducing energy demand and helping people to use energy efficiently
- Reducing energy demand with meters and other energy efficient measures.
- Reducing emissions by improving energy efficiency of properties through the Green Deal.
- Providing incentives for organisations to take up energy-efficient technologies and practices through the government Carbon Reduction Commitment Energy Efficiency Scheme.
- Reducing emissions from transport and agriculture.
 Investing in low carbon technologies
- Creating an industry for carbon capture and storage.
- Reforming the UK’s electricity market.
- Provision of over £200 million for innovation in low carbon technology.
 Public reporting
- Measuring and reporting environmental impacts (Defra, 2013).
- Asking local authorities to measure and report their greenhouse gas emissions.
NB On 15 October 2016 it was announced that 170 countries in Kigali, Rwanda, had agreed that all HFC’s should be phased out through an amendment to the Montreal Protocol. See HFC phase out for more information.
 Related articles on Designing Buildings Wiki
- Air conditioning inspection.
- Biodiversity offsetting.
- Carbon Reduction Commitment Energy Efficiency Scheme.
- Climate change act.
- Climate change science.
- Construction 2025.
- Green deal.
- HFC phase out.
- Ozone depleting substances.
- Refrigerant selection.
- Renewable energy.
- R22 phase out.
- Smart cities.
- UK Climate Change Risk Assessment.
 External references
- Carbon Plan.
- Carbon Reduction Commitment Energy Efficiency Scheme.
- Climate Change Act 2008.
- Climate Change 2013, The Physical Science Basis (Intergovernmental Panel on Climate Change, 2013).
- Environmental Reporting Guidelines: Including mandatory greenhouse gas emissions reporting guidance (Defra, 2013).
- Green Deal
- Reducing the UK’s greenhouse gas emissions by 80% by 2050 (DECC, 2014).
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