Last edited 27 Apr 2018

Greenhouse gases


[edit] Introduction

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:

Ozone and chlorofluorocarbons (CFCs) are also greenhouse gases.

The main constituents of the atmosphere; nitrogen, oxygen and argon, are not greenhouse gases.

[edit] 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.

[edit] 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.
  • Deforestation.
  • 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.

[edit] Legislation and policy

The establishment of the Climate Change Act 2008 committed the UK to reducing greenhouse gases by at least 80% by 2050 (from the 1990 baseline).

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:

[edit] Setting national policy and strategy

[edit] Reducing energy demand and helping people to use energy efficiently

[edit] Investing in low carbon technologies

[edit] Public reporting

Ref Department of Energy and Climate Change (DECC), 2014.

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.

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