The earth’s climate

The energy from the sun passes through the atmosphere and is absorbed by the land and sea. This energy is then reflected back from the Earth’s surface and some of this is trapped by gases near the earth’s surface, keeping it warm. They work in the same way as glass in a greenhouse, hence they are termed greenhouse gases (GHGs). The main GHGs are:

  • Water vapor (H2O)
  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrous oxide (N2O)
  • Ozone (O3)
  • CFCs

Without this layer of greenhouse gases, the earth’s temperature would be permanently close to freezing.

The earth has experienced a relatively constant level of greenhouse gases over its recent history, through a natural cycle where the amount of emissions into the atmosphere is balanced by the natural degradation of GHGs and absorption of carbon dioxide by plants.

However, we have upset this balance in a number of ways:

Deforestation – by destroying forests we have reduced the amount of CO2 that they can absorb, leading to increased amounts of CO2 in the atmosphere.

Burning fossil fuels – by burning coal, oil and gas, we have released large quantities of GHGs that have been trapped underground for millions of years, releasing them much more quickly than if they had been left to decay naturally.

Population growth – population growth has resulted in increased livestock and agricultural production which both contribute significantly to GHG emissions.

The graph shows the sharp increase in GHG concentration in the atmosphere:

 

The latest report from the IPCC (Intergovernmental Panel on Climate Change) in 2013 concludes that human influence on the climate system is clear, with human activities extremely likely to have been the dominant cause of the observed warming since the mid-20th century.

It’s getting warmer….?

Scientists confirm that each of the past three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850, with concentrations of CO2 increasing by 40% since pre-industrial times, primarily from fossil fuel emissions.

Governments have pledged to limit temperature rise to 2°C to avoid potentially dangerous consequences, however scientists believe that without immediate reductions in greenhouse gas emissions, the world will not be able to meet this target and we are more likely to see a rise of 3°C–5°C.

But, remember that this is a global temperature rise. The term ‘global warming’ can be misleading because not everywhere will see a rise. In the UK we are more likely to experience hotter, drier summers, wetter winters, and an increased risk of flash flooding.

The global temperature increase will also result in a sea level rise due to melting ice, and will put many of the world’s species at risk.

 

 

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