Causes of climate change

A natural function of the Earth's atmosphere is to keep in some of the heat that is lost from the Earth. This is known as the greenhouse effect.

  1. The atmosphere allows the heat from the Sun (short-wave radiation) to pass through to heat the Earth's surface.
  2. The Earth's surface then gives off heat (long-wave radiation).
  3. This heat is trapped by greenhouse gases (eg methane, carbon dioxide and nitrous oxide), which radiate the heat back towards Earth.
  4. This process heats up the Earth.
The Earth absorbs and reflects solar radiation. Greenhouse gases trap heat and warm the Earth. Some radiation is reflected away from the Earth. Pollution adds to greenhouse gases.

Human factors increasing global warming

Some human activities increase the greenhouse gases in the atmosphere:

  • Burning fossil fuels, eg coal, gas and oil - these release carbon dioxide into the atmosphere.
  • Deforestation - trees absorb carbon dioxide during photosynthesis. If they are cut down, there will be higher amounts of carbon dioxide in the atmosphere.
  • Dumping waste in landfill - when the waste decomposes it produces methane.
  • Agriculture - agricultural practices lead to the release of nitrogen oxides into the atmosphere.
The carbon cycle and the effects of humans.

When humans burn fossil fuels, the natural concentration of CO2 changes. Carbon moves through the environment in a cycle, never lost nor gained, but flows from one store to another.

Natural factors increasing global warming

There are also natural factors which contribute to increased global warming:

  • Orbital changes - the Earth has natural warming and cooling periods caused by Milankovitch cycles or variations in the tilt and/or orbit of the Earth around the Sun (Wobble, roll and stretch theory).
  • Solar output - there can be fluctuations in the amount of radiation from the Sun. If there is a high amount emitted, there will be an increase in Earth's temperatures.
  • Volcanic activity - during a volcanic eruption carbon dioxide is released into the atmosphere, this can also affect sea-ice and ocean currents. During a period known as the ‘Little Ice Age’ temperatures around the UK and across north-east Europe plunged to three degrees lower than normal. This led to the River Thames in London freezing solid in the winter months. In other parts of the world, glaciers advanced and plants were destroyed by the freezing conditions.
Frost fairs took place on the River Thames during a period of extremely cold climate called the Little Ice Age.
A frozen River Thames due to volcanic activity