Any external factor that originates from outside the climate system and can become a cause of climate change is called Climate Forcing. These factors are specifically known as forcings because they drive the climate to change. There are natural forcings and man-made forcings. For examples:

• Surface reflectivity (Albedo).
  
  
• Human-caused, or anthropogenic climate  forcing include emissions of heat-trapping gases (also known as greenhouse gases) and changes in land use that make land reflect more or less sunlight energy. 
  
  
• Atmospheric aerosols due to human activity or volcanic eruption etc. that put light-reflecting particles into the upper atmosphere.
  
  

The peculiar feature of all climate forcing is that they influence the balance of the energy entering and leaving the Earth system i.e, the amount of energy we receive from the sun, and the amount of energy we radiate back into space.  Climate change refers to the change of climate that alters the composition of the global atmosphere. It is usually measured in major shifts in temperature, rainfall, snow, and wind patterns lasting decades or more.

The causes of climate change can be classified into two types; natural and anthropogenic.

Natural causes:

• Solar Irradiance: The change in energy output of the sun brings changes in climate. Solar output varies according to the 11 year solar cycle.
  
  
• Volcanic Eruptions: When volcanoes erupt, thousands of tons of sulfur dioxide is released into the atmosphere which cause cooling and warming of the earth respectively.
  
  
• Plate tectonics: Tectonic plates rearrange the topography of the earth which  brings changes in the circulation of oceans and subsequently changes the patterns of the global climate.  
  
  
• Variations in the Earth’s Orbit: Variations in the orbit of the planet bring changes in seasonal and geographical distribution of the light from the sun that affects the global climate.
  
  

Anthropogenic causes:

• Emission of Greenhouse Gases: Release of greenhouse gases like Carbon dioxide is one of the main reasons for climate change.  For example, human activities such as deforestation, burning of fossil fuels, surface mining, agriculture, emissions from industries etc. are also releasing other greenhouse gases into the atmosphere.
  
  
• Land Use Change: Climate change is also assisted by changes in land use and land cover that are caused because of human activities such as agriculture.
  
  

Many of these factors are interrelated, and atmospheric, ocean and land interactions can involve complex feedback mechanisms can either enhance or dampen changes to the climate system.