CAUSES OF CLIMATE CHANGE: Anthropogenic

• Burning of fossil fuels: People drive cars. Heat and cool their houses. People cook food. All those activities take energy.

• In its 5th Assessment Report, the Intergovernmental Panel on Climate Change, a group of 1,300 independent scientific experts from countries all over the world under the auspices of the United Nations, concluded that there’s a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane, and nitrous oxide have caused much of the observed increase in Earth’s temperatures over the past 50 years.
• Other causes: Deforestation, changes in land use, soil erosion and agriculture (including livestock), the Industrial revolution, and Mining and Quarrying.

Climate Forcing:

• There are a number of natural mechanisms that can upset the global energy balance, for example, fluctuations in the Earth’s orbit, variations in ocean circulation, and changes in the composition of the Earth’s atmosphere.
• By altering the global energy balance, such mechanisms “force” the climate to change. Consequently, scientists call them “climate forcing” mechanisms.
• Climate ‘forcing’ are factors in the climate that either increase or decrease the effects to the climate system.
• Positive ‘forcing’ such as greenhouse gases warm the earth while the negative ‘forcing’such as the volcanic eruptions, etc. cools the earth system.
• Examples of forcing include:
  1. Surface reflectivity (albedo)
  2. Human induced changes in greenhouse gases
  3. Atmospheric aerosols (volcanic sulfates, industrial output)
• These examples influence the balance of energy entering and leaving the Earth system.