Introduction to Climate Change

4. Causes of Climate Change

To design a set of policy responses to minimize the impacts of climate change requires an understanding of the major causes of that change.

A. GHG Emissions

The primary cause of climate change, of course, is the increased emissions of greenhouse gases from fossil fuel burning and other industrial processes. Each of the major greenhouse gases has different sources. Carbon dioxide, comprising nearly 50% of all anthropogenic greenhouse gases is by far the most important. Eighty percent of all carbon dioxide is emitted by fossil fuel burning, in everything from large power plants to automobiles.

Methane is produced by waste decomposition, the decay of plants and from certain agricultural practices such as cattle production and the flooding of fields to grow rice. Nitrous oxides are typically produced from automobile exhaust and other industrial processes. Chlorofluorocarbons (CFCs) were used in refrigerants, air conditioners and other products, until their phase out under the Montreal Protocol regime, discussed supra. Unfortunately, among the most potent greenhouse gases are the common alternatives to CFCs, including hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6), all of which are now covered by the Kyoto Protocol.

Most greenhouse gas emissions come from industrial activity and thus, not surprisingly, the United States and other industrialized countries are the primary contributors to the increase in atmospheric concentrations of greenhouse gases over the past century. The United State is also the world's leader in current emissions as well. With only 4% of the world's population, we now emit an estimated 25% of the world's greenhouse gases each year.

B. Carbon Reservoirs and Sinks

Many forestry, land use and agricultural practices are eliminating important natural sinks and reservoirs for atmospheric carbons. "Carbon sinks" refer to processes that remove a net amount of carbon from the atmosphere (e.g. photosynthesis). Thus, carbon sinks present important opportunities for reducing the overall increase in atmospheric concentrations of greenhouse gases. "Carbon reservoirs" currently store carbon previously removed from the atmosphere. Carbon reservoirs are in equilibrium with the atmosphere unless disturbed, in which case they can release carbon and add to the concentrations of greenhouse gases in the atmosphere. Forests are perhaps the most well known carbon reservoirs and sinks.