GEOG 438W
Human Dimensions of Global Warming

Proximate Causes

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The Human Activities That Cause Climate Change

Human activities are releasing huge quantities of GHGs to the atmosphere, trapping more of the longwave radiation for longer periods and forcing the surface temperature to rise. These activities release many GHGs and indirectly influence the concentrations of many others, but the ones most responsible for warming are three naturally occurring gases, and a group of man-made chemicals. The natural gases are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The manufactured chemicals are collectively called the halocarbons and include chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and others. Focusing on the portion of warming caused by the natural gases released by human activity, carbon dioxide is responsible for 72 percent of the warming, methane for 18 percent, and nitrous oxide for 9 percent.

Pie charts showing greenhouse gases by sector & also by CO2, CH4, and N2O. See text version below.
Figure 2.3: Annual greenhouse gas emissions by sector.
Click here for a text description of figure 2.3
Annual Greenhouse Gas Emissions by Sector
Process Percentage of gas emitted
Industrial processes 16.8%
Power stations 21.3%
Waste disposal and treatment 3.4%
Land use and biomass burning 10.0%
Residential, commercial, and other sources 10.3%
Fossil fuel retrieval, processing, and distribution 11.3%
Agricultural byproducts 12.5%
Transportation fuels 14.0%

 

Carbon Dioxide (72% of total)
Process Percentage of gas emitted
Industrial processes 20.6%
Power stations 29.5%
Fossil fuel retrieval, processing, and distribution 8.4%
Land use and biomass burning 9.1%
Residential, commercial, and other uses 12.9%
Transportation fuels 19.2%

 

Methane (18% of total)
Process Percentage of gas emitted
Agricultural byproducts 40.0%
Residential, commercial, and other uses 4.8%
Land use and biomass burning 6.6%
Waste disposal and treatment 18.1%
Fossil fuel retrieval, processing, and distribution 29.6%<
Industrial processes 0.9%

 

Nitrous Oxide (9% of total)
Process Percentage of gas emitted
Agricultural byproducts 62.0%
Power stations 1.1%
Land use and biomass burning 26.0%
Industrial processes 5.9%
Waste disposal and treatment 2.3%
Residential, commercial, and other uses 1.5%
Transportation fuels 1.2%