Block 8: Environmental Issues and Public Health - Air Pollution Chapter 2: An Overview Of The Main Air Pollutants And Their Impacts (Continued)
Global Warming:
Carbon dioxide (CO2) and other "Climate Change" or "greenhouse" gases that contribute to Global Warming. The focus of this module is the health impacts of anthropogenic air pollutants and their impacts on human health. CO2 emissions from fossil fuel (coal, diesel, and petrol) combustion, and the resultant increase in atmospheric CO2 concentrations do not have a direct health impact. Increasing methane and ozone levels also have significant global warming impacts. The (historically) rapid increase in the average earth temperature due to the increase in these "greenhouse gas" concentrations are likely to have major large-scale impacts, including health impacts. These impacts are likely to include an increase in intense precipitation (rainfall) events, higher maximum temperatures and rising sea levels.
Anthropogenic: Originating from human activities.

Non-anthropogenic or "Natural" air pollution sources are those that do not arise from human activities.

The distinction between the two source types is not always clear-cut.

A highly simplified explanation of the mechanism of global warming 1 is illustrated in the following diagram (Figure 2.2).

The main greenhouse gases:
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
Fluorocarbons
Figure 2.2: Greenhouse gases in the atmosphere trap
heat trying to escape to space, thereby raising the
temperature of the Earth's lower atmosphere and
surface. This is the greenhouse effect.		  

Figures 2.3 and 2.4 illustrate long term CO2 trends and more recent measurements, monitored at a location that is remote from anthropogenic sources, respectively.

Figure 2-3:
Long-term trend in atmospheric CO2
concentrations (ice-core data)		 Figure 2-4:
Recent trends in atmospheric CO2
concentrations (from Christmas Island)
Source: Dave keeling and Tim Whorf (Scripps Institution of Oceanography)

A perusal of Figures 2.3 and 2.4 show that CO2 concentrations were about 280 ppm (by volume) in 1800 and have increased to about 380 ppmv. (The main GHGs are CO2, CH4 (methane), and N2O (nitrous oxide). This historically rapid increase in Greenhouse Gas (GHG) concentrations has changed the Earth’s energy balance - the GHGs trap the long wavelength radiation from the earth causing a slow increase in the average temperature.

Of the greenhouse gas emissions, CO2 emissions are by far the largest. But different gases have different Global Warming Potentials (GWP), as shown in Table 2. The Global Warming Potential is given relative to that of CO2.

Table 2: Global Warming Potentials of the Main Greenhouse Gases
Gas New GWP* Old GWP**
Carbon dioxide (CO2) 1 1
Methane (CH4) 23 21
Nitrous oxide (N2)O 296 310
HFC-23 12 000 11 700
HFC-125 3 400 2 800
HFC-134a 1 300 1 300
HFC-152a 120 140
HFC-227ea 3 500 2 900
Perfluoromethane (CF4) 5 700 6 500
Perfluoroethane (C2F6) 11 900 9 200
Sulphur hexafluoride (SF6) 22 200 23 900
* Intergovernmental Panel on Climate Change, Climate Change 2001: The Scientific Basis, Cambridge University Press, 2001, Table 3, p. 47.
** Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change, Cambridge University Press, 1995, Table 2.9, p. 121.

Trends in methane concentrations are shown in Figure 2-5:

Note that the methane concentrations are given in ppb (parts per billion). Current levels are about 1800 ppb or 1.8 ppm, compared with the CO2 concentrations of about 380 ppm. But due to the much higher GWP of methane (23), this is equivalent to a CO2 concentration of 23 x 1.8 ~ 40ppm.

REFERENCES:

  1. See, for example, http://www.cmdl.noaa.gov/climate.html.