Anthropogenic activities sources

Concerns over atmospheric methane as a greenhouse gas and the large contribution of biomethanogenesis as a source of this gas make it important to determine the relative significance of various components of this activity. A recent paper (8) summarized estimates (28-30) of source fluxes of atmospheric methane based on several carbon isotopic studies and presented new data on natural sources and biomass burning. These data (Table III) show that of a total flux of 594 million tons (Tg) per year, 83% is produced via biomethanogenesis from a combination of natural (42%) and anthropogenic (41%) sources. 

Due to the imbalance of sources and sinks, atmospheric N2O is increasing by 3 Tg N/yr or 0.2%/yr. Figure 12-9 shows average N2O mixing ratios from four stations in the NOAA-CMDL network, Barrow, Mauna Loa, Samoa, and the South Pole (data are from the NOAA-CMDL and can be obtained from www.cmdl.noaa.gov). The most recent IPCC estimate gives a total N2O source of 16 Tg N, 7 Tg of which are a result of human activities (IPCC, 1997). The largest contribution to the anthropogenic N2O sources is 3 Tg N from... 

Nuclear explosions and nuclear power production are the major sources of anthropogenic activity in the environment. But radionuclide use in medicine, industry, agriculture, education, and production and transport, use, and disposal from these activities present opportunities for wastes to enter the environment (Whicker and Schultz 1982a Table 32.6). Radiation was used as early as... 

In short, the combination of absorption and scattering of light by mineral dusts, combined with an increase in these due to anthropogenic activities, has the potential to contribute to climate change. However, many uncertainties need to be removed before these effects can be confidently quantified. For example, the infrared absorption depends on the composition of the dust and as seen in Fig. 14.35, this can be quite variable from location to location and even as a function of time from one source. This one effect alone can lead to a large variability in the predicted effects on radiative forcing (Sokolik et al., 1998). 

These substances enter the marine environment from a variety of sources, both through natural phenomena and anthropogenic activities. In 1985, the National Academy of Sciences (NAS) published an assessment of petroleum pollution of the world s oceans and estimated that between 1.7 and 8.8 million metric tons per annum (mta) of oil enter the oceans. Within this range, 3.2 mta is regarded as the best single estimate—equivalent to about 0.1% of the total oil produced annually worldwide (about 3 billion metric tons). 

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