The Carbon Quandary: Essential and Detrimental - Sustainable Design: The Science of Sustainability and Green Engineering - page 276

Table 7.4 Level of Scientific Understanding (LOSU) of Radiative Forcings

Forcing Phenomenon LOSU

Well-mixed greenhouse gases High

Stratospheric O 3 Medium

Tropospheric O 3 Medium

Direct sulfate aerosols Low

Direct biomass-burning aerosols Very low

Direct fossil-fuel aerosols (black carbon) Very low

Direct fossil-fuel aerosols (organic carbon) Very low

Direct mineral dust aerosols Very low

Indirect aerosol effect Very low

Contrails Very low

Aviation-induced cirrus Very low

Land use (albedo) Very low

Solar Very low

Source: Intergovernmental Panel on climate change, Climate Change 2001: The
Scientific Basis , Chapter 6, IPCC, Geneva, Switzerland, 2001.

hydroxyl radical (OH):

Water Vapor
↓

+ + → + . + +

CH 4 OH 9O 2 CO 2 0 5H 2 2H 2 O 5O 3

↓ ↓

CarbonDioxide Ozone

This indicates that the reaction creates carbon dioxide, water vapor, and ozone,
all of which are greenhouse gases, so the effect of one molecule of methane is
devastating in its production of gases that contribute to the greenhouse effect.
Halocarbons, the chemical class linked to the destruction of stratospheric
ozone, are also radiant gases. The most effective global-warming gases are CFC-
11 and CFC-12, both of which are no longer manufactured, and the banning of
these substances has shown a leveling off in the stratosphere. Nitrous oxide is also
in the atmosphere mostly as a result of human activities, especially the cutting
and clearing of tropical forests. The greatest problem with nitrous oxide is that
there appear to be no natural removal processes for this gas, so its residence time
in the stratosphere is quite long.
The net effect of these global pollutants is still being debated. Various atmo-
spheric models used to predict temperature change over the next hundred years
vary widely. They nevertheless agree that some warnings will occur even if we
do something drastic today. By the year 2100, even if we do not increase our
production of greenhouse gases and if the United States takes actions similar
to those of the Kyoto Accord, which encourages a reduction in greenhouse gas
production, the global temperature is likely to be between 0.5 and 1.5 ◦ C warmer.