The Greenhouse Effect and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 269

Table 12.3. Estimated percentages of natural greenhouse effect and global warming temperature changes
due to greenhouse gases and black carbon since the mid-1800s

2010 Total
tropospheric
mixing ratio
(ppmv) or
loading (Tg)

Percentage of
current total
mixing ratio or
loading that is
anthropogenic

Percentage of
natural greenhouse
effect temperature
change (33 K) due to
component

Percentage of
global warming
temperature
change due to
component

Compound
Name Formula

<

Water vapor H 2 O(g) 10,000 1 88.9 0.5

Carbon dioxide CO 2 (g) 390 29.5 7.5 46.4

Black carbon C(s) 0.15 Tg 90 0.2 17

Methane CH 4 (g) 1.9 58 0.5 14

Ozone O 3 (g) 0.02-0.07 20-50 1.1 11

Nitrous oxide N 2 O(g) 0.325 15 1.5 4.2

Methyl chloride CH 3 Cl(g) 0.00058 < 0.1 0.3 ∼ 0

CFC-11 CFCl 3 (g) 0.00024 100 0 1.8

CFC-12 CF 2 Cl 2 (g) 0.00053 100 0 4.2

HCFC-22 CF 2 ClH(g) 0.00025 100 0 0.6

Carbon
tetrachloride

CCl 4 (g) 0.00009 100 0 0.3

CFC, chlorofluorocarbon; HCFC, hydrochlorofluorocarbon. 1 Tg = 10 6 metric tonnes = 10 6 g.

Sources: Derived from Jacobson (2010b) and IPCC (2007).

Whereas greenhouse gases transmit solar radiation
and absorb thermal-IR radiation, BC strongly absorbs
all wavelengths of solar radiation, and BrC strongly
absorbs UV and short visible wavelengths of solar radi-
ation. BC and BrC both weakly absorb thermal-IR radi-
ation. Thus, greenhouse gases and BC/BrC both warm
the air, but by different mechanisms.
Table 12.3 shows that the most important natural
greenhouse gas is water vapor ,which accounts for
approximately 29.4 K (89 percent) of the 33 K tem-
perature increase resulting from natural greenhouse
warming. Carbon dioxide is the second most impor-
tant and abundant natural greenhouse gas, accounting
for about 7.5 percent of the natural greenhouse effect.
Black carbon, whose major natural source is forest
fires, is estimated to be responsible for only 0.2 percent
of the Earth's natural warming above its equilibrium
temperature.
Figure 12.4 gives the percentage absorption of inci-
dent thermal-IR radiation by different greenhouse gases
versus wavelength. Water vapor is a strong absorber
at several wavelengths between 0.7

atmospheric window, gases are relatively transparent
to the Earth's outgoing thermal-IR radiation, allow-
ing the radiation to escape to space. Of the natural
gases in the Earth's atmosphere, ozone and methyl chlo-
ride absorb radiation within the atmospheric window.

m and 8 m

and above 12 m. Carbon dioxide absorbs strongly at

2.7 and 4.3 m and above 13 m. Little thermal-IR

Figure 12.4. Percentage absorption of radiation by
greenhouse gases at infrared wavelengths. Adapted
from Valley (1965).

absorption occurs between 8 m. This wave-

length region is called the atmospheric window .Inthe

m and 12