The Greenhouse Effect and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 274

12.3. Recent and Historical
Temperature Trends
To assess the extent and seriousness of global warm-
ing today, it is necessary to investigate the temperature
record of past climates on the Earth. In the following
subsections, recent and historic changes in global tem-
perature are examined.

Biomass burning

T o tal

Coal minin g

100

R i c e fa r m i ng

Livestock

10

Landfills

12.3.1. Recent Temperature Record
Three types of datasets are used to assess global and
regional air temperature changes during the past cen-
tury. All three show evidence of near-surface global
warming.
The first type of dataset is one that uses temperature
measurements taken between 2 m and 10 m above the
surface at land-based meteorological stations and fixed-
position weather ships. Two worldwide datasets using
such measurements include the U.S. Global Historical
Climate Network (GHCN) dataset (Peterson and Vose,
1997) and the UK Meteorological Office dataset (Bro-
han et al., 2006). Both datasets include measurements
since the 1850s. The number of measurement stations
included in each dataset changes yearly. The GHCN
dataset includes data from fewer than 500 stations prior
to 1880, a high of 5,464 stations in 1966, and about
2,000 stations more recently. The Brohan et al. (2006)
dataset includes data from fewer than 250 stations prior
to 1880, up to 1,800 stations in the 1950s, and fewer
than 1,000 stations more recently.
Figure 12.13 shows changes in globally averaged
near-surface air temperatures between 1880 and 2010
from the GHCN dataset. Temperatures were relatively
stable between 1860 and 1910, but steadily increased
from 1910 to 1940. Temperatures were stable or slightly
decreased between 1940 and the mid-1970s, but they
increased rapidly from the mid-1970s to 2010. Nine
of the ten warmest years were in the 2000s, and the
years 2010 and 2005 were tied for the warmest years on
record. The data indicate that the average global near-
surface air temperature has warmed by 0.7 ◦ Cto0.9 ◦ C
since 1880.
Asecond type of dataset is one that uses tempera-
ture measurements at different altitudes taken from bal-
loons (radiosondes) twice daily at about 1,000 locations
over land worldwide. Figure 12.14 shows the vertical
change in the globally averaged temperature between
1958 and 2007 from the dataset. It indicates that tem-
peratures in the troposphere (pressures greater than 200
hPa) increased and temperatures in the stratosphere
(pressures less than 200 hPa) decreased during this

Gas supply

Gas flaring

1

1860 1880 1900 1920 1940 1960 1980 2000

Year

Figure 12.11. Global anthropogenic emissions of
methane from different sources from 1860 to 1994.
1Tg = 10 6 metric tonnes = 10 12 g. Data from Stern

and Kaufman (1998).

Anthropogenic emissions of N 2 O(g) also increased
in the nineteenth and twentieth centuries. Nitrous oxide
is emitted mostly by bacteria in fertilizers and sewage,
as a combustion product during biofuel, biomass, and
fossil fuel burning, and as a result of nylon production.
In the 1930s and 1940s, CFCs and HCFCs, syn-
thetic long-lived chlorinated compounds, were devel-
oped for industrial uses (Chapter 11). These compounds
contribute to both stratospheric ozone destruction and
global warming because many absorb thermal-IR radi-
ation within the atmospheric window. Whereas strato-
spheric mixing ratios of CFC-11 and -12 and CCl 4 (g)
are leveling off or decreasing, those of HCFC-22,
other HCFCs, and HFCs are increasing (Figure 11.21).
HFCs and other fluorine-containing compounds, such
as sulfur hexafluoride [SF 6 (g)] and perfluoroethane
[C 2 F 6 (g)], are strong absorbers in the atmospheric win-
dow; thus, their buildup is a cause for concern. Table
11.2 provides the global warming potential of CFCs,
HCFCs, and HFCs.
Figures 12.12a and 12.12b show changes in the
global emissions of black carbon by country and sector
from 1850 to 2005. Black carbon emissions increased
worldwide during this period, although its emissions
in the United States and Europe first increased and
then decreased. Emissions of sulfur dioxide, a pre-
cursor to particulate sulfate aerosol, a cooling agent,
have remained relatively steady between 1970 and 2005
(Figure 12.12c). The increase in global BC emissions
and relatively constant sulfur dioxide emissions imply
a net warming due to anthropogenic aerosol particles
since 1970.