Page 352 - Earth's Climate Past and Future

328 PART V • Historical and Future Climate Change

FIGURE 18-3 Brief volcanic
1991 cooling and El Niño warming Large
+0.5 volcanic explosions and major El
Volcanic explosions Pinatubo
1981 Niño events cause short-term changes
El Chichon that can be large enough to be
detected in the instrumental
1963
Global temperature change (°C) 0 (Adapted from National Climate Data
1912
temperature record but leave the
Agung
Katmai
long-term baseline trend unaffected.
Center, NOAA, Asheville, NC.)

1926 Strong El Ninos 1983 1998
~
–0.5
1900 1925 1950 1975 2000
Year

chemicals of various kinds, and sulfate and carbon beneath Earth’s surface. At first coal was the main fuel,
aerosols. but later on oil and natural gas became the major
sources of energy. Gradually the carbon released by
fossil fuels came to exceed the amount produced by
18-4 Carbon Dioxide (CO )
2 land clearance by ever-larger amounts. Today industrial
Bubbles of ancient air trapped in ice and instrumental
measurements begun by the geochemist Charles Keeling
in 1958 show an accelerating rise in the CO concentra- 380
2
tion during the last two centuries. By the early 2000s
the concentrations had passed 380 ppm, well above the 360
180–300 ppm range of natural (glacial-interglacial) varia-
tions (Figure 18–4A). 340
The additional carbon emitted from human activi-
ties has come mainly from two sources (Figure 18–5).
Throughout the late 1700s and most of the 1800s, the 320
main source of carbon was clearing of forests to meet
the needs of an increasing human population: farmland 300
for agriculture, wood for home heating, and charcoal to
fuel the furnaces of the Industrial Revolution. Cutting
and burning of forests (and resulting emission of CO ) CO 2 (ppm) 280
2
were particularly intensive in eastern North America
during that interval. 260
After 1900, most of the extra carbon added to the
atmosphere came from fossil fuel reservoirs buried
240 Natural
glacial-interglacial
range
FIGURE 18-4 Preindustrial and anthropogenic CO The 220
2
combined atmospheric CO record from bubbles in ice cores
2
and from instrument measurements since 1958 shows an 200
accelerating increase of CO in the last 200 years above the
2
natural baseline of 280 ppm. (Adapted from Intergovernmental
Panel on Climate Change, “Climate Change 2007: The Physical 180 1600 1800 2000
Science Basis” [Geneva: World Meteorological Association, 2007].) Year