Page 339 - Earth's Climate Past and Future

CHAPTER 17 • Climatic Changes Since the 1800s 315

The integrated temperature increase for the global
+0.5 ocean down to 3000 m for the last half of the 1900s is
0.06°C (Figure 17–10). Although this warming is much
Global temperature change (°C) 0 industrial era and stored in the deep ocean exceeds that
smaller than the 0.7°C rise in surface air temperature,
the amount of heat generated during the late part of the

stored in the atmosphere by more than a factor of 10.
This heat storage in the ocean is direct evidence of a
marked change in the heat balance of the entire climate
system compared to earlier decades.

Today, mountain glaciers cover 680 km of Earth’s land
–0.5 17-4 Mountain Glaciers 2
surface and represent about 4% of the total surface area
1900 1925 1950 1975 2000 of land ice on Earth today. Mountain glaciers at middle
Year
and high latitudes respond to local climate, primarily
FIGURE 17-9 Change in surface temperature since 1900 changes in summer temperature and also variations in
Reconstructions of global surface temperature based on winter snowfall. At lower latitudes, solar radiation and
surface station thermometer measurements show a warming precipitation are also important. Because of these dif-
trend of 0.7°C since 1900, interrupted by a small cooling from ferences in sensitivity, mountain glaciers in different
the late 1940s to the mid–1970s. (National Climate Data regions can show varying behavior. Individual glaciers
Center, NOAA, Asheville, NC.)

disagreeing mainly in the early 1900s when station cov- 1945 1955 1965 1975 1985 1995
erage was still sparse. Temperatures have warmed by 0.04
about 0.7°C over the last 110 years (Figure 17–9). Southern hemisphere
Temperatures were considerably cooler before the early
1900s, rose quickly during the 1920s to early 1940s,
stabilized or fell slightly from the late 1940s through
the late 1970s, and have again risen abruptly since 1980. –0.04

17-3 Subsurface Ocean Temperatures 0.04 Northern hemisphere
The ocean has the capacity to store enormous amounts 0
of heat for long intervals of time (companion Web site, Ocean temperature change
pp. 9–11). Changes in surface climate do not easily –0.04
penetrate below the upper 100 m that are mixed by
winds, but important information on deeper ocean
trends during the last half-century has come from a 0.02 World ocean
painstaking examination of millions of subsurface tem-
perature profiles by the climatologist Sid Levitus and 0
his colleagues.
From these observations a detailed picture has –0.02
emerged of the slow penetration of heat from the
atmosphere into the subsurface layers below 100 m.
Slow, downward molecule-by-molecule diffusion has FIGURE 17-10 Subsurface ocean warming The mean ocean
transferred some of the surface heat to depths of a few heat content of the upper 3000 m of the world ocean has
hundreds of meters, and near-horizontal movement increased in both the northern and the southern hemisphere
of heat has transferred even more heat into the subsur- and in the global average ocean by an average of 0.06°C.
face ocean. This heat enters the ocean at higher middle Despite the small size of this warming, the amount of heat
latitudes and moves toward the equator along layers stored in the ocean exceeds all the other reservoirs combined.
of equal density. Still slower penetration to depths of (Adapted from S. Levitus, J. I. Antonov, T. B. Boyer, and
1000 m or greater has also occurred in areas of deep C. Stevens, “Warming of the World Ocean,” Science 287 [2000]:
overturning like the subpolar North Atlantic Ocean. 2225–9.)