509
Carbon Dioxide, Trace Gases, and Climate Change
**Carl Sagan et al., “Anthropogenic Albedo
Changes and the Earth’ s Climate,” Science, 206, No.
4425 (1980), 367.
***An Early Start for Greenhouse Warming?”,
Science, Vol. 303, 16 January, 2004. This article is a
report on a paper given by paleoclimatologist
William Ruddiman at a meeting of the American
Geophysical Union in December 2003.
regions has yet appeared. Moreover, the cyclic pattern
of droughts found in tree rings is itself a subtle feature
that shifts from place to place within the broad region of
the study.*
Possible connections between solar
variability and climate would be much
easier to determine if researchers could
identify physical links between the Sun
and the lower atmosphere. Despite much
research, no connection between solar
variations and weather has yet been well
established. Apparent correlations have
almost always faltered when put to critical
statistical examination or when tested with
different data sets. As a result, the subject
has been characterized by ongoing
controversy and debate.
C O N C E P T C H E C K 2 0 . 6
Describe and briefly explain the effect on
global temperatures of the eruptions of EI
Chichón and Mt. Pinatubo.
How might volcanism lead to global
warming?
List two examples of climate change linked
to solar variability.
Human Impact
on Global Climate
So far we have examined four potential
natural causes of climate change. In
this section we discuss how humans contribute to global climate change. One
impact largely results from the addition to
the atmosphere of carbon dioxide and
other greenhouse gases. A second impact is
related to the addition of human-generated
aerosols to the atmosphere.
Human influence on regional and global
climate did not just begin with the onset of
the modern industrial period. There is solid
evidence that people have been modifying
the environment over extensive areas for
thousands of years. The use of fire and the
overgrazing of marginal lands by domesticated animals have reduced the abundance
and distribution of vegetation. By altering
ground cover, humans have modified such
important climatological factors as surface
3
2
1
D I D Y O U K N O W ?
Based on recent research that used
satellite data, there appears to be no
connection between changes in the
Sun’s brightness and recent global
warming. The scientists who carried out
this detailed analysis state that
variations in solar brightness measured
since 1978, which is as far back as these
measurements go, are too small to
have contributed appreciably to
accelerated global warming over the
past 30 years.
*Solar Variability, Weather, and Climate (Washington,
D.C.: National Academy Press, 1982), 7.
albedo, evaporation rates, and surface
winds. Commenting on this aspect of
human-induced climate modification, the
late astronomer Carl Sagan noted, “In
contrast to the prevailing view that only
modern humans are able to alter climate, we
believe it is more likely that the
human species has made a substantial and
continuing impact on climate since the
invention of fire.”**
Subsequently, these ideas were
reinforced and expanded upon by a
study that used data collected from
Antarctic ice cores. This research
suggested that humans may have started
to have a significant impact on atmospheric
composition and global temperatures
thousands of years ago.
Humans started slowly ratcheting up the thermostat as
early as 8000 years ago, when they began clearing
forests for agriculture, and 5000 years ago with the
arrival of wet-rice cultivation. The greenhouse gases
carbon dioxide and methane given off by these changes
would have warmed the world. . . .***
C O N C E P T C H E C K 2 0 . 7
How might people have altered climate
thousands of years ago?
Carbon Dioxide,
Trace Gases, and
Climate Change
Earlier you learned that carbon dioxide
(CO 2 ) represents only about 0.039 percent
of the gases that make up clean, dry air.
Nevertheless, it is a very significant component meteorologically. Carbon dioxide is
influential because it is transparent to
incoming short-wavelength solar radiation,
but it is not transparent to some of the
longer-wavelength outgoing Earth radiation. A portion of the energy leaving the
ground is absorbed by atmospheric CO 2 .
1
Two widely debated examples are briefly
described here.
SUNSPOTS AND TEMPERATURE.
Studies indicate that there have been prolonged periods when sunspots were absent
or nearly so. Moreover, these events
correspond closely with cold periods in
Europe and North America. Conversely,
periods characterized by plentiful sunspots
have correlated well with warmer times in
these regions.
Referring to these matches, some
scientists have suggested that such correlations make it appear that changes on the
Sun are important to climate change.
Other scientists seriously question this
notion. In part their hesitation stems from
subsequent investigations, using different
climate records from around the world,
that failed to find a significant correlation
between solar activity and climate. Even
more troubling is that no testable physical
mechanism exists to explain the
purported effect.
SUNSPOTS AND DROUGHT. A second
possible Sun–climate connection, on a
time scale different from the preceding
example, relates to variations in
precipitation rather than in temperature.
An extensive study of tree rings revealed
a recurrent 22-year rotation in the pattern
of droughts in the western United States.
This periodicity coincides with the previously mentioned 22-year magnetic cycle
of the Sun.
Commenting on this possible connection, a panel of the National Research
Council concluded:
No convincing mechanism that might connect so subtle
a feature of the sun to drought patterns in limited
Carbon Dioxide, Trace Gases, and Climate Change
**Carl Sagan et al., “Anthropogenic Albedo
Changes and the Earth’ s Climate,” Science, 206, No.
4425 (1980), 367.
***An Early Start for Greenhouse Warming?”,
Science, Vol. 303, 16 January, 2004. This article is a
report on a paper given by paleoclimatologist
William Ruddiman at a meeting of the American
Geophysical Union in December 2003.
regions has yet appeared. Moreover, the cyclic pattern
of droughts found in tree rings is itself a subtle feature
that shifts from place to place within the broad region of
the study.*
Possible connections between solar
variability and climate would be much
easier to determine if researchers could
identify physical links between the Sun
and the lower atmosphere. Despite much
research, no connection between solar
variations and weather has yet been well
established. Apparent correlations have
almost always faltered when put to critical
statistical examination or when tested with
different data sets. As a result, the subject
has been characterized by ongoing
controversy and debate.
C O N C E P T C H E C K 2 0 . 6
Describe and briefly explain the effect on
global temperatures of the eruptions of EI
Chichón and Mt. Pinatubo.
How might volcanism lead to global
warming?
List two examples of climate change linked
to solar variability.
Human Impact
on Global Climate
So far we have examined four potential
natural causes of climate change. In
this section we discuss how humans contribute to global climate change. One
impact largely results from the addition to
the atmosphere of carbon dioxide and
other greenhouse gases. A second impact is
related to the addition of human-generated
aerosols to the atmosphere.
Human influence on regional and global
climate did not just begin with the onset of
the modern industrial period. There is solid
evidence that people have been modifying
the environment over extensive areas for
thousands of years. The use of fire and the
overgrazing of marginal lands by domesticated animals have reduced the abundance
and distribution of vegetation. By altering
ground cover, humans have modified such
important climatological factors as surface
3
2
1
D I D Y O U K N O W ?
Based on recent research that used
satellite data, there appears to be no
connection between changes in the
Sun’s brightness and recent global
warming. The scientists who carried out
this detailed analysis state that
variations in solar brightness measured
since 1978, which is as far back as these
measurements go, are too small to
have contributed appreciably to
accelerated global warming over the
past 30 years.
*Solar Variability, Weather, and Climate (Washington,
D.C.: National Academy Press, 1982), 7.
albedo, evaporation rates, and surface
winds. Commenting on this aspect of
human-induced climate modification, the
late astronomer Carl Sagan noted, “In
contrast to the prevailing view that only
modern humans are able to alter climate, we
believe it is more likely that the
human species has made a substantial and
continuing impact on climate since the
invention of fire.”**
Subsequently, these ideas were
reinforced and expanded upon by a
study that used data collected from
Antarctic ice cores. This research
suggested that humans may have started
to have a significant impact on atmospheric
composition and global temperatures
thousands of years ago.
Humans started slowly ratcheting up the thermostat as
early as 8000 years ago, when they began clearing
forests for agriculture, and 5000 years ago with the
arrival of wet-rice cultivation. The greenhouse gases
carbon dioxide and methane given off by these changes
would have warmed the world. . . .***
C O N C E P T C H E C K 2 0 . 7
How might people have altered climate
thousands of years ago?
Carbon Dioxide,
Trace Gases, and
Climate Change
Earlier you learned that carbon dioxide
(CO 2 ) represents only about 0.039 percent
of the gases that make up clean, dry air.
Nevertheless, it is a very significant component meteorologically. Carbon dioxide is
influential because it is transparent to
incoming short-wavelength solar radiation,
but it is not transparent to some of the
longer-wavelength outgoing Earth radiation. A portion of the energy leaving the
ground is absorbed by atmospheric CO 2 .
1
Two widely debated examples are briefly
described here.
SUNSPOTS AND TEMPERATURE.
Studies indicate that there have been prolonged periods when sunspots were absent
or nearly so. Moreover, these events
correspond closely with cold periods in
Europe and North America. Conversely,
periods characterized by plentiful sunspots
have correlated well with warmer times in
these regions.
Referring to these matches, some
scientists have suggested that such correlations make it appear that changes on the
Sun are important to climate change.
Other scientists seriously question this
notion. In part their hesitation stems from
subsequent investigations, using different
climate records from around the world,
that failed to find a significant correlation
between solar activity and climate. Even
more troubling is that no testable physical
mechanism exists to explain the
purported effect.
SUNSPOTS AND DROUGHT. A second
possible Sun–climate connection, on a
time scale different from the preceding
example, relates to variations in
precipitation rather than in temperature.
An extensive study of tree rings revealed
a recurrent 22-year rotation in the pattern
of droughts in the western United States.
This periodicity coincides with the previously mentioned 22-year magnetic cycle
of the Sun.
Commenting on this possible connection, a panel of the National Research
Council concluded:
No convincing mechanism that might connect so subtle
a feature of the sun to drought patterns in limited