Print this pageGeological Perspectives of Global Climate Change: Introduction and Overview*
By
Gerhard, L.C.,1 W.E. Harrison, 1 and B.M. Hanson2
Search and Discovery Article #70007 (2001)
1Kansas Geological Survey Lawrence, Kansas, U.S.A. ([email protected]; [email protected])
2Independent Petroleum Producer (Deceased)
*Adapted for online presentation of article of same title by same authors in AAPG Studies in Geology No. 47, entitled “Geological Perspectives of Global Climate Change,” now available from AAPG’s online bookstore (http://bookstore.aapg.org).|
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of Estimating Ancient tNatural Variability and Records of Change
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of Estimating Ancient tNatural Variability and Records of Change
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of Estimating Ancient tNatural Variability and Records of Change
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of Estimating Ancient tNatural Variability and Records of Change
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Global
climate has varied since the most primitive atmosphere developed on
earth billions of years ago. This variation in climate has occurred on
all timescales and has been continuous. The sedimentary rock record
reflects numerous sea-level changes, atmospheric compositional changes,
and Geologic
processes are not in equilibrium. Geologic processes are one set of
drivers for climate and therefore climate cannot be in equilibrium. This
makes assessing any cumulative human impact on climate difficult. What
is the range of natural global climatic variability? What percentage of
this may be due to human-induced activities? We may perceive the
activities of humans to have the greatest impact on global climate
simply because we are the advanced life form on earth. Perhaps it is a
human trait to assume that the consequences of mankind on global climate
must be significantly more important than the impact of “natural
processes.” Geology is the one scientific discipline that routinely
works backward through significant periods of time to evaluate earth’s
natural processes. Our discipline brings both data and interpretation to
the debate of the past history of climate, greenhouse gases, and global
The
chapters of AAPG Studies in Geology No. 47, Geological Perspectives
of Global climate Change (herein noted as GPGCC, 2001), are
arranged to take the reader through examples of geologic climate drivers
(“Climate Drivers”), documentation of a number of methodologies for
establishing ancient One
of the most difficult concepts to communicate to the lay public is the
scale of Several general statements are appropriate about natural systems. Climate can vary rapidly and over a range that can have a profound influence on human society. There are predictable geologic effects of climate change that occur in second through fourth order changes (Figure 1), such as sea-level changes, rates of glacial movement, ecosystem migration, methane hydrate formation, and agricultural productivity. Finally, we are able to predict that the next ice age cannot take place unless additional global warming occurs. Such warming must be sufficiently large so that the ice of the Arctic Ocean is thawed, thus providing a moisture source for the immense snow and ice accumulations necessary to build continental-scale glaciers (Ewing and Donn, 1956).
Climate
drivers can be categorized by the dual attributes of range of
Figure 1 Caption (continued): First-order
climate controls: Earth has a
life-supporting climate because of its distance from the sun, solar
luminosity, and the evolution of a greenhouse atmosphere of water vapor,
methane, CO2, and other gases that Figure 1 Caption (continued): Second-order climate controls: Distribution of oceans and continents on the surface of the earth controls ocean currents, which distribute heat. This fundamental concept (Gerhard and Harrison, Chapter 2, GPGCC, 2001) explains the 15o–20oC climate variations over hundreds of million of years (Lang et al., 1999; Frakes, 1979, p. 203). Such variations are exemplified by the two major earth cycles between glacial “icehouse” and warm “greenhouse” states. The late Precambrian “icehouse” evolved into the Devonian “greenhouse,” then the Carboniferous “icehouse,” then the Cretaceous “greenhouse,” which evolved to the present “icehouse” state. Redistribution of heat around the earth is determined by the presence of equatorial currents that keep and thrust warm water masses away from the poles. Blockage of such currents, which permits the formation of gyres that move warm waters to the poles, creates the setting that allows continental-scale glaciation. Figure 1 Caption (continued): Third-order
climate controls: Solar insolation
variability has emerged as a major climate driver, as are the orbital
variations that change the distance between the earth and the sun (Hoyt
and Schatten, 1997; Frakes, 1979, p. 9; Pekarek, Chapter 1, GPGCC,
2001; Fischer, 1982; Berger et al., 1984). In addition, large-scale
changes in ocean circulation through changes in current structure can be
significant climate drivers (Broecker, 1997, 1999). Large-scale ocean
tidal cycles may drive climate, including the large-scale maximum and
minimum associated with the Medieval Climate Optimum and the Little Ice
Age, on an 1800-year cycle with a 5000-year modulation (Keeling and
Whorf, 2000). These drivers may cause Figure 1 Caption (continued): Fourth-order
climate controls: There are many
drivers that control small The
sun is the primary source of energy for the climate of the earth.
Earth’s distance from the sun, a function of the geometry of the solar
system, is the major factor controlling the base We consider these two effects, solar-system geometry and fundamental greenhouse conditions, to be first-order climate controls (Figure 1). Second-order
climate control is by the distribution of continents and oceans upon the
planet (Gerhard and Harrison, Chapter 2, GPGCC, 2001) (Figure
1). The earth has undergone several cycles of icehouse and
greenhouse climates, from at least the Vendian (late Precambrian)
through the present. Glacial activity is reasonably interpreted at
various locations as early as about 3 billion years ago (Crowell, 1999).
Third-order
Variations
in solar energy reaching the earth’s surface modify the climate.
Several factors control the influx of solar energy, including variations
in (1) the earth’s albedo, (2) earth’s orbit and rotation, and (3)
solar energy output. Potential In the short time since 1978, direct measurement of total solar irradiance (TSI) by satellites has shown cyclical variations in solar energy of 0.1% in conjunction with the 11-year sunspot cycle. Indirect evidence from the sun and other sunlike stars indicates that TSI has had significantly greater variation as the sun goes through its energy output cycles. Correlations
between climate and TSI variations are statistically solid. Small
variations in TSI initiate indirect mechanisms on earth that yield
climate changes greater than that predicted for the TSI change alone. At
least three solar variables are known to affect earth’s climate: (1)
TSI, which directly affects temperatures; (2) solar ultraviolet
radiation, which affects ozone production and upper atmospheric winds;
and (3) the solar wind, which affects rainfall and cloud cover, at least
partially through control of earth’s electrical field. Each affects
the earth’s climate in different ways, producing indirect effects that
amplify small changes in TSI. Individually, they do not cause the entire
observed climatic changes. Collectively, they create changes. Because
solar forcing of earth’s climate is still an emerging science, some
effects may not be fully understood. Many of these changes take place in
a more or less regular cycle, as if the sun itself has periodic changes.
Earth orbital changes are periodic. The most commonly observed solar
cycle is the 11-year sunspot cycle. Statistically optimized simulations
suggest that direct solar forcing can account for 71% of the observed
The world ocean is vast, and owing to the specific heat of water, it contains vast amounts of thermal energy. Much of that energy is transferred around the earth through ocean currents. Some is transmitted to and from the atmosphere and controls local weather. Ocean currents are driven by wind, the Coriolis effect, and thermohaline circulation (which depends on density differences of waters entering the ocean). Fresh waters are lighter than saline waters, and warm waters are lighter than cold waters. The density of a water mass will determine whether it rises or sinks in the water column. Broecker
(Chapter 4, GPGCC, 2001) suggests that warm events after glacial
events provide low-salinity, thus low-density, meltwaters into the
ocean, which tend to float rather than sink in areas where sinking (downwelling)
normally takes place. This action interferes with total normal oceanic
circulation; for instance, the Gulf Stream may be diverted eastward by
meltwaters from the North American arctic, depriving England and
northern Europe of heat now moderating their climate. If massive events
such as floods of fresh water backed up in proglacial lakes were to
spill into the ocean, then very rapid climate changes could take place
by changing the ocean circulation patterns. Broecker argues that at
least two such events took place near the beginning of the present
interglacial stage, with dramatic (up to 4O-5OC)
rapid Broecker
postulates that this process would become effective around the time that
atmospheric carbon-dioxide concentrations reach about 750 parts per
million (ppm), or about twice ambient. He believes that such
concentrations might be reached by 2100. If this is a valid cause and
effect, then at some time in the future, assuming that the current
interglacial stage continues to full melting of the Arctic Ocean,
Broeker expects such dramatic climate changes to occur, regardless of
whether human influence is shown to affect climate. If Broecker is
correct, then the process to the next “flickering switch” climate
change is toward the end of this century. If he is not correct in his
assumption of human impact on climate, then the change could occur any
time in the next thousand or more years. Fitzpatrick (1995) has
discussed such changes without regard to thermohaline circulation. There
are few other explanations for the dramatic A large number of smaller-scale geological climate drivers exist. Among these are volcanic eruptions, meteorite impacts, solar storms and flares, shorter solar cycles, small orbital changes, tectonism (mountain building and erosion), weathering of rocks, small ocean-circulation changes (i.e., La Niña and El Niño oscillations, North Atlantic Oscillation, etc.) and, although not geological, human interventions through increased greenhouse gas emissions. We consider these effects, which may alter climate up to perhaps 3O or 4OC, to be fourth-order climate drivers (Figure 1). Some new concepts involving sudden release of massive amounts of methane through methane hydrate disassociation along continental edges have been advanced (Katz et al., 1999). Ruddiman (1997) has compiled an extensive collection of papers detailing tectonism. Well-known effects of the 1883 Krakatoa eruption that affected climate for two years or more and the recent Pinatubo eruption in the Philippines include the particulates blown into the upper atmosphere that caused cooling to take place. The recent scientific literature is crowded with examples of short-term or moderate- to low- intensity, fourth-order climate-change demonstrations. The public media have documented El Niño and La Niña events. We will not further elaborate on details of fourth-order climate drivers except to present one discussion of the role of human activities’ potential for climate effects (Mackenzie et al., Chapter 3, GPGCC, 2001). Mackenzie
et al. in Chapter 3 have modeled the cycles of carbon, nitrogen,
phosphorus, and sulfur with the purpose of extracting human contribution
to those cycles over the last 300 years. Their conclusions are that
fossil-fuel emissions, land-use changes, agricultural fertilization of
croplands, and organic sewage discharges to aquatic systems, all coupled
with a slight Mackenzie et al. have modeled the effects of the proposed Kyoto protocol on future carbon-dioxide (CO2) concentrations. Despite a reduction in emissions of CO2 in their model, concentrations of CO2 would continue to build because of the continuous emissions of fossil-fuel and land-use CO2 to the atmosphere, albeit at reduced rates for the former, complex interactions, and a sluggish response of the system to the reduction in emissions. This would be in part due to continued rise of CO2 in the atmosphere owing to land-use changes and to the fact that CO2 has an approximate 10-year residence time in the atmosphere. Mackenzie et al. suggest that the Kyoto approach might be useful in reducing the rate of increase of future atmospheric CO2 concentrations, but only if the physical and biogeochemical mechanisms of redistribution of CO2 among the atmosphere, land, and ocean do not significantly change from the present. Other effects that may occur include reduced precipitation of carbonate minerals in biotic frameworks and increased transport of organic carbon, nitrogen, and phosphorus into coastal sediments. They suggest that human factors could impact mineral and organic carbon sedimentation, as already seen in lakes in industrialized countries. Methods
of estimating ancient The geologic record contains a large number of clues about former climate, with which we must compare any changes that we estimate might occur, either naturally or human induced. The methods are not infallible, but the vast majority of the proxies used to interpret past temperatures agree well enough to build a consensus about the more recent geologic past, and general acceptance of large-scale changes in the more distant past. The accuracy of interpretations of past climates declines as we go farther back into the past. Pleistocene climates are well documented, but those of 600 million years ago are less well documented, and those of billions of years ago are poorly documented. It is the nature of the geologic record that records become progressively destroyed by erosion and tectonic cycling as time passes. Parrish (1998) gives an excellent summary of paleothermometry methods. One
possible means to ensure that Isotopic data are presented for several ice cores collected from three low-latitude but high-altitude locations of the Tibetian Plateau and from the Andes Mountains of South America. The results show that the Tibetian Plateau area experienced warm climates (like that of today) about 3000 years ago. In the Andes, such conditions existed about 5000 years ago. Thompson suggests that tropical warming, as demonstrated by significant losses of ice mass from low-latitude glaciers, is enhanced by (1) evaporation of oceanic water and (b) the release of latent heat (due to condensation) at higher elevations. He also proposes that water vapor, the most important greenhouse gas on earth, is pumped into the atmosphere at low latitudes. Any increases in CO2 levels may contribute to an increasing global inventory of water vapor and may strongly influence global changes. The
technique developed by Nagihara and Wang (Chapter 6, GPGCC, 2001)
relies on data from boreholes drilled into the seafloor as a means to
determine variation in bottom-water The
variation of BWT is compared with Key West surface air temperatures
collected between 1850 and the late 1990s and found to be in good
agreement. The air- This technique requires that (1) borehole temperatures are free of drilling disturbances, (2) a sufficient number of measurements are made over small vertical depth intervals, and (3) effects of sedimentation, erosion, and pore fluid movement can be accurately determined. When such conditions can be satisfied, BWT-reconstructed history curves may become very powerful tools for assessing global climate change. Coralline sponges or sclerosponges live in tropical marine waters but cannot compete with reef-building corals and primarily exist at depths to which light does not greatly penetrate (i.e., below the photic zone). These organisms precipitate calcium-carbonate (CaCO3) growth rings from seawater to form their exoskeleton structure. Hughes and Thayer (Chapter 7, GPGCC, 2001) present evidence that Mg:Ca and Cl:Ca elemental ratios of the precipitated CaCO3 material have potential application for evaluating past seawater temperatures and salinity conditions. In addition, these workers review the literature concerning precipitated CaCO3 in fossil ostracodes, mussels, bivalves, etc., and paleotemperature conditions. A
sclerosponge began growing on a submerged marker plate that was attached
to a submarine cave wall in July 1989, and it was collected for study
nine years later. Chemical analysis of the sectioned specimen was made
using energy dispersive spectroscopy (EDS), and elemental ratios were
determined at discrete locations across individual growth bands.
This
technique has potential as a means to evaluate marine paleotemperature
and paleo salinity conditions. Because individual sclerosponges can live
for centuries, it may be possible to reconstruct high-resolution
seawater In addition to techniques that may reveal paleoclimate information from marine settings, some lines of evidence are based exclusively on terrestrial organisms (Ashworth, Chapter 8, GPGCC, 2001). Insects, specifically fossil beetles, provide such evidence. The estimated 1 million to 7 million species of beetles account for approximately 20% of all species on earth. They are found in almost all habitats, ranging from high mountain settings to rain forests. Beetles occupied the interior part of Antarctica until the Neogene, when the growth of the polar ice sheets resulted in their extinction. The fossil record indicates that beetle diversity has not increased due to rapidly changing climate changes. Hundreds of species now in existence have been reported from Pleistocene and Holocene studies. This indicates that different species of beetles do not readily develop over extended periods of time and suggests a pattern of stasis or constancy. A fossil beetle assemblage collected from northern Greenland demonstrates an unusual level of stasis through approximately 2 million years, even though the climate at that time was significantly warmer than that of today. The number of species remained relatively constant through several episodes of glaciation. Beetles are highly mobile insects, and their most apparent response to variation in climate is migration from one location to another. This is well illustrated by the replacement (21,500 b.p.) of a forest fauna along the North American Laurentide ice sheet by a glacial fauna when temperatures were approximately 10O-12OC below current ones. When the ice sheet receded (approximately 12,500 b.p.), a forest fauna returned. Overall, beetles have survived global climatic changes due to their mobility, but reduction in areas suitable for habitat make future extinctions more likely. The use of fossil biosensors to estimate paleoatmospheric levels of CO2 is an area of active research, and Chapter 9, GPGCC, 2001, by Kurschner et al. is especially interesting due to early results as well as potential applications. The technique is based on the fact that all higher land plants rely on stomata to regulate the exchange of gas between the atmosphere and leaf tissue. Herbarium materials collected during the last 200 years and growth experiments conducted under preindustrial conditions all demonstrate an inverse relationship between stomata development and atmospheric levels of CO2. Elevated levels of CO2 produce fewer stomata than do decreased levels. SI (Stomatal Index) values for birch trees dated (by radiocarbon) at 10,070 years are in the 12 to 14 range and correspond to CO2 levels of approximately 240 to 280 parts per million, volume (ppmv). Birch trees that are 9370 years old have SI values of 6 to 8 and indicate CO2 concentrations of 330-360 ppmv. Thus, these findings indicate an 80-90 ppmv variation in naturally occurring CO2 levels over a 700-year period. Additionally, SI data suggest a dramatic change of 65 ppmv CO2 levels in less than a century. Several lines of evidence indicate that early to middle Miocene time was one of the warmest periods of the entire Cenozoic. Kurschner et al. studied exceptionally well preserved fossil angiosperm materials of middle Eocene age and found that SI values were elevated. By extrapolation of SI data, the authors offer an estimate of 450-500 ppmv for the CO2 level of the middle Eocene atmosphere. Based on these results and those obtained over the last few years, it appears that plant biosensor technology has good potential as a proxy for assessing paleoatmospheric CO2 concentration levels. Natural variability and records of change Interpretation of geological evidence for climate change results in development of curves that illustrate climate change through time and effects of climate change through time. This section offers four papers that document climate changes over the last few million years (Bluemle et al., Chapter 10, GPGCC, 2001), effects of climate change on shorelines and thus population in northern Europe (Harff et al., Chapter 12, GPGCC, 2001), sea-level changes that are a global response to climate variability (Shinn, Chapter 13, GPGCC, 2001), and, finally, some biogeochemical effects of climate variability (Yates and Robbins, Chapter 14, GPGCC, 2001). In a previously published article, Bluemle et al. (1999; also Chapter 10, GPGCC, 2001) have recreated the Pleistocene climate variability in sufficient detail to draw conclusions about the impacts of fourth-order climate changes. Pleistocene glaciations are reflected in second- and third-order drivers (Figure 1), but have superimposed on them all of the variability of fourth-order drivers. Bluemle
et al. present several lessons. First, over the last 60 million years,
in central Europe, The
second lesson from the paper by Bluemle et al. involves the range of
variation of Third,
none of these General
circulation models (GCMs) are the basis for much discussion of the role
of CO2 in the atmosphere and as a climate driver. These
models tend to examine relatively short time spans for their historical
perspectives, and predict atmospheric and climate changes from that
perspective. The advent of data from ice cores on Greenland has provided
a time series of data that might be usable to extend the GCMs’
historical perspective and to validate algorithms. Before using the
data, a statistical validation of the data set can identify anomalies in
the data or problems in data quality and continuity. Davis and Bohling
(Chapter 11, GPGCC, 2001) have used 20-year averages to examine
oxygen 18O data from the Greenland Ice Sheet Project II
(GISP2) “core.” The results of their analysis demonstrate that the
last 10,000 years exhibit a general cooling trend and that the current
rate of increase in temperatures and warming trend are not unusual
compared to the last 10,000 years. Further, past periods of consistently
changing These
are important points. That the current rate of Geological interpretations are four-dimensional, that is, they consider time as well as space. Many lay people wrongly assume that sea-level effects are unidirectional, whereas they are actually relative (that is, land elevation changes as well as actual sea level). Harff et al. in Chapter 12, GPGCC, 2001, demonstrate that the rise and fall of sea level in the Baltic Sea region is a function of climate-driven eustatic sea-level changes coupled with tectonism and glacio-isostatic rebound. For coasts in the north (Baltic shield), glacio-isostatic rebound is clearly dominant, with rates of uplift up to +9 mm/year. In the south, there is a small amount of subsidence added to a climate-driven eustatic sea-level rise that totals a relative sea-level rise of 2.5 mm/year. In comparison, Shinn (Chapter 13, GPGCC, 2001) demonstrates that the rate of sea-level rise in Florida is on the order of 10-20 cm per 100 years (1-2 mm per year). This means the area south of the Baltic Sea, a densely populated area on a low-lying coastal plain, is faced with climatically controlled retreating shorelines. Harff et al. lay the groundwork for development of strategies for the protection of subsiding coastal areas. The pattern and high rate of sea-level change in the Baltic qualify the Baltic Sea to serve as a “model ocean” for studies that reveal the effects of natural geological processes, including climate change, on human populations along coastlines. Parenthetically, measurement of sea level is very difficult because of the roughness of the water surface, continually varying tides, slow tectonic movement of the land surface, land subsidence by water withdrawal, and wind effects. Continual improvement in techniques for measurement of actual sea level are critical to predicting the effects of climate change on coastal regions. One issue that receives popular attention and is of very personal interest to those who live on low-relief coral atolls and islands in the Pacific is the rate and magnitude of sea-level changes to be expected under various climate scenarios. The best way to evaluate such changes is to look at the record of the recent past, the Pleistocene. Shinn (Chapter 13, GPGCC, 2001) has summarized evidence to demonstrate that the last interglacial sea-level rise maximum was about 6 m above the present sea level, between about 135,000 and 115,000 years ago (Stage 5e, Shinn’s, figure 1). This gives a reasonable maximum that can be expected for the current interglacial, that is, based on the assumption that much polar glacial ice will have melted by the end of the interglacial, a 6-m sea-level rise can be predicted. Shinn uses elevated coral reefs and wave-cut notches to correlate the highstand. Much more difficult, according to Shinn, is correlation of lowstands and identification of the total range of sea-level change between glacial (lowstand) and interglacial (highstand) events. Using new diving technologies and accessing resource exploration seismic and drilling data as well as research drilling data, Shinn has documented lowstand beaches and coral reefs whose elevations are approximately 80 m below present sea level. However, his figure 1 indicates that the last lowstand was approximately 130 m below standard. Thus a minimum range for sea-level change through a full glacial cycle is 86 m in tropical areas where glacial rebound is not significant. Of
interest is that the sea-level record (Shinn’s figure 1)
approximates the “sawtooth” effect seen in the Whether human-induced CO2 is a significant factor in climate change or not, many businesses are preparing for political intervention in industrial processes to reduce CO2 emissions. Scientists must recognize that scientific conclusions or data may not be a driver for political action; rather, social and economic issues affecting the immediate well-being of voting citizens supersede more academic approaches. In many cases, scientists have found it difficult to communicate sophisticated and complex conclusions to the lay public and government. Frequently, immediate needs of government supersede what scientists may argue is prudent action, and public perception of scientific issues may deviate from the science. Because of all those factors, it is sometimes prudent to look at technical solutions to issues, regardless of their scientific merit. If political action takes place to reduce anthropogenic emission of CO2, it is likely best to lead in introducing sound methods that are the most effective and the least expensive. Therefore, we present several papers that address technology of carbon sequestration and hopefully will help the political process appreciate the costs and effects of considered actions. Sequestration is the common term used to describe methods for placing CO2 where it cannot affect atmospheric concentrations. This book contains papers that describe two possible methods. The first, an original piece of scientific research into a generally difficult problem of the origin of lime mud in the ocean (Yates and Robbins, Chapter 14, GPGCC, 2001), documents that microbial activity in the ocean may be responsible for generation of lime mud. The chemistry of organic catalysis takes up CO2 and thus provides a possible method to sequester CO2 through sedimentation in the shallow ocean. The details of the original research are somewhat technical and may be difficult for the lay scientist to follow, but their summary provides the reader with an overview of the potential for a new geological sequestration process. Biologic catalysis can remove CO2 from water while producing lime mud, either in sheaths around the microbe or on (or near) the surfaces of cells without sheaths. Both processes result in direct precipitation owing to the microchemical conditions surrounding the microbe. This process sheds light on the controversial question of production of large amounts of lime mud that cannot be accounted for by controlled biologic precipitation or by skeletal abrasion and disintegration. The
second paper (Bachu, Chapter 15, GPGCC, 2001) addresses use of
subsurface (underground) sedimentary rocks as a long-term (or
“permanent”) host for anthropogenic CO2 as one of several
possible means to dispose of unwanted CO2. The physical state
of CO2 changes phase, depending on Using statistical methods, Kotov (Chapter 16, GPGCC, 2001) has examined the Greenland ice-core record for patterns that can be projected into the future. Using the geological past to understand the present is part of every geologist’s training, as is the reverse. Statistical analysis of past climate variability from oxygen isotope and other ice-core data suggests that there are patterns within the apparently chaotic data. Testing these patterns suggests that there is some regularity to climate patterns, and it is this statistically identifiable regularity that forms the basis for future projection of natural variability. Study
of the past permits Kotov to predict the future. The present climate is
not significantly different from much of the past, and projected future
Corroboration of this prediction appears in a very recent related paper (Keeling and Whorf, 2000) about 1800-year tidal cycles that may be responsible for the twelfth-century climate maximum and fifteenth-century climate minimum (Medieval Climate Optimum and Little Ice Age, respectively). Based on their analysis of large-scale tidal cycles, these workers predict that continued natural warming is likely to “continue in spurts for several hundreds of years,” before the next cooling episode starts. It is important to note that Keeling and Whorf expect that, “Even without further warming (from greenhouse gases), . . . this natural warming at its greatest intensity would be expected to exceed any that has occurred since the first millennium of the Christian era . . . independent of any anthropogenic influences.” It is usually significant when two completely different methodologies arrive at a similar conclusion independently of each other, and thus we offer these observations to assist readers in making up their own minds on this matter. The
paper by Idso (Chapter 17, GPGCC, 2001) is one of two reprinted
in that volume by permission of the original publishers. It represents
an unusual set of observations, measurements, and interpretations
carried out while the author was studying meteorological processes over
a two-decade period, wherein he and his colleagues quantified the
climatic consequences of several naturally occurring atmospheric
phenomena: variations in atmospheric dust content, cyclical patterns of
solar radiation receipt, the greenhouse effect of water vapor over the
desert Southwest of the United States, etc. This paper, originally
published in Climate Research in 1998, represents one of the
major studies to question the relationship between increasing CO2
levels in the atmosphere and the concurrent increase in mean annual
global surface air Based
on measurements resulting from eight types of “natural experiments,”
Idso deduced that raising the air’s CO2 concentration from
300 to 600 ppm should result in an increase in mean surface air
Idso
also provides a summary of relative Of
particular interest in this paper are Idso’s descriptions of
mechanisms that might enhance the overall cooling properties of the
earth if global temperatures were to increase slightly. These negative
feedbacks include the likelihood that a 10% increase in earth’s low
cloud cover would completely cancel the warming predicted to result from
a doubling of the air’s CO2 content, plus the fact that a
warmer and CO2-enriched world would produce clouds with an
increased liquid water content and increased levels of cloud
condensation nuclei (which allow clouds to last longer and cool the
earth longer). And in what may be considered a bit of natural irony,
some of these meteorological phenomena can be triggered by elevated
levels of CO2 alone, without an accompanying The final paper in this volume is a philosophic view of the issue of climate change and of the effects of humankind on the earth in general. Jenkins (Chapter 18, GPGCC, 2001) addresses the myths of stability of natural systems and the reality of human technological prowess to adapt and prosper in naturally dynamic and unpredictable systems. While developing his thesis of natural variability and yet understanding the public perception of an unchanging world, Jenkins demonstrates the fallibility of assuming stasis. Particularly poignant are his arguments that although warming may be a bother, significant cooling, geologically predictable, could be disastrous for feeding the vastly increasing numbers of people on this planet. Warming may well increase the problems of sea-level rise and provision of fresh water. The natural rates of change may well be accelerated by human influence but likely will not move in different directions. Humans may easily adapt to changes in their environment by using technology and the inherent flexibility of intelligent beings. Once people accept that the world is not dynamically stable, on any timescale, then comprehensive adaptations can begin. Geologists know the earth is a single dynamic system, billions of years old, that is not in equilibrium. A flat, featureless, and uninteresting earth would be the result of equilibrium. Because change is constant, inevitable, and interesting, humankind must embrace change rather than fear it. Adaptation to the changes that continually occur on our planet requires flexibility, planning, and acceptance of the earth-system constraints. Political processes cannot change earth dynamics. Changes that do take place must be placed in context of their real effects. And finally, a major and recurring theme of this volume bears repeating once more. Climate drivers are variable in both time and intensity (Figure 1) and--regardless of the largely political belief that human consequences on global climate are pronounced--human influences are of comparatively low intensity and take place over short time spans. The nonequilibrium systems that control natural phenomena on earth very likely dwarf man’s ability to affect climatic conditions on a global scale.
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Geological Perspectives of Global Climate Change (GPGCC) 2001 Chapter 1. Solar forcing of earth’s climate, by Alfred H. Pekarek. Chapter 2. Distribution of oceans and continents: a geological constraint on global climate variability, by Lee. C. Gerhard and William E. Harrison. Chapter 3. Recent past and future of global carbon cycle, by Fred T. Mackenzie, A. Lerman, and L.M.B. Ver. Chapter 4. Are we headed for a thermohaline catastrophe?, by Wallace S. Broecker. Chapter
5. Stable isotopes and their relationship to Chapter 6. Century-scale variation of seafloor temperatures inferred from offshore borehole geothermal data, by Seiichi Nagihara and Kelin Wang. Chapter 7. Sclerosponges: potential high-resolution recorders of marine paleotemperatures, by Gary B. Hughes and Charles W. Thayer. Chapter 8. Perspectives on Quaternary beetles and climate change, by Allan C. Ashworth. Chapter 9. Using fossil leaves for the reconstruction of Cenozoic paleoatmospheric CO2 concentrations, by Wolfram M. Kürschner, Friederike Wagner, David L. Dilcher, and Henk Visscher. Chapter 10. Rate and magnitude of past global climate changes, by John Bluemle, Joseph M. Sabel, and Wibjörn Karlén. Chapter
11. The search for patterns in ice-core Chapter 12. Sea-level change in the Baltic Sea: interrelation of climatic and geological processes, by Jan Harff, Alexander Frischbutter, Reinhard Lampe, and Michael Meyer. Chapter 13. Coral reefs and shoreline dipsticks, by E.A. Shinn. Chapter 14. Microbial lime-mud production and its relation to climate change, by K.K. Yates and L.L. Robbins. Chapter 15. Geological sequestration of anthropogenic carbon dioxide: applicability and current issues, by Stefan Bachu. Chapter 16. Near-term climate prediction using ice-core data from Greenland, by Sergy R. Kotov. Chapter 17. Carbon-dioxide-induced global warming: a skeptic’s view of potential climate change, by Sherwood B. Idso. Chapter 18. Potential impact and effects of climate change, by David A.L. Jenkins. |
Figure
1. Climate drivers: First-, second-, third-, and fourth-order climate
controls.