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Priem, H. (2000): Climate Change: the human influence analysed.- European Council of Skeptical
Organisations (ECSO), Rossdorf (Germany), 2-3 September 2000.
(http://www.ozemail.com.au/~hughesw7/hpriem.htm)
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Harry N.A. Priem autor
http://www.ozemail.com.au/~hughesw7/hpriem.htm
Climate Change: the human influence analysed
This paper is based on an invited lecture at the meeting of the European Council of Skeptical
Organisations (ECSO) on the occasion of the inauguration of the European Center for
Inquiry, Rossdorf (Germany), 2-3 September 2000
Harry N.A. Priem
Dept. of Earth Sciences Utrecht University, P.O. Box 80021, 3508 TA Utrecht, and
Global Institute for the Study of Natural Resources, The Hague (The Netherlands)
Global warming entered the political agenda in the exceptionally hot summers of the late 1980s,
when environmental crusaders predicted the imminent melting of the polar ice caps, the second
Flood, and maybe an end to life on Earth from a ‘runaway greenhouse effect’ caused by man’s
emissions of greenhouse gases. Vice-president Albert Gore even dubbed the summer of 1988 the
‘Kristallnacht before the warming holocaust’. Particularly the steady increase in the atmospheric
concentration of carbon dioxide from man’s agricultural activities and large-scale burning of fossil
fuels was
indicted as the main evildoer. The press, ever eager for apocalyptic predictions, gave extensive
coverage, so that much of the public was taken in by it all. The greenhouse warming protagonists
grossly exaggerated their claims in order to
convince the public and politicians of the validity of their doomsday scenarios – a policy illustrated
by the notorious statement by the climatologist Stephen H. Schneider, adviser to vice-president
Albert Gore, that
To do that [reduce the risk of potentially disastrous climatic change] we have to get some broadbased support, to capture the public’s imagination. That, of course, entails getting loads of media
coverage. So we have to offer up scary scenarios, make simplified dramatic statements, and make
little mention of any doubts we might have.
(Discover Magazine, October 1989).
No wonder that the predictions of the imminent greenhouse catastrophe were met with reservation
in the world of science. The scary scenarios rely on computer models that attempt to quantify
mathematically the multitude of phyisical, chemical, biological and geological factors, both
natural and man-made, that play a role in the climate system. Such models are necessarily
reductionistic and deterministic. Many climate forcing factors and feedbacks are not or
incompletely understood – for example the roles of clouds, the biosphere, and the most important
natural greenhouse gas: water vapour. The different factors influential in climate change also
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operate at varying scales of time and space and are extremely complex, even when they function
by themselves. When they act together, or are coupled, the
complications multiply greatly. The models have to cope with numerous feedbacks simultaneously.
Climate is a non-linear, ‘chaotic’ system, and small changes in one factor can produce large, but
unpredictable changes in the result. The long-term forecasts by the computer models represent
essentially a ‘virtual reality’.
This is now also recognized by James Hansen from NASA’s Goddard Institute. In 1988 he initiated
the greenhouse warming doomsday scenario with his testimony to the U.S. Senate Committee on
Energy and Natural Resources, but in 1997 he and 42 co-authors stated that
Scientists and lay persons have a predilection for deterministic explanations of climatic variations.
However, climate can vary chaotically, i.e., in the absence of any forcing. The slightest alteration of
initial or boundary conditions changes the developing patterns, and thus next year’s weather in an
inherently unpredictable way. This behavior results from the non-linear fundamental equations
governing the
dynamics of such a system.
(Journ. Geoph. Res. 102, D.22, 25,679-25,720, November 1997).
This paper, reporting about experiments with three major computer models, shows that climate is
chaotic at all scales and thus effects of long-term forcings, such as a changing concentration of
greenhouse gases, are essentially unpredictable.
However, particularly among geologists, even more scepticism exists about the indictment of
atmospheric carbon dioxide as a dominant climate forcing factor. For geologists, climate is a
manifestation of how the incoming energy from the Sun
is absorbed, redistributed by air and oceans, and eventually re-radiated to space as long-wave
radiation. The outcome is determined by many interacting and in part interrelated and
interdependent processes, involving the incoming solar radiation, the atmosphere (including the
warming by greenhouse gases), the hydrosphere (particularly the oceans), the biosphere, the surface
of the crust, and soils on land. The geologic record shows that all components of this system are in
constant motion and continual change. Continuous climate change is thus a normal phenomenon
in Earth’s history. Nevertheless, in spite of the steadily increasing heat output from the Sun, Earth
managed to maintain air temperatures within a narrow range throughout the four billion years of
recorded geologic history.
Of course, the greenhouse gases in the atmosphere, including carbon dioxide, do play a role in the
climate system. They trap infrared radiation from the ground, thus keeping the surface air
warmer than it would otherwise be. This natural ‘greenhouse blanket’ has been in operation for
billions of years and is an important factor in making our planet a fit place for life.
But are changes in the concentration of carbon dioxide really such a major factor in bringing about
climatic change? Does there exist a simple cause-and-effect relationship between changes in the
atmospheric concentration of carbon dioxide
and global temperature change? Does the enhanced greenhouse effect due to man’s injection of
carbon dioxide warrants the alarm for an imminent calamitous climatic warming? Evidence from
the historical and geological record does not lend support to such a governing role of atmospheric
carbon dioxide as a climate forcing factor.
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The concentration of carbon dioxide in the atmosphere is determined by a global system of supply
and extraction. On the one side there is a continuous addition through degassing of the solid Earth,
mainly by volcanoes and mid-ocean ridges,
while on the other side there is a continuous removal through biological, chemical and geological
processes. The volatiles exhaled by volcanoes include about 80 percent water, 20 percent carbon
dioxide, and minor amounts of a wide variety of other components. The emanated water vapour
condenses at the saturation point and adds to the oceans, but most of the exhaled carbon dioxide
would accumulate if it were not continuously pulled from the air by three natural ‘pumps’.
Two of these, the ‘carbonation pump’ (chemical weathering enhanced by bacterial activity) and the
‘carbonate pump’ (biological precipitation of carbonate in the oceans) lead eventually to the storage
of carbon dioxide in enormous
deposits of limestone and other carbonate rocks.
The third, the ‘biomass pump’ (photosynthesis, followed by the burial of organic matter in
sediments), produces deposits of fossil hydrocarbons, coal, peat and dispersed biogenic carbon in
sediments. If all that carbon had not been removed,
the carbon dioxide pressure at Earth’s surface today would amount to about 70 bars, some 200,000
times the present value. Our atmosphere would then resemble very much that of Venus – both
planets posess a similar amount of carbon dioxide on or near the surface, but whereas on Venus it is
a constituent of the atmosphere, on Earth most of it is stored in sediments. Still, all carbon in
sediments, biosphere, atmosphere and oceans is only a tiny fraction of the total amount of carbon in
the Earth. Most of it occurs in core and mantle – from this reservoir stems the juvenile carbon
dioxide in
volcanic exhalations.
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Over the last century there also is a substantial anthropogenic input through industrial activities and
changes in land use. Since 1958, when continuous monitoring started, the atmospheric
concentration of carbon dioxide has grown from 315 ppmv to the present 368 ppmv, a rise
largely attributed to man-made emissions. As earlier air analyses are subject to uncertainty, air
bubbles trapped in glacier ice that formed when snow fell on Antarctica and Greenland are
usually taken
as the best estimates of the concentrations of carbon dioxide and other greenhouse gases
before 1958. They indicate that the atmospheric carbon dioxide level has been rising from a preindustrial level of 280 ppmv. The increase was slow
until about 1900, but has accelerated dramatically during the twentieth century. Going further back
in time, the bubbles indicate a growth since the last glacial minimum, some 15,000 years ago, from
an initial level of about 190 ppmv to the pre-industrial level of 280 ppmv. The growth was not
steadily, but with oscillations: at times it leveled off or was even negative, while at other times it
accelerated.
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The increase from 280 to 358 ppmv in 1994 relates to an addition of 607 gigatons CO2, but the
cumulative release from fossil fuel burning, cement manufacturing and the oxidation of organic
matter exposed by the tilting of soils and deforestation has been estimated by IPCC at about 1,166
gigatons. Natural processes have thus already removed nearly half of this cumulated input through
the absorption by ocean water, living organisms (mostly forests in the boreal and temperate zones
and plankton in the oceans), and one or more unidentified sinks. Though it has so far been assumed
that
most of the excess atmospheric CO2 would be removed over about a century, the biologicalgeological control system is – at a higher CO2 level causing higher sink flows – able to respond
even quite faster in counteracting a rise in atmospheric carbon dioxide. Within 30 years about 4060% of the CO2 currently released to the atmosphere is removed (IPCC, 1995).
A crucial question is: do the air bubbles in glacier ice really always reflect the atmospheric
composition during precipitation? There is reason to doubt this. Some investigators have argued that
a selective uptake of carbon dioxide in the crystal lattice may cause fractionation of the gases in the
bubbles, leading with time in an unpredictable way to a change of the carbon dioxide concentration.
This finds support in the fact that the carbon dioxide values obtained when the whole ice sample is
vaporized, are usually higher than those from the air that is liberated when the ice is grinded or
abrased – the conventional practice in analysing the air bubbles. Also, studies in the palaeobotanical
laboratory of Utrecht University show that the stomatal indices of leaves grown between 11,500 and
10,500 years ago, at the end of the last glaciation, indicate atmospheric carbon dioxide
concentrations considerably higher than the values obtained from bubbles in ice.
Nevertheless, there can be little doubt that considerable fluctuations in the atmospheric carbon
dioxide concentration did occur in the time interval covered by the ice cores. In addition, the
oxygen isotope composition of the ice reflects fluctuations in the global temperature during the
precipitation of the snow that in time conversed to the glacial ice. The fluctuations in the carbon
dioxide concentration appear to track those in temperature to a remarkable degree, but a closer look
reveals that the fluctuations generally leg behind those in temperature. Never does a changing
carbon dioxide concentration precede that of temperature. This pattern can be explained by release
of carbon dioxide from the oceans during warming and solution during cooling. A changing carbon
dioxide concentration was thus not the cause of the change in temperature, but could have amplified
it in a positive feedback.
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For the last century, the available temperature data indicate a global warming of about 0.5
degrees centigrade, but this rise is not undisputed. It is deduced from measurements by a
network of ground-based stations, where urban and industrial heating contaminates the
record, while data are lacking from many remote areas, including the oceans. Although care is
taken to overcome these disturbing factors, it remains speculative to derive from this temperature
record something like the ‘mean global temperature’. Moreover, a warming trend of the lower
atmosphere seems to be at odds with measurements since 1979 by orbiting satellites of microwave
emissions from oxygen molecules, which allows the determination of their temperature to an
accuracy of 0.01 degree centigrade. These data are confirmed by measurements
from weather balloons and do not show a warming trend, rather a slight cooling.
Still, retreating glaciers, shifting latitudinal vegetation zones and other circumstantial evidence do
point to an increase in global temperatures over the last century. Ardent greenhouse advocates insist
that this is clear evidence of the enhanced greenhouse warming due to the steadily rising
concentration of atmospheric greenhouse gases, particularly carbon dioxide. However, a warming
of the order of 0.5 degrees lies well within the observed natural short-term variability in the past,
but far beneath the enhanced greenhouse warming that, according to the climate models, the added
carbon dioxide should have invoked. Moreover, much of the warming was already realised before
1940, when only 30 percent of the increase in atmospheric carbon dioxide over the last two
centuries has taken place. Finally, the warming has been far
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from steady. Between 1940 and 1970 there even was a transient cooling, which led some
climatologists in the 1970s to claims that an ice age is imminent. This period of cooling is
difficult to reconcile with the role attributed to carbon dioxide
as the dominant climate forcing factor, as there was not any interruption in the ever-rising level of
carbon dioxide. Nor was there an increase in volcanic activity that could have caused a transient
cooling by putting a veil of dust into the stratosphere.
Going back in time, the last millennia are characterised by a succession of cool and warm
periods, until the steep drop when approaching the end of the last Ice Age about 10,000 years ago.
A fairly detailed picture of annual and decade-to-decade variations in global temperature is
emerging from studies of historical records, ice cores, tree rings, and growth rings of corals.
There were several long cold spells, for example the famous ‘Little Ice Age’ in the seventeenth
century. A well-known warm spell was the ‘Medieval Warm Period’, which lured Vikings into
colonising Greenland. None of these climatic changes shows a clear correlation with changes in
atmospheric carbon dioxide.
During most of the four billion years of recorded Earth’s history, warmer conditions than today
prevailed, with no or only small polar ice caps. These overall warm conditions were interrupted by
five cold spells, each lasting millions of years,
during which the polar ice caps expanded. For the last three million years or so Earth has been in
such a cold spell, but
the extent of the polar ice caps varies through time: the ice sheets advance down to the lower
latitudes during glaciations, and retreat again during interglacial stages. The rhythmic fluctuations
appear to be governed by periodic changes over time scales of thousands of years in the orbit of the
Earth around the Sun, the tilt of Earth’s axis, and the wobble of Earth’s spin axis. This cyclic
astronomical climate forcing is operating all over Earth’s history – it is not only reflected in the
advances and retreats of the polar ice sheets, but also in sedimentary sequences throughout the
whole of geologic
time.
When penetrating deeper into the past the geological record reveals numerous fluctuations in both
global temperature
and atmospheric carbon dioxide, sometimes correlated and sometimes not. For example, in the
Middle Pliocene,
3.0-3.5 million years ago, when the Earth’s surface did not much differ from today’s, it was
globally much warmer than at present. Still, the stomata of fossil leaves reveal that the carbon
dioxide level at that time was about the same as now, whereas, according to the climate models, the
level should have been at least twice that of today if this gas would be the prime arbiter of global
temperature.
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For the Middle Cretaceous, about 100-120 million years ago, the sedimentary record indicates
that the air contained some eight times as much carbon dioxide as today, probably due to the
enormous volcanic activity in the Pacific region. Because of the outflow of massive volumes of
basaltic lava at the Pacific Ocean floor the sea level was higher and the dry land area smaller than
today. The land surface had little relief, so there was little removal of carbon dioxide through
weathering. On the other hand, the enormous limestone deposits from this period testify that the
biological ‘carbonate pump’ was working at full capacity. The sedimentary record indicates a
warmer climate than today, but much less than the climate models dictate for such a high carbon
dioxide pressure. The warmer climate can to some extent be attributed to Earth’s lower albedo
because of the greater area covered by sea. Oxygen isotopes show that the tropics were about six to
seven degrees centigrade cooler than today, while polar temperatures were about 13 degrees colder
than the
tropics, less than half the modern difference. The Mid Cretaceous was thus primarily characterised
by a rather flat
latitudinal temperature gradient, probably because the low relief of the continents allowed an
unimpeded heat transfer
from the tropics to the poles.
Further back in time sediments from the Late Ordovician show that 450 million years ago the
atmosphere contained even some 16 times more carbon dioxide than today. Still, this was not
accompanied by unusual warm temperatures. On the
contrary, at higher latitudes there was widespread glaciation. The average global temperature did
not much differ from today’s.
There are, of course, many environmental differences between the geological past and the present,
the more so when going further back in time. Nevertheless, the geological record clearly shows that
the climate models are not able to reproduce past climates realistically, if carbon dioxide is taken as
a major factor in climate regulation. This casts doubt on the assumption that changes in atmospheric
carbon dioxide should be a basic driver of global temperature change. Obviously, the temperature
effect of such a change is arrested by a host of competing feedbacks.
If not carbon dioxide, what other natural factors may have enforced the climatic changes in the
past? On time-scales of millions of years the surface expression of plate-tectonic processes must
have been important, but these cannot play a significant role in forcing climatic changes over
decades or centuries. Among earth scientists it is a long-held suspicion that changes in the
behaviour of the Sun are in some way responsible. For example, historical records report that
the coldest epoch in the ‘Little Ice Age’ coincided with a prolonged period when sunspots
were almost absent. The global cooling between 1940 and 1970 also coincided with a period of
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low sunspot activity. Further back in time, a relation between the sunspot cycle and climate change
is shown by high-resolution sedimentary sequences such as those covering the last 13,000 years in
the maars of the Eifel – they display a rhythmic climatic fluctuation with an average period of
eleven years.
A relationship between solar activity and Earth’s climate is also apparent from isotope studies of
tree rings and ice core samples. Tree rings high in carbon-14 grew and snow high in beryllium10 precipitated when the climate was cool, and vice versa. Both radioactive isotopes are
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produced by cosmic rays entering the Earth’s tmosphere. During periods of increased sunspot
activity, the magnetic fields in the solar wind have a larger shielding effect on cosmic rays,
preventing them from entering and thus causing a reduced cloud coverage. Carbon-14 is taken up in
growing trees and beryllium-10 in precipitating snow. Their abundances in tree rings and ice cores,
respectively, reflect the solar activity during growth and precipitation over the past 8,000 and
100,000 years.
How changes in the solar activity drive changes in Earth’s climate system, is still a matter of debate.
Anyhow, the close match between changes in the length of the sunspot cycle and mean
temperatures on land in the northern hemisphere, is a
clear sign that changes in the climate over the past century were mainly governed by changes in the
Sun’s activity. This excellent correlation contrasts sharply with the poor correlation between the
steadily increasing carbon dioxide level and
the average global temperature.
Even James Hansen from NASA’s Goddard Institute no longer considers the emission of carbon
dioxide as a major factor in bringing about the apparent surface heating in our time. (PNAS 15
Aug 2000) He now attributes the biggest role to the emission of black carbon (soot) and
greenhouse gases other than carbon dioxide, particularly tropospheric ozone, methane and
chlorofluorocarbons (CFCs) – the CO2 effect itself being mostly compensated by aerosols.
However, man’s industrial and agricultural activities emit not only greenhouse gases such as
carbon dioxide, ozone, nitrous oxide and methane that are added to the natural reservoirs and
join in the global biological and geochemical cycles, but also pollutants that are alien to
Earth’s environment. Some have an exceptionally large infrared absorption. For example, the
current atmosphere contains very small amounts of a number of long-lived fluor compounds of
exclusively anthropogenic origin*, with a warming potential up to tens of thousands of times larger
than carbon dioxide. They did not occur before their invention and industrial production in the 20th
century, but are building up since then at an accelerating rate. Their cumulative radiative forcing
has not yet been evaluated properly.
However, humankind influences the climate system above all, at first on a regional scale, through
the disruption of the natural interaction between land surface, atmosphere and biosphere. For
example, through the large-scale destruction of
tropical forests, overgrazing, soil erosion, desertification, changes in land use through agriculture
and urbanization, urban heat production, industrial emission of aerosols, construction of storage
lakes and other changes in the surface water cycle, pollution, and so on. All these disruptions of the
natural environmental system increase in our time at an alarming rate as the inevitable consequence
of the rapidly growing world population, accompanied by an ever rising level of consumption.
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Over the last decade the insight in the climate system has grown. The advocates of the greenhouse
warming were forced to water down their initial predictions from an average global warming of
some five degrees centigrade by the end of the 21st century to about one to two degrees, and from a
sea level rise of up to eight metres to about half a metre. However, pressure groups of
environmentalists, supported by a number of climatologists who claim to speak for all relevant
science, had already managed to command the attention of governments and media. They
succeeded in bringing about international commitments to curb the emissions of carbon dioxide.
Although this may be seen as a case of man’s neurotic capacity to worry about the wrong things,
there still are excellent reasons otherthan the dreaded climatic
warming for such a reduction. The reserves of fossil fuels are not inexhaustible, so their use should
anyhow be economised. Mankind will also benefit from planting more trees than there are felled.
Moreover, many scientists who are sceptical about the validity of the greenhouse warming scenario,
even so do support measures to curb the emission of carbon dioxide on the basis of the so-called
‘Precautionary Principle’: prevent any action that might have serious consequences, how
improbable they may be.
But there never was and is anything like a ‘scientific consensus’ on which the policy makers based
their commitments. On the contrary, the initial claim that the man-made emission of carbon dioxide
would lead to a calamitous global warming, is increasingly contested, both on methodological
grounds and on the basis of data from the real world. In ordinary scientific discourse the adverse
evidence produced by a single researcher is sufficient to destroy any cherished theory – when in
Nazi Germany a bunch of scientists put forward their consensus rejection of the ‘Jewish doctrine’ of
relativity in the ill-famed book Hundert gegen Einstein, the master in Princeton replied ironically
that one would have been enough. But, unfortunately, the greenhouse warming scenario has been
seized upon and made to a political issue
by environmental interest groups, no longer subject to scientific scrutiny.
_______________
For example: chlorofluorocarbons, CFCs; hydrofluorocarbons, HFCs;sulfur fluoride, SF6;
trifuoromethyl sulfur pentafluoride, SF5CF 3.
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15 September 2000, Prof. Dr. Harry N. A. Priem
Email: [email protected]
Fax: 0031-20-5233410 Phone: 0031-20-6766386
This paper: http://www.ozemail.com.au/~hughesw7/hpriem.htm
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