Scientists conclude there are no harmful environmental effects
of increased atmospheric carbon dioxide
ARTHUR B. ROBINSON, SALLIE L. BALIUNAS, WILLIE SOON, AND ZACHARY W. ROBINSON
Oregon Institute of Science and Medicine, 2251 Dick George Rd., Cave Junction, Oregon 97523 email@example.com
George C. Marshall Institute, 1730 K St., NW, Ste 905, Washington, DC 20006 firstname.lastname@example.org January 1998
A review of the research literature concerning the environmental consequences of increased levels of atmospheric carbon dioxide leads to the conclusion that increases during the 20th Century have produced no deleterious effects upon global weather, climate, or temperature. Increased carbon dioxide has, however, markedly increased plant growth rates. Predictions of harmful climatic effects due to future increases in minor greenhouse gases like CO2 are in error and do not conform to current experimental knowledge.
World leaders gathered in Kyoto, Japan, in December 1997 to consider
a world treaty restricting emissions of ''greenhouse gases,'' chiefly
carbon dioxide (CO2), that are thought to cause ''global warming''
severe increases in Earth's atmospheric and surface temperatures,
with disastrous environmental consequences. Predictions of global
warming are based on computer climate modeling, a branch of science
still in its infancy. The empirical evidence actual measurements of
Earth's temperature shows no man-made warming trend. Indeed, over
the past two decades, when CO2 levels have been at their highest,
global average temperatures have actually cooled slightly.
The concentration of CO2 in Earth's atmosphere has increased during the past century, as shown in figure 1 (1).
To put these figures in perspective, it is estimated that the atmosphere contains 750 Gt C; the surface ocean contains 1,000 Gt C; vegetation, soils, and detritus contain 2,200 Gt C; and the intermediate and deep oceans contain 38,000 Gt C (3). Each year, the surface ocean and atmosphere exchange an estimated 90 Gt C; vegetation and the atmosphere, 60 Gt C; marine biota and the surface ocean, 50 Gt C; and the surface ocean and the intermediate and deep oceans, 100 Gt C (3).
Figure 2: Surface temperatures in the Sargasso Sea (with time resolution
of about 50 years) ending in 1975 as determined by isotope ratios
of marine organism remains in sediment at the bottom of the sea (7).
The horizontal line is the average temperature for this 3,000 year
period. The Little Ice Age and Medieval Climate Optimum were naturally
occurring, extended intervals of climate departures from the mean.
The current increase in carbon dioxide follows a 300-year warming trend: Surface and atmospheric temperatures have been recovering from an unusually cold period known as the Little Ice Age. The observed increases are of a magnitude that can, for example, be explained by oceans giving off gases naturally as temperatures rise. Indeed, recent carbon dioxide rises have shown a tendency to follow rather than lead global temperature increases (6).
There is, however, a widely believed hypothesis that the 3 Gt C per year rise in atmospheric carbon dioxide is the result of the 5.5 Gt C per year release of carbon dioxide from human activities. This hypothesis is reasonable, since the magnitudes of human release and atmospheric rise are comparable, and the atmospheric rise has occurred contemporaneously with the increase in production of CO2 from human activities since the Industrial Revolution.
Figure 3: Moving 11-year average of terrestrial Northern Hemisphere peratures as deviations in ºC from the 1951-1970 mean left axis and darker line (8,9). Solar magnetic cycle lengths right axis and lighter line (10). The shorter the magnetic cycle length, the more active, and hence brighter, the sun.
In any case, what effect is the rise in CO2 having upon the global environment? The temperature of the Earth varies naturally over a wide range. Figure 2 summarizes, for example, surface temperatures in the Sargaso Sea (a region of the Atlantic Ocean) during the past 3,000 years (7). Sea surface temperatures at this location have varied over a range of about 3.6 degrees Celsius (ºC) during the past 3,000 years. Trends in these data correspond to similar features that are known from the historical record.
What causes such variations in Earth's temperature? The answer may be fluctuations in solar activity. Figure 3 shows the period of warming from the Little Ice Age in greater detail by means of an 11-year moving average of surface temperatures in the Northern Hemisphere (10). Also shown are solar magnetic cycle lengths for the same period. It is clear that even relatively short, half-century-long fluctuations in temperature correlate well with variations in solar activity. When the cycles are short, the sun is more active, hence brighter; and the Earth is warmer. These variations in the activity of the sun are typical of stars close in mass and age to the sun (13).
Figure 4 shows the annual average temperatures of the United States as compiled by the National Climate Data Center (12). The most recent upward temperature fluctuation from the Little Ice Age (between 1900 and 1940), as shown in the Northern Hemisphere record of figure 3, is also evident in this record of U.S. temperatures. These temperatures are now near average for the past 103 years, with 1996 and 1997 having been the 42nd and 60th coolest years.
Figure 5: Radiosonde balloon station measurements of global lower
tropospheric temperatures at 63 stations between latitudes 90 N and
90 S from 1958 to 1996 (15). Temperatures are three-month averages
and are graphed as deviations from the mean temperature for 1979 to
1996. Linear trend line for 1979 to 1996 is shown. The slope is minus
0.060 ºC per decade.
Figure 6: Satellite Microwave Sounding Unit, MSU, measurements of global lower tropospheric temperatures between latitudes 83 N and 83 S from 1979 to 1997 (17,18). Temperatures are monthly averages and are graphed as deviations from the mean temperature for 1979 to 1996. Linear trend line for 1979 to 1997 is shown. The slope of this line is minus 0.047 ºC per decade. This record of measurements began in 1979.
Figure 7 shows the satellite data from figure 6 superimposed upon the weather balloon data from figure 5. The agreement of the two sets of data, collected with completely independent methods of measurement, verifies their precision. This agreement has been shown rigorously by extensive analysis (19, 20).
While tropospheric temperatures have trended downward during the past 19 years by about 0.05 ºC per decade, it has been reported that global surface temperatures trended upward by about 0.1 ºC per decade (21, 22). In contrast to tropospheric temperatures, however, surface temperatures are subject to large uncertainties for several reasons, including the urban heat island effect (illustrated below).
During the past 10 years, U.S. surface temperatures have trended downward by minus 0.08 ºC per decade (12) while global surface temperatures are reported increased by plus 0.03 ºC per decade (23). The corresponding weather-balloon and satellite tropospheric 10-year trends are minus 0.4 ºC and minus 0.3 ºC per decade, respectively.
Figure 8: Tropospheric temperature measurements by satellite MSU
for North America between 30º to 70º N and 75º to 125º
W (dark line) (17, 18) compared with the surface record for this same
region (light line) (24), both plotted with 12-month smoothing and
graphed as deviations from their means for 1979 to 1996. The slope
of the satellite MSU trend line is minus 0.01 ºC per decade,
while that for the surface trend line is plus 0.07 ºC per decade.
The correlation coefficient for the unsmoothed monthly data in the
two sets is 0.92.
In North America, the atmospheric and surface records partly agree (20 and figure 8). Even there, however, the atmospheric trend is minus 0.01 per decade, while the surface trend is plus 0.07 ºC per decade. The satellite record, with uniform and better sampling, ismuch more reliable.
The computer models on which forecasts of global warming are based predict that tropospheric temperatures will rise at least as much as surface temperatures (14). Because of this, and because these temperatures can be accurately measured without confusion by complicated effects in the surface record, these are the temperatures of greatest interest. The global trend shown in figures 5, 6 and 7 provides a definitive means of testing the validity of the global warming hypothesis.
Figure 9: Qualitative illustration of greenhouse warming. Present: the current greenhouse effect from all atmospheric phenomena. Radiative effect of CO2: added greenhouse radiative effect from doubling CO2 without consideration of other atmospheric components. Hypothesis 1 IPCC: hypothetical amplification effect assumed by IPCC. Hypothesis 2: hypothetical moderation effect.
There is such a thing as the greenhouse effect. Greenhouse gases
such as H2O and CO2 in the Earth's atmosphere decrease the escape
of terrestrial thermal infrared radiation. Increasing CO2, therefore,
effectively increases radiative energy input to the Earth. But what
happens to this radiative input is complex: It is redistributed, both
vertically and horizontally, by various physical processes, including
advection, convection, and diffusion in the atmosphere and ocean.
The hypothesis of a large atmospheric temperature increase from greenhouse gases (GHGs), and further hypotheses that temperature increases will lead to flooding, increases in storm activity, and catastrophic world-wide climatological changes have come to be known as ''global warming'' a phenomenon claimed to be so dangerous that it makes necessary a dramatic reduction in world energy use and a severe program of international rationing of technology (29).
Figure 10: The radiative greenhouse effect of doubling the concentration
of atmospheric CO2 (right bar) as compared with four of the uncertainties
in the computer climate models (14, 28).
Figure 11 compares the trend in atmospheric temperatures predicted by computer models adopted by the IPCC with that actually observed during the past 19 years those years in which the highest atmospheric concentrations of CO2 and other GHGs have occurred.
In effect, an experiment has been performed on the Earth during the past half-century an experiment that includes all of the complex factors and feedback effects that determine the Earth's temperature and climate. Since 1940, atmospheric GHGs have risen substantially. Yet atmospheric temperatures have not risen. In fact, during the 19 years with the highest atmospheric levels of CO2 and other GHGs, temperatures have fallen.
Not only has the global warming hypothesis failed the experimental test; it is theoretically flawed as well. It can reasonably be argued that cooling from negative physical and biological feedbacks to GHGs will nullify the initial temperature rise (26, 30).
The reasons for this failure of the computer climate models are subjects of scientific debate. For example, water vapor is the largest contributor to the overall greenhouse effect (31). It has been suggested that the computer climate models treat feedbacks related to water vapor incorrectly (27, 32).
The global warming hypothesis is not based upon the radiative properties of the GHGs themselves. It is based entirely upon a small initial increase in temperature caused by GHGs and a large theoretical amplification of that temperature change. Any comparable temperature increase from another cause would produce the same outcome from the calculations.
At present, science does not have comprehensive quantitative knowledge about the Earth's atmosphere. Very few of the relevant parameters are known with enough rigor to permit reliable theoretical calculations. Each hypothesis must be judged by empirical results. The global warming hypothesis has been thoroughly evaluated. It does not agree with the data and is, therefore, not validated.
Figure 12: Eleven-year moving average of global surface temperature,
as estimated by NASA GISS (23, 33, and 34), plotted as deviation from
1890 (left axis and light line), as compared with atmospheric CO2
(right axis and dark line) (2). Approximately 82% of the increase
in CO2 occurred after the temperature maximum in 1940, as is shown
in figure 1.
Aside from computer calculations, two sorts of evidence have been
advanced in support of the ''global warming'' hypothesis: temperature
compilations and statements about global flooding and weather disruptions.
Figure 12 shows the global temperature graph that has been compiled
by National Aeronautic and Space Administration's Goddard Institute
of Space Studies (NASA GISS) (23, 33, and 34). This compilation, which
is shown widely in the press, does not agree with the atmospheric
record because surface records have substantial uncertainties (36).
Figure 13 illustrates part of the reason.
Figure 13: Surface temperature trends for the period of 1940 to 1996
from 107 measuring stations in 49 California counties (39, 40). After
averaging the means of the trends in each county, counties of similar
population were bined and plotted as closed circles along with the
standard errors of their means. The six measuring stations in Los
Angeles County were used to calculate the standard error of that county,
which is plotted alone at the county population of 8.9 million. The
''urban heat island effect'' on surface ments is evident. The straight
line is a least-squares fit to the closed circles. The points marked
''X'' are the six unadjusted station records selected by NASA GISS
(23, 33, and 34) for use in their estimate of global temperatures
as shown in figure 12.
In addition, incomplete regional temperature records have been used to support ''global warming.'' Figure 14 shows an example of this, in which a partial record was used in an attempt to confirm computer climate model predictions of temperature increases from green-house gases (41). A more complete record refuted this attempt (42).
Not one of the temperature graphs shown in figures 4 to 7, which include the most accurate and reliable surface and atmospheric temperature measurements available, both global and regional, shows any warming whatever that can be attributed to increases in green-house gases. Moreover, these data show that present day temperatures are not at all unusual compared with natural variability, nor are they changing in any unusual way.
Figure 14: The solid circles in the oval are tropospheric temperatures for the Southern Hemisphere between latitudes 30 S and 60 S, published in 1996 (41) in support of computer-model-projected warming. Later in 1996, the study was refuted by a longer set of data, as shown by the open circles (42).
The computer climate models do not make any reliable predictions whatever concerning global flooding, storm variability, and other catastrophes that have come to be a part of the popular definition of ''global warming.'' (See Chapter 6, section 6-5 of reference 14.) Yet several scenarios of impending global catastrophe have arisen separately. One of these hypothesizes that rising sea levels will flood large areas of coastal land. Figure 15 shows satellite measurements of global sea level between 1993 and 1997 (43). The reported current global rate of rise amounts to only about plus 2 mm per year, or plus 8 inches per century, and even this estimate is probably high (43). The trends in rise and fall of sea level in various regions have a wide range of about 100 mm per year with most of the globe showing downward trends (43).
Similarly, claims that hurricane frequencies and intensities have been increasing are also inconsistent with the data. Figure 16 shows the number of severe Atlantic hurricanes per year and also the maximum wind intensities of those hurricanes. Both of these values have been decreasing with time.
Figure 16: Annual numbers of violent hurricanes and maximum attained
wind speeds during those hurricanes in the Atlantic Ocean (46). Slopes
of the trend lines are minus 0.25 hurricanes per decade and minus
0.33 meters per second maximum attained wind speed per decade.
How high will the carbon dioxide concentration of the atmosphere
ultimately rise if mankind continues to use coal, oil, and natural
gas? Since total current estimates of hydrocarbon reserves are approximately
2,000 times annual use (47), doubled human release could, over a thousand
years, ultimately be 10,000 GT C or 25% of the amount now sequestered
in the oceans. If 90% of this 10,000 GT C were absorbed by oceans
and other reservoirs, atmospheric levels would approximately double,
rising to about 600 parts per million. (This assumes that new technologies
will not supplant the use of hydrocarbons during the next 1,000 years,
a pessimistic estimate of technological advance.)
Figure 17: Standard normal deviates of tree ring widths for (a) bristlecone
pine, limber pine, and fox tail pine in the Great Basin of California,
Nevada, and Arizona and (b) bristlecone pine in Colorado (48). The
tree ring widths have been normalized so that their means are zero
and deviations from the means are displayed in units of standard deviation.
Figures 17 to 22 show examples of experimentally measured increases in the growth of plants. These examples are representative of a very large research literature on this subject (49-55). Since plant response to CO2 fertilization is nearly linear with respect to CO2 concentration over a range of a few hundred ppm, as seen for example in figures 18 and 22, it is easy to normalize experimental measurements at different levels of CO2 enrichment. This has been done in figure 23 in order to illustrate some CO2 growth enhancements calculated for the atmospheric increase of about 80 ppm that has already taken place, and that expected from a projected total increase of 320 ppm.
As figure 17 shows, long-lived (1,000- to 2000-year-old) pine trees have shown a sharp increase in growth rate during the past half-century.
Figure 18: Young Eldarica pine trees were grown for 23 months under
four CO2 concentrations and then cut down and weighed. Each point
represents an individual tree (56). Weights of tree parts are as indicated.
Figure 19: Inventories of standing hardwood and softwood timber in
the United States compiled from Forest Statistics of the United States
Figure 20: Fig. 20. Relative trunk and limb volumes and fine root
biomass of young sour orange trees; and trunk and limb volumes and
numbers of oranges produced per mature sour orange tree per year at
400 ppm CO2 (light bars) and 700 ppm CO2 (dark bars) (59, 60). The
400 ppm values were normalized to 100. The trees were planted in 1987
as one-year-old seedlings. Young trunk and limb volumes and fine root
biomass were measured in 1990. Mature trunk and limb volumes are averages
for 1991 to 1996. Orange numbers are averages for 1993 to 1997.
Figure 21: Grain yields from wheat grown under well watered and poorly
watered conditions in open field experiments (61, 62). Average CO2-induced
increases for the two years were 10% for wet and 23% for dry conditions.
While the results illustrated in figures 17-21 are remarkable, they are typical of those reported in a very large number of studies of the effect of CO2 concentration upon the growth rates of plants (49-55).
Figure 22 summarizes 279 similar experiments in which plants of various types were raised under CO2-enhanced conditions. Plants under stress from less-than-ideal conditions – a common occurrence in nature – respond more to CO2 fertilization. The selections of species shown in figure 22 were biased toward plants that respond less to CO2 fertilization than does the mixture actually covering the Earth, so figure 22 underestimates the effects of global CO2 enhancement.
Figure 23 summarizes the wheat, orange tree, and young pine tree enhancements shown in figures 21, 20, and 18 with two atmospheric CO2 increases – that which has occurred since 1800 and is believed to be the result of the Industrial Revolution and that which is projected for the next two centuries. The relative growth enhancement of trees by CO2 diminishes with age. Figure 23 shows young trees.
Clearly, the green revolution in agriculture has already benefited from CO2 fertilization; and benefits in the future will likely be spectacular. Animal life will increase proportionally as shown by studies of 51 terrestrial (63) and 22 aquatic ecosystems (64). Moreover, as shown by a study of 94 terrestrial ecosystems on all continents except Antarctica (65), species richness (biodiversity) is more positively correlated with productivity – the total quantity of plant life per acre – than with anything else.
There are no experimental data to support the hypothesis that increases
in carbon dioxide and other greenhouse gases are causing or can be
expected to cause catastrophic changes in global temperatures or weather.
To the contrary, during the 20 years with the highest carbon dioxide
levels, atmospheric temperatures have decreased.
Figure 22: Summary data from 279 published experiments in which plants
of all types were grown under paired stressed (open circles) and unstressed
(closed circles) conditions (66). There were 208, 50, and 21 sets
at 300, 600, and an average of about 1350 ppm CO2, respectively. The
plant mixture in the 279 studies was slightly biased toward plant
types that respond less to CO2 fertilization than does the actual
global mixture and therefore underestimates the expected global response.
CO2 enrichment also allows plants to grow in drier regions, further
increasing the expected global response.
As coal, oil, and natural gas are used to feed and lift from poverty vast numbers of people across the globe, more CO2 will be released into the atmosphere. This will help to maintain and improve the health, longevity, prosperity, and productivity of all people.
Human activities are believed to be responsible for the rise in CO2 level of the atmosphere. Mankind is moving the carbon in coal, oil, and natural gas from below ground to the atmosphere and surface, where it is available for conversion into living things. We are living in an increasingly lush environment of plants and animals as a result of the CO2 increase. Our children will enjoy an Earth with far more plant and animal life as that with which we now are blessed. This is a wonderful and unexpected gift from the Industrial Revolution.
Figure 23(a): and
Figure 23(b): Calculated growth rate enhancement of wheat, young
orange and very young pine trees already taking place as a result
of atmospheric enrichment by CO2 during the past two centuries (a)
and expected to take place as a result of atmospheric enrichment by
CO2 to a level of 600 ppm (b).
Keeling, C. D. and Whorf, T. P. (1997) Trends Online:
A Compendium of Data on Global Change, Carbon Dioxide Information
Analysis Center, Oak Ridge National Laboratory; [http://cdiac.esd.ornl.gov/ftp/ndp001r7/].
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