There Has Been No Global Warming
for the Past 70 Years
Volume 3, Number 13: 1 July 2000
(See more articles on the subject in: CO2science.org/
In our editorial
of 15 June 2000 - The Global Surface Air Temperature Record Must Be Wrong -
we reviewed a large body of evidence that suggests that the highly-hyped "unprecedented
global warming" of the past two decades never actually occurred.
This evidence includes (1) the satellite microwave-sounding-unit temperature
record, which in the absence of the massive 1998 El Niño heat pulse shows
no warming whatsoever from 1979 to the present, (2) the weather-balloon temperature
record, which for the same circumstances also shows no warming, (3) the surface-
and satellite-derived temperature records of earth's polar regions, which also
show no warming, and (4) the high-quality U.S. Historical Climatology Network
data base, which, not surprisingly, also shows no statistically significant
warming over this period. We now augment this substantial body of empirical
evidence for no global warming over the last two decades with observations gleaned
from tree-ring reconstructions of surface air temperature.
If you want to contribute with our work, sending no money,
First, there is the growing-season temperature history of the entire northern
boreal forest region, which has been published most recently in the review of
Briffa (2000) and is referred to by him as "the
best overall indicator to date of long-term temperature changes over the higher
northern land areas." Derived from a large number of tree-ring
density chronologies obtained from some 400 sites in the western United States,
Canada, Europe, Fennoscandia and northern Siberia, this temperature record shows
a dramatic departure from the instrumental temperature record over the last
70 years, with the instrumental record depicting unprecedented 20th century
warming, but with the tree-ring record showing nothing of the sort. And the
reason for the discrepancy? In the words of Briffa, "the reason is not
known." We, however, believe that the reason should be obvious: the instrumental
temperature record is simply wrong.
Second, there is the somewhat contradictory story told by a number of temperature
reconstructions derived from tree-ring width chronologies. As Briffa (2000)
recounts it, tree-growth, as represented in various standardized tree-ring chronologies
in various parts of the world, often seems anomalous in the 20th century as
compared to earlier centuries. "This widespread
anomaly is extremely important, for he notes that "the recent high growth
rates . . . provide major pieces of evidence being used to assemble a case for
anomalous global warming, interpreted by many as evidence of anthropogenic activity,"
specifically mentioning Mann et al. (1998, 1999) in this regard. But as Briffa
further notes, the empirically derived regression equations upon which the temperature
reconstructions are based may be compromised if the growth rates of earth's
trees have been substantially enhanced over the past century or so by some other
global environmental influence that has increasingly manifested itself over
the same time period.
What might this influence - if it exists - be? Briffa cites a number of possibilities,
including the historical rise in the air's CO2 content over this period and
a number of plant physiological processes that become increasingly more efficient
in response to this phenomenon; and he explains how this influence could act
in opposition to the declining tree-ring density phenomenon described in the
preceding paragraph. Indeed, LaMarche et al. (1984) and Graybill and Idso (1993)
demonstrated several years ago that the historical rise in the air's CO2 content
could readily explain the anomalous 20th century growth spurt in tree-ring width
expansion; and Briffa states that "widespread evidence is accumulating
of 'enhanced' productivity (ring-width, basal area and wood mass) in the 19th
and 20th centuries, similar to positive growth trends observed in earlier studies,"
that is, in the studies of LaMarche et al. and Graybill and Idso.
It's essentially a no-brainer. Enhanced tree growth induced by the historical
rise in the air's CO2 content - possibly augmented by enhanced nitrogen deposition
(Idso, 1995) - has been increasing the growth rates of trees all around the
world for over a century or more (see, for example, our editorials of 15 April
1999 and 1 April 2000: Atmospheric CO2 Enrichment: Boon or Bane of the Biosphere?
and The Future of Forests). Furthermore, this growth enhancement has been accelerating
over time (Phillips and Gentry, 1994); and it is this ever-intensifying biological
phenomenon that some are using to bolster their claim that the climate is warming
at an ever-increasing rate. Nothing, however, could be further from the truth.
For the past two decades at least, and possibly for the past seven decades,
earth's true surface air temperature has likely experienced no net change.
This latter conclusion may sound incredulous to some; but it follows directly
from the likely fact that there has been no net warming from 1979 to 2000, as
we indicated in our editorial of 15 June 2000, plus the fact that even the contaminated
surface air temperature records depict no warming (they actually show a cooling!)
from 1930 to 1979, as can be verified by visiting the World Temperatures section
of our website and computing the surface air temperature trend from 1930 to
1979 from both the Global Historical Climatology Network and the Jones et al.
In view of the extreme likelihood that there has thus been no net warming of
the planet over the past 70 years, during which time the vast majority of all
anthropogenically-produced CO2 has been emitted to the atmosphere, we conclude
that since there should have been a sizeable CO2-induced increase in atmospheric
radiative forcing over this period, there must have been a suite of compensatory
negative feedbacks that totally overwhelmed the standard "greenhouse"
impetus for warming (see our Position Paper on Carbon Dioxide and Global Warming:
Where We Stand on the Issue). Hence, there would appear to be absolutely no
foundation in factual data of any sort for supposing that any further man-induced
increases in the air's CO2 content would warm the planet either.
Dr. Craig D. Idso
President Dr. Keith E. Idso
Briffa, K.R. 2000. Annual climate variability in the Holocene: Interpreting
the message of ancient trees. Quaternary Science Reviews 19: 87-105.
Graybill, D.A. and Idso, S.B. 1993. Detecting the aerial fertilization effect
of atmospheric CO2 enrichment in tree-ring chronologies. Global Biogeochemical
Cycles 7: 81-95.
Idso, S.B. 1995. CO2 and the Biosphere: The Incredible Legacy of the Industrial
Revolution. Third Annual Kuehnast Lecture. Department of Soil, Water and Climate,
University of Minnesota, St. Paul, MN.
LaMarche Jr., V.C., Graybill, D.A., Fritts, H.C. and Rose, M.R. 1984. Increasing
atmospheric carbon dioxide: Tree ring evidence for growth enhancement in natural
vegetation. Science 225: 1019-1021.
Mann, M.E., Bradley, R.S. and Hughes, M.K. 1998. Global scale temperature patterns
and climate forcing over the past six centuries. Nature 392: 779-787.
Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures
during the past millennium: Inferences, uncertainties and limitations. Geophysical
Research Letters 26: 759-762.
Phillips, O.L. and Gentry, A.H. 1994. Increasing turnover through time in tropical
forests. Science 263: 954-958.
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