This 1990 IPCC graph shows that current temperatures are much lower than in the recent
past and thus was not alarming.
Later, the IPCC picked up Mann’s :hockey stick” (below) and suddenly the world had
a climate problem. The only problem was that the “hockey stick” had a number of serious
flaws and was quietly de-emphasized in the next IPCC report. These flaws, found by
McIntyre & McKitrick and verified by the National Academy of Sciences are outlined
World Temperature History published by the IPCC in 1990
Michael Mann’s Hockey Stick published in 1998 (And Al Gore’s too!)
The rise in temperature started just after 1900, perhaps 1910, but man’s CO2 emissions
were very small before 1950.
The “tree rings, corals and historical records” end at about 1980, while the report
was published in 2001. Where is the later data? Some critics observed that tree rings
started diverging from temperature during that time period.
The well proven, “little ice age” is missing.
The well proven “medieval warm period” is missing. (earlier IPCC reports(above) show
these features prominently, the “medieval warming” period’s temperature being greater
The above graph first appeared in Nature 392: 779-787 . It was criticized by Steve
McIntyre etal in several papers: mcintyre 2005 , the criticism was mentioned in
several papers WSJ and explained by Ross Mckitrick. Finally a congressional hearing
which requested the National Academy of sciences to study the claims and counter
claims. Two reports resulted, the North Report and the Wegman Report.
Many press reports said that the North report supported the “hockey stick”, however
looking beyond the summary reveals a different perspective:
(The below is cut and pasted from the report with our comments in [brackets])
Surface Temperature Reconstructions for the Last 2,000 Years
Committee on Surface Temperature Reconstructions for the Last 2,000 Years,
National Research Council
From Page 111 (sheet 126) bold added:
OVERALL FINDINGS AND CONCLUSIONS
Based on its deliberations and the materials presented in Chapters 1_11 and elsewhere,
the committee draws the following overall conclusions regarding large_scale surface
reconstructions for the last 2,000 years:
* The instrumentally measured warming of about 0.6?C during the 20th century is
also reflected in borehole temperature measurements, the retreat of glaciers, and
other observational evidence, and can be simulated with climate models.
.......[This verifies that there was about a 0.6?C temperature increase during the
20th century (see below)]
* Large_scale surface temperature reconstructions yield a generally consistent picture
of temperature trends during the preceding millennium, including relatively warm
conditions centered around A.D. 1000 (identified by some as the “Medieval Warm Period”)
and a relatively cold period (or “Little Ice Age”) centered around 1700. The existence
and extent of a Little Ice Age from roughly 1500 to 1850 is supported by a wide
variety of evidence including ice cores, tree rings, borehole temperatures, glacier
length records, and historical documents.
......[This re_affirms the existence of a “little ice age”]
Evidence for regional warmth during medieval times can be found in a diverse but
more limited set of records including ice cores, tree rings, marine sediments, and
historical sources from Europe and Asia, but the exact timing and duration of warm
periods may have varied from region to region, and the magnitude and geographic extent
of the warmth are uncertain.
....[This re_affirms the existence of a “medieval warm period”]
....[Remember the famous “hockey stick” chart? It DOES NOT show either the “little
ice age” or “medieval warm period”. This omission disproves the “hockey stick” chart
and the data/methods used to create it. Much of the climate field uses similar data
* It can be said with a high level of confidence that global mean surface temperature
was higher during the last few decades of the 20th century than during any comparable
period during the preceding four centuries. This statement is justified by the consistency
of the evidence from a wide variety of geographically diverse proxies.
....[This is the headline for many newspapers. Most forgot to mention that the
“preceding four centuries” started in the middle of the “little ice age (above).
In other words, we are warming up after the little ice age.]
* Less confidence can be placed in large_scale surface temperature reconstructions
for the period from A.D. 900 to 1600. Presently available proxy evidence indicates
that temperatures at many, but not all, individual locations were higher during the
past 25 years than during any period of comparable length since A.D. 900. The uncertainties
associated with reconstructing hemispheric mean or global mean temperatures from
these data increase substantially backward in time through this period and are not
yet fully quantified.
* Very little confidence can be assigned to statements concerning the hemispheric
mean or global mean surface temperature prior to about A.D. 900 because of sparse
data coverage and because the uncertainties associated with proxy data and the methods
used to analyze and combine them are larger than during more recent time periods.
.....[ This says that we really don’t know enough about climate before A.D 900. This
suggests that we are incapable of judging today’s climate in a proper historical
context, considering that there has been 12,000 years of ups and downs since the
last ice age. We only know about 10% of this time span to a sufficient degree.]
__________________________ From page 21 (sheet36) Bold Added ____________________________________
Based on the analyses presented in the original papers by Mann et al. and this newer
supporting evidence, the committee finds it plausible that the Northern Hemisphere
was warmer during the last few decades of the 20th century than during any comparable
period over the preceding millennium.
.....[Note that this claim is only “plausible”, not likely or probable or “supported
by a wide variety of evidence” (see above)]
The substantial uncertainties currently present in the quantitative assessment of
large_scale surface temperature changes prior to about A.D. 1600 lower our confidence
in this conclusion compared to the high level of confidence we place in the Little
Ice Age cooling and 20th century warming. Even less confidence can be placed in the
original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest
decade, and 1998 the warmest year, in at least a millennium” because the uncertainties
inherent in temperature reconstructions for individual years and decades are larger
than those for longer time periods, and because not all of the available proxies
record temperature information on such short timescales.
....[Here is the often heard statement that we are the warmest in 1000 years. It
is given “less confidence” than “plausible” (see above). Effectively, it is shown
to be baseless.]
______________________Some Thoughts About the Above Report ______________________________
We believe that the two most gripping claims about global warming have been shown
to be wrong. The other major claim, that we are the warmest in 400 years is essentially
a statement that we are warming after the “little ice age.” Is that bad?
National Academy of Sciences, National Research Council report (North Report)
National Academy of Sciences, National Research Council report (Wegman Report)
Wegman’s bio from George Mason U: http://www.galaxy.gmu.edu/stats/faculty/wegman.html
Here is a short sample:
Dr. Wegman served in national office in the Institute of Mathematical Statistics,
the American Statistical Association and the American Association for the Advancement
of Science. He served as President of the International Association for Statistical
Computing. He has published more than 160 papers and eight books. His professional
stature has been recognized by his election as Fellow of the American Statistical
Association, the American Association for the Advancement of Science, the Washington
Academy of Science and the Institute of Mathematical Statistics.
Wegman Report, item 7, page 49 (MBH is the hockey stick paper): Our committee believes
that the assessments that the decade of the 1990s was the hottest decade in a millennium
and that 1998 was the hottest year in a millennium cannot be supported by the MBH98/99
Wegman Report, item 7, page 49: The cycle of Medieval Warm Period and Little Ice
Age that was widely recognized in 1990 has disappeared from the MBH98/99 analyses,
thus making possible the hottest decade/hottest year claim. However, the methodology
of MBH98/99 suppresses this low frequency information. The paucity of data in the
more remote past makes the hottest-in-a-millennium claims essentially unverifiable.
Wegman Report, item 6, page 49:Generally speaking, the paleoclimatology community
has not recognized the validity of the MM05 papers and has tended dismiss their results
as being developed by biased amateurs.
Wegman Report, page 52: Conclusion 4. While the paleoclimate reconstruction has
gathered much publicity because it reinforces a policy agenda, it does not provide
insight and understanding of the physical mechanisms of climate change except to
the extent that tree ring, ice cores and such give physical evidence such as the
prevalence of green-house gases. What is needed is deeper understanding of the physical
mechanisms of climate change.
Wegman Report, page 49: 1. In general we found the writing of MBH98 somewhat obscure
and incomplete. The fact that MBH98 issued a further clarification in the form of
a corrigendum published in Nature (Mann et al. 2004) suggests that these authors
made errors and incomplete disclosures in the original version of the paper. This
also suggests that the refereeing process was not as thorough as it could have been.
Wegman Report, page 49:2. In general, we find the criticisms by MM03, MM05a and
MM05b to be valid and their arguments to be compelling. We were able to reproduce
their results and
offer both theoretical explanations (Appendix A) and simulations to verify that their
observations were correct. . .
Wegman Report, page 49, item 3: . . Because the temperature profile in the 1902-1995
is not similar, because of increasing trend, to the millennium temperature profile,
it is not fully appropriate for the calibration and, in fact, leads to the misuse
of the principal components analysis. However, the narrative in MBH98 on the surface
sounds entirely reasonable on this calibration point, and could easily be missed
by someone who is not extensively trained in statistical methodology. Dr. Mann has
close ties to both Yale University and Pennsylvania State University. We note in
passing that both Yale University and Pennsylvania State University have Departments
of Statistics with excellent reputations9. Even though their work has a very significant
statistical component, based on their literature citations, there is no evidence
that Dr. Mann or any of the other authors in paleoclimatology studies have significant
interactions with mainstream statisticians.
Wegman Report, page 49: Although we have not addressed the Bristlecone Pines issue
extensively in this report except as one element of the proxy data, there is one
point worth mentioning. Graybill and Idso (1993) specifically sought to show that
Bristlecone Pines were CO2 fertilized. Bondi et al. (1999) suggest [Bristlecones]
“are not a reliable temperature proxy for the last 150 years. . .
Wegman Report, page 52: Conclusion 4. While the paleoclimate reconstruction has gathered
much publicity because it reinforces a policy agenda, it does not provide insight
and understanding of the physical mechanisms of climate change except to the extent
that tree ring, ice cores and such give physical evidence such as the prevalence
of green-house gases. What is needed is deeper understanding of the physical mechanisms
of climate change.
Wegman: page 4: In our further exploration of the social network of authorships in
temperature reconstruction, we found that at least 43 authors have direct ties to
Dr. Mann by virtue of coauthored papers with him. Our findings from this analysis
suggest that authors in the area of paleoclimate studies are closely connected and
thus “independent studies” may not be as independent as they might appear on the
(Bold added; from: 07142006_Wegman_Report.pdf )
Corrected Hockey Stick
As mentioned above, McIntyre & McKitrick(2003) found errors in the hockey stick.
They also published a corrected version shown above.