Steve McIntyre - Do We Know that the 1990s Were the Warmest Decade of the Millennium?

1. Do We Know that the
1990s were the Warmest
Decade of the Millennium?
Stephen McIntyre
climateaudit.org
Toronto Ontario
2009 International Conference on
Climate Change
New York
March 9, 2009
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2. Questions
1. How do they “know” that 1998 was the
warmest year of the millennium?
They don’t. Minor variations
in data versions (e.g.
bristlecones) yield opposite
results.
2. Does it “matter”?
For “big” policy, probably not.
But it’s an interesting question
and statistics should be done
“right”.
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3. IPCC 2001: The Rise of the Stick
The “Hockey Stick” graph, attributed to Mann et al (Nature 1998, GRL
1999 (MBH), occurred six times in IPCC TAR. Inset: John Houghton at
IPCC Press Conference, 2001
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4. The Soundbites: “The Warmest
Decade and Year”
The 20th century was the warmest in the Northern Hemisphere
in the past 1000 years. The 1990s was the warmest decade on
record and 1998 was the warmest year - in Canada and
internationally. - David Anderson, April 5, 2002
The 20th century was the warmest in the Northern Hemisphere
for the past 1000 years and the 1990s the warmest decade on
record... The science of climate change has been subjected to
international scrutiny, open to all qualified experts, peer review,
atmospheric modeling and process studies. – Liberal Party of
Canada Caucus, Aug. 22, 2002
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5. “As Dr Thompson’s Thermometer
Shows,…”
…the vaunted Medieval Warm Period (the third little red blip from the left below)
was tiny in comparison to the enormous increases in temperature in the last
half-century - the red peaks at the far right of the graph. These global-warming
skeptics - a group diminishing almost as rapidly as the mountain glaciers -
launched a fierce attack against another measurement of the 1000 year
correlation between CO2 and temperature known as the “hockey stick”, a
graphic image representing the research of climate scientist Michael Mann and
his colleagues.”
Gore actually shows Mann’s reconstruction spliced with the Jones
instrumental record.
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6. IPCC 2007: Spaghetti Graphs
It is likely that this 50-year period was the warmest
Northern Hemisphere period in the last 1.3 kyr,
Excerpt from IPCC 2007 Box 6.4 Figure 1..
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7. “Multivariate Calibration”
McIntyre and McKitrick, 2009: “Paleoclimate
reconstructions are an application of multivariate
calibration, which provides a theoretical basis for
confidence interval calculation (e.g., Osborne 1991;
Brown and Sundberg, 1987). Inconsistency among
proxies sharply inflates confidence intervals. Applying the
inconsistency test of [Brown and Sundberg] to Mann et
al. A.D. 1000 proxy data shows that finite confidence
intervals cannot be defined before 1800.”
MBH2009: The method of uncertainty estimation (use of
calibration/validation residuals) is conventional
[Luterbacher et al 2004; Wahl and Ammann 2007]
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8. “Small and uninteresting
perturbations” of data/technique
de Leeuw (1988): We usually do not want a small
and uninteresting perturbation of our data to have a
large effect on the results of our technique. Classical
statistics has always studied stability by using standard
errors or confidence intervals. Gifi thinks this is much
too narrow and other forms of stability are important as
well…
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9. MM2005 on “slight variations of
methods and data”
Redrawn from MM2005b
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10. MBH98 AD1400 Proxies
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11. There is no dispute over
properly specified calculations
Top Left: MBH, 2003; top right; Bürger et al 2006; bottom –drawn
from calculations using Wahl and Ammann 2007 algoithm. Middle-
varies PC method (their Scenario 5); right - varies bristlecones (Their
11Scenario 6).

12. NAS 2006
For periods prior to the 16th century, the
Mann et al. (1999) reconstruction that uses
this particular principal component analysis
technique is strongly dependent on data
from the Great Basin region in the western
United States [bristlecones]….
some reconstructions are not robust with
respect to the removal of proxy records
from individual regions (see, e.g., Wahl and
Ammann in press)….
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13. IPCC 2007
The McIntyre and McKitrick 2005a,b criticism
[relating to the extraction of the dominant
modes of variability present in a network of
western North American tree ring chrono-
logies, using Principal Components Analysis]
may have some theoretical foundation, but
Wahl and Amman (2006) also show that the
impact on the amplitude of the final
reconstruction is very small (~0.05°C).
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14. Wahl and Ammann (“in press
2005”; “in press 2006”; Sep. 2007)
“when the full information in the proxy data is
represented by the PC series [i.e. enough to get the
bristlecones in], the impact of PC calculation methods
on climate reconstruction in the MBH method is
extremely small… a slight modification to the original
Mann et al. reconstruction is justifiable for the first half
of the 15th century (∼+0.05–0.10◦), which leaves
entirely unaltered the primary conclusion of Mann et
al.”…
[Bristlecones add] “necessary verification skill” …
“indicating that the records carry important climate
information at the level of eigenvector patterns in global
surface temperatures. These results are valid
notwithstanding issues concerning these proxies’
empirical relationship to local/regional surface
temperatures after 1850”
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15. Wegman 2006
Wahl and Ammann [argue] that if one adds
enough principal components back into the
proxy, one obtains the hockey stick shape
again. This is precisely the point of
contention…
A cardinal rule of statistical inference is that
the method of analysis must be decided
before looking at the data. The rules and
strategy of analysis cannot be changed in
order to obtain the desired result. Such a
strategy carries no statistical integrity and
cannot be used as a basis for drawing
sound inferential conclusions.
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16. A “Dozen Independent Studies”
Mann (Senate Testimony, 2003): More than a dozen
independent research groups have now reconstructed the
average temperature of the northern hemisphere in past
centuries..
Wigley (AP Interview, 2003): about a dozen independent
studies suggest the 20th century was warmer than normal,
Wigley points out.
Mann (Letter to House Committe, 2005): Recent work since
the TAR has provided further support for this conclusion [
the Stick], which is now common to more than a dozen
independent studies published in the peer-reviewed
scientific literature.
Wikipedia 2009: More than a dozen independent research
groups have now reconstructed the average temperature
of the northern hemisphere in past centuries.
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17. “Not Entirely Independent”
IPCC 2007: As with the original TAR series, these new
records are not entirely independent reconstructions
inasmuch as there are some predictors (most often tree
ring data and particularly in the early centuries) that are
common between them, but in general, they represent
some expansion in the length and geographical
coverage of the previously available data (Figures 6.10
and 6.11
NAS 2006: Because the data are so limited, different
large-scale reconstructions are sometimes based on the
same datasets, and thus cannot be considered as
completely independent.
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18. Key proxies are repeated in so-called
“independent” spaghetti graph studies
Above – Adapted from Wegman 2006 Figure 5.8. Bristlecones/
foxtails are used in all but three spaghetti graph studies. Polar Urals
and Tornetrask versions re used in every study.
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19. Ecologists: warm California MWP
Miller et al 2006 (Quat Res): “Using contemporary distributions of
the species, we modeled paleoclimate during [the MWP] to be
significantly warmer (+3.2 deg C annual minimum temperature)
and slightly drier (-24 mm annual precipitation) than present.
Left- Bristlecone treeline (Lamarche 1973) declined since MWP; right –
Subfossil medieval trees above present treeline at Whitewing Mt, Sierra
Nevadas, California.
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20. “Heavy” Equipment
IPCC 2007: the possibility of investigating
[these issues] further is restricted by the
lack of recent tree ring data at most of the
sites from which tree ring data discussed in
this chapter were acquired
Michael Mann: paleoclimatologists are
attempting to update many important proxy
records to the present, this is a costly, and
labor-intensive activity, often requiring
expensive field campaigns that involve
traveling with heavy equipment to difficult-
to-reach locations (such as high-elevation or
remote polar sites). For historical reasons,
many of the important records were
obtained in the 1970s and 1980s and have
yet to be updated.
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21. Ababneh 2006 did not replicate
Graybill’s bristlecone chronology
Left – red – MBH PC1 (used in IPCC 2007 Box 6.4) ; green – Graybill
Sheep Mt chronology. Right - Ababneh (2006, 2007) chronology.. All
series scaled to 1400-1980. 950-1100 and 1856-1980 highlighted.
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22. Almagre CO Bristlecones are not
setting records
Decline in recent portion of the chronology. The most noticeable
feature is the low growth in the1840-50s – associated with
drought in other Colorado tree ring chronologies.
Left- MBH PC1 (bristleocnes); right – updated Almagere
chronology. In dimensionless chronology units, basis 1.
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23. Controversial “Starbucks Hypothesis”
Proven!
Left – 7 am at Starbucks, Colorado Springs; right – bristlecones at 3600 m;
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24. Almagre program identified exact trees during
update and measurements online within 3 months
Left – Pete Holzmann sampling Tree 31 in 2007; right- Donald Graybill
sampling same tree in 1987.
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25. Strip Bark: simple statistical models
don’t apply
Graybill and Idso 1993: Another tree selection factor that is crucial to our
findings involves tree form... [Strip bark trees] were the primary focus of
investigation wherever possible, (Brunstein USGS
2006http://www.climateaudit.org/?p=2239
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26. Key proxies are used over and over.
Above – From Wegman 2006 Figure 5.8 showing proxy overlap;
IPCC 2007 Box 6.4 Fig 1.
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27. Polar Urals: Briffa (Jones) 1995
Above – Polar Urals version of Briffa et al 1995, used in Jones et al 1998
reconstruction. All series scaled to scale of Briffa et al 1995. 950-1100 and 1856-1980
highlighted.
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28. Evidence for warm MWP in Siberia
Left - Polar Urals treeline declined since Medieval Warm Period (from
Shiyatov 1995); right – subfossil medieval trees in foreground above
modern treeline in background (Esper);
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29. Polar Urals Update
Above – Polar Urals version incorporated into Esper et al 2002. All
series scaled to scale of Briffa et al 1995. 950-1100 and 1856-1980
highlighted.
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30. Yamal Substitution (Briffa 2000)
Above - Yamal chronology from Briffa 2000, used in all but one
subsequent study. All series scaled to scale of Briffa et al 1995. 950-
1100 and 1856-1980 highlighted.
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31. Tornetrask: Briffa 2000 vs Grudd
2006
Left – Version used in IPCC 2007. Right - Grudd 2006. All series scaled to scale
of Briffa et al 1995. 950-1100 and 1856-1980 highlighted.
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32. Are ice cores any help?
wide variety of ice core

patterns since MWP.
δO18 at Mt Logan,

Yukon went down in
20th (attributed to
regional change);
Elevated δO18 at Law

Dome, Antarctica ignored
by NAS panel
Ice core δO18 from N to S.
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33. Different Spaghetti Recipes
NRC panel used 4 reconstructions as comfort for comparing
modern-medieval levels, but did not verify that cited
reconstructions met proxy quality standards. Medieval-modern
relationship reverses with trivial and justifiable variations in proxy
selection.
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34. Glacier Retreat: Alberta
Retreat of Saskatchewan Glacier (in
Alberta) in 1999 exposed in situ stumps
dated ~2800-2900 BP (14C) presumably
not exposed in MWP
In… August 1999, a severe rainstorm resulted in stream
avulsion along the NE flank of the Saskatchewan Glacier snout
… When first examined in early September, erosion through a
3- to 5- m sequence of glacial outwash and overlying till had
exposed 17 sheared stumps rooted within a well-preserved
paleosol …. By September 2000, the meltwater channel had
shifter southward and had eroded through 5 m of fluted moraine
deposits exposing 2 additional rooted stumps and flushing an
additional 40 detrital boles onto the outwash surface. The
stumps were rooted in a deeply weathered pedogenic surface
and prior to their exposure were buried by 3-5 m of sediment. …
With one exception, these dates collectively reflect the
consequences of a single Neoglacial advance of the
Saskatchewan Glacier into an established valley bottom forest.
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35. Quelccaya Glacier, Peru
Distichia muscoides, a component of
Andean peat deposits, exposed in recent
Quelccaya glacier retreat. Present limit is
400-500 m lower than the discovery.
Peat samples have a wide variety of
14C dates - many about 4500 BP.
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36. Green Alps
Left- modern view of a pass in the Alps (with glacier lines of 1922
and 1856); right - Schlüchter and Jörin 2004 reconstruction of view
Roman times of 2000 years ago
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37. Does it matter?
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38. Why did IPCC feature the “least
important” figure?
It is one of those odd ironies that the figure that everyone
keeps talking about is actually the least important from the
point of view of understanding climate responses to forcing.
Gavin Schmidt, 2005
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39. Is it the “Least Important” Figure?
Left: IPCC 2001 Synthesis for Policy makers Figure SPM-10b with MBH
reconstruction; Right: IPCC 1990 version of Lamb (about 1 deg range)
together with IPCC 2007 SPM range of scenarios: yellow shows
“constant 2000 GHG”.
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40. “Worse than We Thought”
There is (yet another) odd inversion about: the idea that if
we were to switch from, say, MBH (less variance) to Moberg
(more) that would somehow imply a reduction in expected
future warming. That is completely wrong. If the past
temperatures varied more, it implies a *higher* sensitivity to
forcing, and therefore a *higher* future William Connolley,
2005
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41. Visit www.climateaudit.org for
ongoing discussion.
Presentation will be posted at
www.climateaudit.org/pdf/newyork09
with bibliography
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