1

Do We Know that the 1990s were the Warmest

Decade of the Millennium? Stephen McIntyreclimateaudit.orgToronto Ontario

2009 International Conference on Climate Change New YorkMarch 9, 2009

2

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”.

Questions

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

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

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.

6

IPCC 2007: Spaghetti Graphs

Excerpt from IPCC 2007 Box 6.4 Figure 1..

It is likely that this 50-year period was the warmest Northern Hemisphere period in the last 1.3 kyr,

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]

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…

9

MM2005 on “slight variations of methods and data”

Redrawn from MM2005b

10

MBH98 AD1400 Proxies

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 Scenario 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)….

13

IPCC 2007The 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).

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”

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.

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.

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.

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.

19

Ecologists: warm California MWP

Left- Bristlecone treeline (Lamarche 1973) declined since MWP; right – Subfossil medieval trees above present treeline at Whitewing Mt, Sierra Nevadas, California.

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.

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.

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.

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.

23

Controversial “Starbucks Hypothesis” Proven!

Left – 7 am at Starbucks, Colorado Springs; right – bristlecones at 3600 m;

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.

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

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.

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.

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);

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.

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.

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.

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.

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.

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 MWPIn… 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.

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.

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

37

Does it matter?

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

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”.

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

41

Visit www.climateaudit.org for ongoing discussion.

Presentation will be posted at www.climateaudit.org/pdf/newyork09 with bibliography