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20 Questions Statisticians Should Ask!

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Paleoclimate reconstruction uses proxies to estimate temperature ... Lonnie Thompson's Ice Cores and Nobel Laureate Al Gore. Paleoclimate Reconstruction ... – PowerPoint PPT presentation

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Title: 20 Questions Statisticians Should Ask!


1
20 Questions Statisticians Should Ask!
  • Edward J. Wegman
  • George Mason University
  • ASA A Statistical Consensus on Global Warming
  • October 27, 2007

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Looking Backwards Looking Forwards
  • Paleoclimate reconstruction uses proxies to
    estimate temperature profiles in the past.
  • Climate models use physical/statistical models
    usually based on PDEs to understand/predict/projec
    t temperature and other climate variables in the
    future.
  • Both have a fundamental statistical/stochastic
    character.

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Paleoclimate Reconstruction
After Bradley (1999)
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Paleoclimate Reconstruction
After Bradley and Eddy (1991)
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Paleoclimate Reconstruction
Confounding Factors?
After Bradley and Eddy (1991)
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Paleoclimate Reconstruction
  • climate field reconstruction (CFR)
  • principal component based (almost)
  • empirical orthogonal function analysis
  • data matrix columns are time series of proxy data
  • weighted to largest variance
  • climate plus scale (CPS)
  • simple averages of proxies

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Paleoclimate Reconstruction
  • tree rings
  • tree ring size and density variations
  • best signal when trees are stressed
  • latitude and altitude
  • Precipitation and CO2 fertilization
  • ice cores
  • ice layer thickness
  • oxygen and hydrogen isotope balance
  • coral
  • annual growth
  • symbiosis with algae

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Paleoclimate Reconstruction
TREE RINGS
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Paleoclimate Reconstruction
Bristlecone Pines
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Paleoclimate Reconstruction
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Statistical Questions
  • How were the 70 trees in NOAMER 1400 selected?
  • How representative are these trees of the
    population of trees that grew from 1400-2000? In
    terms of geography, altitude, and type.
  • If these trees seemed interesting to various
    individuals who took the core samples, should one
    believe those trees can/should be treated as a
    random sample? Are there biases in the
    selection of these trees?
  • Presumably many trees could not be sampled
    because they had died or been harvested. What is
    the effect of this censoring on the data (and
    the analysis)?
  • What is the correlation between temperature and
    tree ring growth?

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Hockey Sticks
Top Panel is original EOF (CFD) method applied to
North American Tree Proxy, PC1. Bottom Panel is
the result of the centered PCA.
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Paleoclimate Reconstruction
Ice Cores
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Paleoclimate Reconstruction
Lonnie Thompsons Ice Cores and Nobel Laureate Al
Gore
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Paleoclimate Reconstruction
  • 5. Similar questions exist about ice cores
    and how representative such data might be. What
    are the effects of gas diffusion in the ice core
    layers?
  • 6. In the ice core (Vostok) data that Al Gore
    illustrates in the Inconvenient Truth, the
    temperature time series leads, not lags, the CO2
    time series by 800 to 1000 years. What is the
    causal mechanism? It would seem that temperature
    increases cause CO2 release, not vice versa. The
    common answer is that there is an (unspecified)
    feedback mechanism.

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Paleoclimate Reconstruction
Corals
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Two Mode Proxy-Paper Network
Most Common Proxies
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Paleoclimate Reconstruction
  1. Why are the same proxies used in so many papers?
    Most recently, Osborn and Briffa (2006), DArrigo
    et al. (2006), Juckes et al. (2007). Mann et al.
    (1998, 1999) was ground breaking in using
    hundreds of proxies. Most more recent papers
    focus on the top 15 or so in our two-mode
    network. Are they chosen because they show the
    hockey stick and those omitted dont?

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Statistical Questions
  1. What calibration studies have been performed?
    Rescaling steps seem to suggest that the
    correlation must be near 100. Is that the case?
    How are the confounding variables removed?
  2. The temperature proxy search is a regression
    problem. Why should one choose to use principal
    components (not appropriate for finding a
    nonstationary mean)?
  3. What weights are used to combine different proxy
    types? Why?
  4. If the data are not a random sample, then what
    confidence can be given to any modeling and to
    any error bars? Why pointwise confidence
    intervals in place of confidence bands? Is new
    theory needed?

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Statistical Questions
  1. Most models are deterministic, estimating the
    expected temperature or other component. To what
    extent are these models chaotic systems? How
    thoroughly has this been investigated?
  2. For coupled ocean-atmosphere-land models, how
    much more likely is this to induce chaotic
    behavior?
  3. Models depend on initial conditions often derived
    from remote sensing sources. How well calibrated
    to ground truth are these?
  4. CO2 modeling shows a rapid increase in the near
    term. What do the models show in the longer term?
  5. Given the apparent high correlation between CO2
    and temperature in the model outputs, how direct
    is the link in the model itself?

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Statistical Questions
  1. What data should be collected that would be most
    cost-effective in increasing our understanding of
    the climatic models and the underlying physics
    (and statistics)?
  2. Are all data valuable? How does one avoid the
    desire to collect data at sites that appear
    interesting beforehand?

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Statistical Questions
Melbournes Historic Weather Station 1855 to
2007
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Statistical Questions
  1. To what extent have the micro-climates changed
    the instrumented temperature record? How have
    this effect been compensated for, especially in
    the absence of accurate records of original
    micro-climate? What is the impact of changing and
    improving technology?
  2. How is the instrumented temperature record
    associated with the increase or decrease in the
    number of weather stations?

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Statistical Questions
29
Statistical Questions
  • Bonus Question 21. Why to climate scientists show
    two side-by-side pictures and say look how well
    they compare? Subtract them and see how well they
    dont compare.

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Contact Information
Where to send climate police Edward J.
Wegman Department of Computational and Data
Sciences George Mason University Fairfax, VA
22030 Email ewegman_at_gmail.com
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