Title: 20 Questions Statisticians Should Ask!
120 Questions Statisticians Should Ask!
- Edward J. Wegman
- George Mason University
- ASA A Statistical Consensus on Global Warming
- October 27, 2007
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5Looking 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.
6Paleoclimate Reconstruction
After Bradley (1999)
7Paleoclimate Reconstruction
After Bradley and Eddy (1991)
8Paleoclimate Reconstruction
Confounding Factors?
After Bradley and Eddy (1991)
9Paleoclimate 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
10Paleoclimate 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
11Paleoclimate Reconstruction
TREE RINGS
12Paleoclimate Reconstruction
Bristlecone Pines
13Paleoclimate Reconstruction
14Statistical 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?
15Hockey Sticks
Top Panel is original EOF (CFD) method applied to
North American Tree Proxy, PC1. Bottom Panel is
the result of the centered PCA.
16Paleoclimate Reconstruction
Ice Cores
17Paleoclimate Reconstruction
Lonnie Thompsons Ice Cores and Nobel Laureate Al
Gore
18Paleoclimate 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.
19Paleoclimate Reconstruction
Corals
20Two Mode Proxy-Paper Network
Most Common Proxies
21Paleoclimate Reconstruction
- 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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23Statistical Questions
- 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? - The temperature proxy search is a regression
problem. Why should one choose to use principal
components (not appropriate for finding a
nonstationary mean)? - What weights are used to combine different proxy
types? Why? - 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?
24Statistical Questions
- 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? - For coupled ocean-atmosphere-land models, how
much more likely is this to induce chaotic
behavior? - Models depend on initial conditions often derived
from remote sensing sources. How well calibrated
to ground truth are these? - CO2 modeling shows a rapid increase in the near
term. What do the models show in the longer term?
- Given the apparent high correlation between CO2
and temperature in the model outputs, how direct
is the link in the model itself?
25Statistical Questions
- 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)? - Are all data valuable? How does one avoid the
desire to collect data at sites that appear
interesting beforehand?
26Statistical Questions
Melbournes Historic Weather Station 1855 to
2007
27Statistical Questions
- 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? - How is the instrumented temperature record
associated with the increase or decrease in the
number of weather stations?
28Statistical Questions
29Statistical 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.
30Contact 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