Sunday, April 1, 2012


date: Tue, 07 Feb 2006 11:46:15 -0500
from: "Michael E. Mann" <>
subject: Re: Questions
to: Sara Goudarzi <>

HI Sara,
Thanks, I feel I have enough info to answer the questions you pose now. Please let me know
if you could use any further feedback from me on this,
best regards,
Sara Goudarzi wrote:

Hi Mike,

Below, please find my list of questions. Again, I very much appreciate the time you are
taking out to answer these.



1. What do you think about the use of the so-called "proxy" climate records (not direct
temp measurements but the change of environmental conditions), which is what the
researchers used?

there is a rich history of the use of climate "proxies" (tree-ring, ice cores, corals, lake
sediments, etc.) in the field of paleoclimatology. The field has come a long way, growing
increasingly more rigirous in recent decades. There is enough information now to draw
reasonably robust conclusions, not just in terms of the proxy data that are available, but
also our understanding of all of the caveats and uncertainties, given the inexact nature of
the data. In this case, the authors by-passed the thorny issue of precisely how to
calibrate the proxy data, by taking a more common sense approch. They have simply examined
the data to determine how widespread the patterns of evidence for "cold" or "warm" behavior
were, over different periods spanning the past 1200 years.

2. The researchers used data sources such as tree ring records, ice cores, historical
records and chemical composition of cells. What are your th! oughts on these sources as
indicators of climate data?

these are all useful proxy records, as they record some attribute about the environment
(e.g. favorability of growing season conditions, chemical isotopes that correlate with
temperatures, etc.). However, the interpretation of the climate signal provided by any
particular proxy can be challenging to ascertain in many cases. Recognizing this, the
authors have sought to insure that the data they used were indeed proxy indicators of
"temperature" by screening the data set to include only those data which correlate with
nearby instrumental temperature records over the modern interval.

3. The researchers found that the most widespread warmth was found during the 20th century
and similar expanses of warm conditions in the mid and late 20th century. How does this
compare with what was previously thought? i.e did previous research know this?

This is an independent approach from that used in other previous "proxy" studies of
long-term temperature trends, and so the conclusions of the approach the authors take are
complementary to those arrived at in past studies. Yet the primary conclusion--that late
20th century/early 21st century warmth is anomalous in the context of at least the past
1000 years--is consistent with that drawn from other past studies.

4. Why does this research matter and what does it tell us?

The authors making a compelling case the recent anomalous warmth is not coincidental but,
instead, likely related to recent anthropogenic impacts on climate and, in particular,
human-caused greenhouse gas concentration increases.

5. I know you don't have the paper, but from what you know are there any concerns that you
have with this type of data sources and statistical analysis?

As mentioned above, the authors have sought to insure that the data they used were indeed
proxy indicators of "temperature" by screening the data set to include only those data
which correlate with nearby instrumental temperature records over the modern interval.
They have also bypassed the thorny issue of "calibration". The analysis is straightforward,
and the conclusions likely quite robust.

6. What are your thoughts on the overall research and results?

This latest paper might be the "nail in the coffin" for the small minority of very vocal
climate change denialists who continue to try to challenge the conclusion that the recent
warming of the Earth's surface is anomalous. This paper adds to the weight of
already-existing evidence that recent warmth is anomalous in a very long-term context.
Model simulations over the time time interval indicate that only the anthropogenic
iincreases in greenhouse gas concentrations over the past 1-2 centuries can explain this.
But this paleoclimate information comprises only one of many independent lines of evidence
indicating a primary role of human impacts on modern-day global warming. Indeed, it is
remarkable that there is still a public debate, given the tremendous weight of mounting
scientific evidence that human-caused global warming is already detectable, and will
continue to accelerate in the absence of societal intervention.


Sara Goudarzi

[3]Yahoo! Mail - Helps protect you from nasty viruses.

Michael E. Mann
Associate Professor
Director, Earth System Science Center (ESSC)

Department of Meteorology Phone: (814) 863-4075
503 Walker Building FAX: (814) 865-3663
The Pennsylvania State University email: [4]
University Park, PA 16802-5013


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