Tuesday, April 3, 2012


date: Thu Jul 3 16:52:36 2003
from: Tim Osborn <t.osbornatXYZxyz.ac.uk>
subject: Fwd: 03-19 Mann - climate change press release - first draft
to: k.briffa@uea

Keith - you might want to take a close look at this press release, in case (i) it is
inappropriate, or (ii) you want to be contacted by the media because Phil & Mike are in

Date: Thu, 03 Jul 2003 11:04:26 -0400
From: Harvey Leifert <HLeifertatXYZxyz.org>
Organization: AGU
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.3.1) Gecko/20030425
X-Accept-Language: en-us, en
To: "Michael E. Mann" <mannatXYZxyzginia.edu>
CC: f028 <P.JonesatXYZxyz.ac.uk>, tim Osborn <t.osbornatXYZxyz.ac.uk>
Subject: 03-19 Mann - climate change press release - first draft
Hi Mike,
Thanks for the background information, some of which I have incorporated into the draft
below. Please send me your corrections and/or suggestions asap. In particular, is the
title ok or too strong regarding human activity? I also need contact information (phone
and email) for whichever authors you think should be able to handle media queries
resulting from this release. In the case of you and Phil, I need Sapporo numbers, as
well as your permanent ones. (Not all authors are AGU members, it seems, and therefore
not in our database.) If the changes are not major, I'll just make them and issue the
release; if you want to see a second draft, let me know. Thanks!
[Title] Leading Climate Scientists Reaffirm View That Late 20th Century Warming Was
Unusual and Resulted From Human Activity
WASHINGTON - A group of leading climate scientists has reaffirmed the "robust consensus
view" emerging from the peer reviewed literature that the warmth experienced on at least
a hemispheric scale in the late 20th century was an anomaly in the previous millennium
and that human activity likely played an important role in causing it. In do doing, they
refuted recent claims that the warmth of recent decades was not unprecedented in the
context of the past thousand years.
Writing in the 8 July issue of the American Geophysical Union publication Eos, Michael
Mann of the University of Virginia and 12 colleagues in the United States and United
Kingdom endorse the position on climate change and greenhouse gases taken by AGU in
1998. Specifically, they say that "there is a compelling basis for concern over future
climate changes, including increases in global-mean surface temperatures, due to
increased concentrations of greenhouse gases, primarily from fossil-fuel burning."
The Eos article is a response to two recent and nearly identical papers by Drs. Willie
Soon and Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics, published
in Climate Research and Energy & Environment (the latter paper with additional
co-authors). They challenge the generally accepted view that natural factors cannot
fully explain recent warming and must have been supplemented by significant human
activity, and their papers have received attention in the media and in the U.S. Senate.
Requests from reporters to top scientists in the field, seeking comment on the Soon and
Baliunas position, lead to memoranda that were later expanded into the current Eos
article, which was itself peer reviewed.
Mann and his colleagues rely on instrumental data for the past 150 years and "proxy"
indicators, such as tree rings, ice cores, corals, and lake sediments to reconstruct the
climate of earlier times. Most of the available data pertain to the northern hemisphere
and show, according to the authors, that the warmth of the northern hemisphere over the
past few decades is likely unprecedented in the last 1,000 years and quite possibly in
the preceding 1,000 years as well.
Climate model simulations cannot explain the anomalous late 20th century warmth without
taking into account the contributions of human activities, the authors say. They make
three major points regarding Soon and Baliunas's recent assertions challenging these
First, in using proxy records to draw inferences about past climate, it is essential to
assess their actual sensitivity to temperature variability. In particular, the authors
say, Soon and Baliunas misuse hydrological data in their effort to determine
Second, it is essential to distinguish between regional temperature anomalies and
hemispheric mean temperature, which must represent an average of estimates over a
sufficiently large number of distinct regions. For example, Mann and his co- authors
say, the concepts of a "Little Ice Age" and "Medieval Warm Period" arose from the
Eurocentric origins of historic climatology. The specific periods of coldness and warmth
differed from region to region and as compared with data for the northern hemisphere as
a whole.
Third, according to Mann and his colleagues, it is essential to define carefully the
modern base period with which past climate is to be compared and to identify and
quantify uncertainties. For example, they say, the most recent report of the
Intergovernmental Panel on Climate Change (IPCC) carefully compares data for recent
decades with reconstructions of past temperatures, taking into account the uncertainties
in those reconstructions. IPCC concluded that late 20th century warmth in the northern
hemisphere likely exceeded that of any time in the past millennium. The method used by
Soon and Baliunas, they say, considers mean conditions for the entire 20th century as
the base period and determines past temperatures from proxy evidence not capable of
resolving trends on a decadal basis. It is therefore, they say, of limited value in
determining whether recent warming in anomalous in a long term and large scale context.
The Eos article started as a memorandum that Michael Oppenheimer and Mann drafted to
help inform colleagues who were being contacted by members of the media regarding the
Soon and Baliunas papers and wanted an opinion from climate scientists and
paleoclimatologists (scientists who study ancient climates) who were directly familiar
with the underlying issues.
Mann and Oppenheimer learned that a number of other colleagues, including Tom Wigley of
the University Corporation for Atmospheric Research (UCAR) in Boulder, Colorado; Philip
Jones of the University of East Anglia's Climatic Research Unit in Norwich, United
Kingdom; and Raymond Bradley of the University of Massachusetts in Amherst were
receiving similar media requests for their opinions on the matter. Their original
memorandum evolved into a more general position paper jointly authored by a larger group
of leading scientists in the field.
Mann says he sees the resulting Eos article as representing an even broader consensus of
the viewpoint of the mainstream climate research community on the question of late 20th
century warming and its causes. The goal of the authors, he says, is to reaffirm support
for the AGU position statement on climate change and greenhouse gases and clarify what
is currently known from the paleoclimate record of the past one-to-two thousand years
and, in particular, what the bearing of this evidence is on the issue of the detection
of human influence on recent climate change.
Notes for Journalists:
The article, "On Past Temperatures and Anomalous Late-20th Century Warmth. appears in
Eos, Volume 84, No. 27, 8 July 2003, page 256.
Authors (full list):
Michael Mann, University of Virginia, Charlottesville, Virginia;
Caspar Ammann and Kevin Trenberth, National Center for Atmospheric Research, Boulder,
Raymond Bradley, University of Massachusetts, Amherst, Massachusetts;
Keith Briffa, Philip Jones, and Tim Osborn, Climatic Research Unit, University of East
Anglia, Norwich, United Kingdom;
Tom Crowley, Nicholas School of the Environment and Earth Science, Duke University,
Durham, North Carolina;
Malcolm Hughes, Laboratory of Tree-Ring Research, University of Arizona, Tucson,
Michael Oppenheimer, Princeton University, Princeton, New Jersey;
Jonathan Overpeck, Department of Geosciences and Institute for the Study of Planet
Earth, University of Arizona, Tucson, Arizona;
Scott Rutherford, University of Rhode Island, Narragansett, Rhode Island;
Tom Wigley, University Corporation for Atmospheric Research and National Center for
Atmospheric Research, Boulder, Colorado.
Journalists may obtain a pdf copy of this article by request to Harvey Leifert
(hleifert@agu.org). Please provide your name, name of publication, phone, and email
AGU's position statement, Climate Change and Greenhouse Gases (1998), may be read at
[1]http://www.agu.org/sci_soc/policy/climate_change_position.html. A peer reviewed
article, discussing the scientific background to the position statement appeared in Eos,
Volume 80, No 39, September 28, 1999, page 453, and may be read at
Contact information for authors:
Harvey Leifert
Public Information Manager
American Geophysical Union
2000 Florida Avenue, N.W.
Washington, DC 20009, USA
Phone: +1-202-777-7507
Fax: +1-202-328-0566
Email: hleifertatXYZxyz.org
Web: [3]http://www.agu.org/sci_soc/media.html

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