Thought this might be of interest. dw
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From: tsocci@usgcrp.gov (Tony Socci)
Subject: July 20th US Global Change Seminar:"Reconstruction of the Earth's Temperature
Record for the Last Six Centuries: Are the Earth's Glaciers Responding
to Climate Change?"
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U.S. Global Change Research Program Seminar Series
Reconstruction of the Earth's Temperature Record for the Last Six Centuries:
Are the Earth's Glaciers Responding to Climate Change?
What is the "reconstructed" surface temperature record of the Earth for the
last six centuries and how does it compare to the recent IPCC
(Intergovernmental Panel on Climate Change) conclusions? Is the
temperature trend over the past six centuries consistent with natural
climate variability, or is the trend more likely due to causes outside of
(or beyond) natural climate variability, such as the activities of humans?
What is the status of the world's glaciers outside of the polar regions?
Is the observed glacial melting or retreat a response to observed climate
warming?
Public Invited
Monday, July 20, 1998, 3:15-4:45 PM
NEW LOCATION - Dirksen Senate Office Bldg., Room G11, Washington, DC
Reception Following
INTRODUCTION
Dr. Herman Zimmerman, Paleoclimate Program Director, National Science
Foundation, Arlington, VA
SPEAKERS
Dr. Michael E. Mann, Department of Geosciences, University of
Massachusetts, Amherst, MA
Dr. Mark F. Meier, Professor Emeritus, Department of Geological Sciences,
and Fellow of the Institute of Arctic and Alpine Research (INSTAAR),
University of Colorado, Boulder, CO
Reconstructing the Earth's Temperature Record
Assessing the significance of the global warming of the 20th century has
traditionally been hampered by a sketchy knowledge of climate variations
during past centuries. Widespread instrumental climate data are only
available during the 20th century (and even during this period, provides
nearly complete coverage only for the Northern Hemisphere and tropical
Southern Hemisphere). To go back much further in time, indirect
measurements of climate variations derived from natural archives or "proxy"
climate indicators such as tree rings, corals, and ice cores, must be used
to characterize climate variations.
By using modern statistical techniques to match the widespread
instrumental record of the 20th century to natural archives or "proxy"
climate indicators such as tree-ring, coral, and ice-core records, combined
with the suite of long historical climate records, global patterns of
annual temperature have been reconstructed several centuries back in time,
with relatively small uncertainties. These uncertainties have been
accurately estimated, providing a faithful assessment of the level of
certainty in reconstructions of the climate during past centuries. With
the longer term perspective afforded by this reconstructed climate history,
this reassessment of the Earth's temperature record provides an arguably
more robust assessment of recent global warming because of its long term
context. The evidence suggests that the decade of the 1990s, especially
the years 1990, 1993, and 1997, are almost certainly the warmest back to AD
1400 for the Northern Hemisphere as a whole. The El Nino phenomenon also
appears to have increased in intensity in recent decades relative to its
pre-20th century behavior. This trend is not, however, as dramatic as that
seen in hemispheric temperatures, and the evidence is more tentative given
the larger uncertainties inherent in reconstructing this phenomenon. The
reconstructed climate patterns were tested for their reliability through a
battery of statistical "verification" experiments which demonstrated that
the proxy-based climate patterns could reliably "predict" early thermometer
measurements. The success of the comparison provides compelling evidence
that the reconstructions can be trusted back in time. These tests also
indicated that, with the proxy data networks presently available, it is
difficult as yet to draw conclusions about global climate variations
further back in time than AD 1400.
The changes in hemispheric temperature over several centuries were related
to possible influences or "forcing agents" through comparisons with the
estimates of changes in the three most physically plausible external
factors governing climate change over time-changes in the brightness of the
Sun back in time as estimated by solar physicists, the documented history
of explosive volcanic eruptions, and human-caused increases in greenhouse
gas concentrations as represented through long-term records of carbon
dioxide trapped in ancient ice cores and more recently recorded by humans.
These comparisons sought to determine which of these three forcings of
climate were most closely related, in a statistical sense, to the
variations in hemispheric temperatures over time. The results of this
analysis suggests that the significant temperature variations in past
centuries likely have their origins in natural climate forcing - -
variations in the brightness of the Sun in particular. While these natural
factors will no doubt continue to play a role in governing the natural
climate variability that operates in the backdrop of human-induced changes
in climate, the anomalous warmth of recent decades cannot be explained in
terms of these natural factors. Instead, the recent warming shows a
sharply emerging significant correlation with increasing greenhouse gases
during the past couple of decades. In this sense, the human-enhanced
greenhouse warming signal now appears to be detectable above the background
of natural climate variability. The recent IPCC conclusion that the
"fingerprint" of human activity is discernible in the most recent climate
trends is consistent with independent studies that have compared
model-predicted and observed trends during the 20th century.
Changing Glaciers Indicate Changing Climate
Glaciers and ice caps have been retreating, thinning, and disappearing all
over the world during this century, interrupted by short periods of growth
in some areas. This recession (shrinkage) rate is now accelerating.
Glaciers are thought to be sensitive indicators of climate. This recession
therefore, is a tangible, highly visible indicator of a changing climate.
Glacier wastage also has direct environmental and societal impacts,
especially in regard to sea-level rise and river flow. A new mathematical
technique called "scaling", now allows characterization and generalization
of glacier changes on a global basis.
Current changes in the two huge continental ice sheets (Greenland and
Antarctica) are not fully understood, and are not considered here.
Instead, these analyses focus on the behavior of the 160,000 or so "small"
glaciers and ice caps that are of major importance as climate indicators,
and as sources of runoff that contribute to sea-level change.
What Do Measurements on the Glaciers Tell us about Climate?
Measurements of mass balance (snow input, minus melting and runoff output)
provide information on glacial (and climate) change, especially during the
period since the early 1960s when many observational programs began. These
data are important because they record changes in precipitation and
temperature in high mountains and at high latitudes where other data are
sparse. On a global basis, snow accumulation appears to be increasing
slightly, especially at higher altitudes. This implies a slight increase
in winter precipitation. However, melting rates are increasingly
significant, especially at lower altitudes, suggesting a major increase in
summer air temperature. Both data sets show increasing year-to-year
variability. Combining these data, the net mass balance of glaciers is
increasingly negative (snow or ice loss exceeds accumulation). On average,
the world's glaciers lost 0.18 meters (0.60 feet) per year of
water-equivalent of thickness from 1961 to 1990, and the rate of ice loss
has been increasing with time. This averaged trend of a net negative
glacial mass balance roughly follows the trend in the Northern Hemisphere
of increasing air temperatures, but there are many year-to-year
differences.
What is Happening to the Glaciers of the World?
Changes in size (length, thickness, volume) of glaciers are easier to
record than mass balance. In general, glaciers appear to have been equal
or larger than today during the 16th through 19th centuries, but with
numerous small fluctuations that are incompletely documented. Since 1900,
depending on the region, glacial recession (shrinkage) has been the rule
and the current recession rates are greater than those inferred during
earlier centuries. Compilations of area and volume change of the glaciers
in mid-latitude locations show major changes in the last 100 years: about
1/2 of the volume of glacier ice in the European Alps has disappeared since
the end of the 19th century. Nearly 1/4 of the ice in the glacier-covered
Tien Shan has been lost in the last 40 years. Similar data from the
Western Hemisphere does not exist, but some individual glaciers have been
studied. For instance, Grinnell Glacier, one of the larger glaciers in
Glacier National Park, decreased in area from 2.2 to 1.0 square kilometers
(0.9 - 0.4 square miles) from 1900 to 1981, and calculations indicate that
it will be gone in 50 to 70 years, and with it virtually all the glaciers
in this National Park. In other areas, some glaciers are rapidly
disappearing: in 1980, Spain boasted 27 glaciers; by 1994 the number was
down to 13.
By way of contrast, the ice caps and glaciers in the Arctic have changed
only slightly (e.g., a loss of 13% of their volume since 1880, in
Svalbard). The ice caps in the High Arctic of Russia and Canada decreased
only a few per cent in the last century. This phenomena begs some
explanation because studies by Lachenbruch, Overpeck, and others have
shown that the 20th century temperature rise in the Arctic and sub-Arctic
has substantially exceeded the global average. One reason for the
difference is that these glaciers are so cold that meltwater refreezes and
does not run off. Obviously, the glacier/climate relation shows strong
regional differences not simply related to air temperature; these have not
yet been well defined but the regional variations may aid our understanding
of the spatial pattern of climate change.
What are the Present and Future Implications of this Glacier Recession?
… Glacier studies are a useful adjunct to other proxy and instrumental
climatic studies because they reveal changes in precipitation and
temperature in parts of the world not covered by other observations. The
ability to infer climate change as it varies with altitude is especially
meaningful.
… Glacier recession and thinning in the 20th century are unprecedented,
according to this analysis, for at least a millennium. As such, they
provide tangible examples of the impact of climate warming to date.
… Glacial retreat, however, is destroying many of the paleoclimate records
housed in glacial ice, especially on high mountains at low latitudes.
… As glaciers thin and disappear, river flow in glacier areas is affected:
glacier wastage brings ice out of storage, temporarily adding to river
flow, but as glaciers disappear this extra increment of water disappears.
In addition, glacier-fed streams are naturally regulated so that glaciers
disappear, the year-to-year variability of stream flow will increase. In
addition to water supply, this will affect the local ecology.
… Glacier wastage has contributed about 20% of the observed rise in sea
level during the past century. Glacier mass balances are becoming
increasingly negative (with melting increasingly exceeding snow
accumulation), so this contribution will likely increase until the area of
glacier ice is appreciably reduced.
… The IPCC 1996 report suggests that glacier wastage may be expected to
contribute about 0.16 meters (0.53 feet) to the "best estimate" total
sea-level rise of 0.49 meters (1.61 feet) by the year 2100. The glacier
contribution estimate is, however, made with very simplistic models and
could be appreciably over- or under-stated.
… The natural beauty and the lure of many of our prime national parks and
other areas such as the Alps will be seriously altered by the loss of
glaciers.
Biographies
Dr. Michael E. Mann has a joint appointment as an Alexander Holleander
Distinguished Postdoctoral Fellow of the Department of Energy and as an
Adjunct Associate Professor of Geosciences at the University of
Massachusetts in Amherst. His research focuses on the application of
time-series and statistical techniques to understanding climate variability
and climate change from both empirical and climate model-based
perspectives. A specific area of current research is paleoclimate data
synthesis and statistically-based climate pattern reconstruction during
past centuries using climate "proxy" data networks. A primary focus of
this research is empirically deducing the long-term behavior of the climate
system and its relationship with possible external (including
anthropogenic) "forcings" of climate. His other areas of active research
include model-based simulation of natural climate variability, climate
model/data intercomparison, and long-range climate forecasting.
Dr. Mann is the author of approximately 30 peer-reviewed journal
publications or book chapters. His work on global climate change has been
widely described in the popular media, including ABC, CBS, NBC, and CNN
news programs, Time Magazine, US News and World Report, NPR, The Economist,
BBC, USA Today, and has been featured in stories in the New York Times, the
Boston Globe, and numerous other U.S. and international news publications.
He has also served as a consultant to the private sector regarding
potential societal impacts of climate change, and is frequently sought out
by international scholarly journals as an expert in the area of statistical
data analysis applied to the physical sciences.
Dr. Mann received his undergraduate degrees in Physics and Applied Math
from the University of California at Berkeley, an MS degree in Physics from
Yale University, and a Ph.D. in Geology & Geophysics from Yale University.
Acknowledgments: The research presented in this seminar derived primarily
from a recently published article in the journal "Nature" (v. 392, pp.
779-787, 1998) co-authored with collaborators Raymond Bradley of the
University of Massachusetts and Malcolm Hughes of the University of Arizona
Tree Ring Research Lab, and from a chapter by the same authors, to appear
in a book on El Nino published by Cambridge University Press. This
research has been funded by the National Science Foundation and the
Department of Energy.
Dr. Mark F. Meier is Professor Emeritus in the Department of Geological
Sciences and Fellow of the Institute of Arctic and Alpine Research
(INSTAAR) at the University of Colorado. He has served on many panels and
committees of the National Research Council (NRC), National Science
Foundation, and international organizations, including the NRC committee
that formulated the International Geosphere-Biosphere Program. He was a
Lead Author for the Sea Level Changes chapter of the 1995 IPCC Scientific
Assessment, former Director of INSTAAR, first Director of the National Ice
Core Lab, founder and head of the U. S. Geological Survey's Glaciology
Office, President of the International Commission on Snow and Ice,
President of the International Association of Hydrological Sciences,
President of the International Union of Geodesy and Geophysics, and
Chairman of the Board and President of the Arctic Research Consortium of
the U. S.
Dr. Meier received his B.S. and M.S. degrees in Electrical Engineering and
Geology from the University of Iowa, a Ph.D. in Geology and Applied
Mechanics from the California Institute of Technology, and did post-Ph.D.
(Fulbright grant) work in meteorology and geophysics at the University of
Innsbruck, Austria. He has published about 200 scholarly articles, and has
been the recipient of several medals and other honors.
Acknowledgments: This seminar is derived from Dr. Meier's long interest in
glacier mass balances, sea-level rise, and global change. Most recently he
has had valued collaboration with Drs. David Bahr and Mark Dyurgerov at
INSTAAR. This work has been financed by the National Science Foundation
and the Department of Energy.
The Next Seminar is scheduled for Monday, September 21, 1998
Tentative Topic: Ozone Depletion and the Montreal Protocol:
Historic Trends, Present Status, and Future Projections.
For more information please contact:
Anthony D. Socci, Ph.D., U.S. Global Change Research Program Office, 400
Virginia Ave. SW, Suite 750, Washington, DC 20024; Telephone: (202)
314-2235; Fax: (202) 488-8681 E-Mail: TSOCCI@USGCRP.GOV.
Additional information on the U.S. Global Change Research Program (USGCRP)
and this Seminar Series is available on the USGCRP Home Page at:
http://www.usgcrp.gov. A complete archive of seminar summaries can also be
found at this site. Normally these seminars are held on the second Monday
of each month.
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