Alaska Forests in Danger from Warming
12/8/97
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RELAYED TEXT STARTS HERE:
Headline: Alaska Forests in Danger from Warming
Source: 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.
Date: 12/8/97
U.S. Global Change Research Program Seminar Series
Observed Climate Change in Alaska: The Early Consequences of Global Warming
What is the evidence that Alaska has warmed over the last century? Are
these observed changes consistent with climate model projections of
human-induced changes? What are the observed impacts and consequences of
these changes in climate, with respect to society and ecosystems? What
further consequences will occur from changes projected for the future?
Public Invited
Monday, December 8, 1997, 3:15-4:45 PM
Rayburn House Office Bldg., Room B-369, Washington, DC
Reception Following
INTRODUCTION
David A. Kirtland, National Assessments Coordinator, U.S. Department of the
Interior, Reston, VA
SPEAKER
Glenn Patrick Juday, Associate Professor of Forest Ecology, Forest Sciences
Department, University of Alaska-Fairbanks, Fairbanks, AK
OVERVIEW
Alaska is approximately one-fifth the area of the 48 contiguous
states. This large domain encompasses several distinct climatic and
ecological regimes, and includes nearly 80% of U.S. public lands. There
are approximately 114 million acres of forest in the northern interior
region of Alaska (Fairbanks region), and an additional 12.5 million acres
of forest along Alaska's rainy Pacific coastal region (Anchorage and
southeast Alaska region).
Results from several studies at the Bonanza Creek Long-Term Ecological
Research (LTER) site, as well as research results from elsewhere in Alaska,
provide unambiguous evidence of a significant climate warming over the past
century. Observational records of climate change dating back to the early
20th century are currently available for just a few localities in Alaska.
However, tree-rings and other proxy indicators of climate change are being
used to supplement the instrumental records and to help reconstruct climate
trends in Alaska prior to the 20th century.
These climate records indicate that Alaska experienced a major shift toward
warmer conditions in the late 1970s, as did much of the world. As a
result, the climate in the northern interior (Fairbanks region) and coastal
forest regions (Anchorage region) of Alaska is now warmer than at any time
in the last several centuries and very probably the last millennium. The
magnitude of this recent shift, as well as the rate of climate warming and
projected future changes, pose a host of problems and opportunities for the
people of Alaska, quite often having international economic implications as
well. Such changes are also impacting the infrastructure presently in
place, and may affect the chances of survival of forest and other
ecosystems of Alaska, the goods and services of which are crucial to the
region.
The observed changes in climate in Alaska are generally consistent with the
projections from climate models that have been used to simulate the warming
effect of increasing greenhouse gas concentrations in the atmosphere. In
particular, the model results project that high latitude land areas of the
Northern Hemisphere would experience the most rapid and largest warming on
Earth.
Climate Changes Are Affecting the Forest Ecosystems of Alaska
Interior Alaska - Fairbanks Region
Tree-ring records indicate that northern and central Alaska is warmer now
than at any time since medieval warm interval of about 1000 A. D. The
observed mean annual temperature of the northern interior region of Alaska
in the vicinity of Fairbanks has increased about 1.4 YC (2.6 YF) during the
20th century. Records indicate that the climate warmed in this region from
1850 to 1940, then cooled from 1941 to 1975, and has warmed significantly
since 1976. The warming from the mid 1970s to the mid 1990s averaged 1 YC
per decade, totaling about 3 YC over this period. In addition, summer
precipitation has decreased at the rate of about 17% per hundred years
during the period of record in the Fairbanks area. Snowfall totals at
Fairbanks, on the other hand, are up about 60% during the 20th century;
substantially greater increases have occurred on the south-facing mountain
slopes that intercept moisture-bearing winds from the Pacific. Heavy snow
loads appear to be a major factor in tree canopy breakage. Injured pockets
of trees attract wood-boring insects that can build up in numbers and, if
climate conditions are favorable, cause widespread tree death, with
far-reaching ecological and social consequences.
The growth of low-elevation forests in the interior of Alaska is directly
limited by summer warmth and moisture deficit, as indicated by an analysis
of the physical and chemical properties of tree-rings. The results
indicate that the last 20 years have been the least favorable period for
the growth of white spruce trees in the 20th century, and almost certainly
for the last 400 years. Tree growth in these white spruce forests has been
reduced by 50% in some cases, and growth of paper birch has significantly
declined as well. There are many new instances of insect infestation of
stressed trees; and spruce cone crops at various places have either not
occurred or are so low as to not provide the numbers of seeds necessary for
effective reproduction. Furthermore, the total area burned by forest fires
in Alaska is directly related to summer temperature, and the incidence of
fires would be expected to increase as summer temperatures increase.
Coastal South-Central Alaska - Anchorage Region
Mean annual and mean summer temperatures at Anchorage in coastal
south-central Alaska have warmed at a rate of about 1.6 YC (3 YF) per
century during the 20th century. Unlike the interior Fairbanks region of
Alaska, however, precipitation at Anchorage has increased at a rate of
about 23% per century. Accordingly, white spruce trees in the Anchorage
and south-central Alaska regions have experienced strongly accelerated
growth that is directly correlated with the warmer and moister conditions.
However, one of the largest outbreaks of insect-caused (spruce bark beetle)
tree mortality in the history of North America has left most trees dead
over about 3-million acres of forest land. Spruce bark beetle populations
have historically been limited or kept in check by cool summers and cold
winters, so rising temperatures (the most likely cause of the beetle
outbreak) have not been beneficial in this case. Commercial forest value
and many of the non-market values (e.g., recreational value) have been
dramatically reduced over most of the region.
Southeastern Alaska
The sitka spruce - western hemlock rainforest of southeast Alaska is highly
valued for timber, wildlife and fisheries habitat, and as the setting for
rapidly expanding tourism and wilderness recreation. In southeast Alaska,
the number of days with gale-force winds have more than doubled since 1950,
increasing the risk of extensive tree blowdown. Warmer summer weather and
extended rainless intervals have triggered outbreaks of the defoliating
western black-headed budworm, and apparently have increased the number and
duration of low stream flow episodes; it is these conditions that block the
return of spawning salmon and generally limit municipal and industrial
water supplies.
Climate Changes Affecting the Snow, Ice, Soils, and Permafrost
In all but the climatically mildest coastal section of the southeastern
panhandle region, Alaska remains frozen for half or more of the year. Most
of Alaska is underlain by soil that remains permanently frozen
(permafrost). Snow, ice, and frozen soils are an extremely important part
of both the natural environment and human-occupied settlements. The
warming observed in the 20th century is having a number of effects:
. Three of the four earliest spring break-ups of ice on the Tanana River
have occurred in the 1990s, the warmest decade in the 81-year record.
. Even with warmer conditions in winter, temperatures remain below
freezing. Thus, as the climate in Alaska has warmed, snowfall has
generally increased as the moisture-holding capacity of the atmosphere has
increased.
. Soil temperature in cold regions is controlled primarily by the mean
annual temperature and the insulating effect of snow (depth and duration).
The combination of increased annual temperature and increased snowfall in
the past 20 years has tended to rapidly increase the temperature of most of
the soil and permafrost in central and southern Alaska. Warmer soils speed
up the reactions that decompose stored soil organic matter, thus causing a
net release of CO2 to the atmosphere that adds to the greenhouse effect.
. Model studies and field measurements of soil temperature at the Bonanza
Creek Long-Term Ecological Research (LTER) site indicate that, for most of
the discontinuous permafrost in that region, the seasonally-thawed soil
layer above the permanently frozen soil layer is penetrating more deeply in
recent years, leaving the remaining permanently frozen soil below very
close to the thaw point, much of it only a few tenths of a degree YC below
freezing.
. Nearly all permanently frozen soil contains ground ice masses that when
thawed lead to surface subsidence. Roads and structures built on
permafrost can suffer severe damage from thaw-related subsidence. Most
structures have been built to withstand a certain amount of permafrost
thawing which always accompanies site disturbance; but the recent warming
frequently exceeds structural design limits. Subsidence features in
natural environments often collect water from the melting of ice in soils,
which greatly speeds up the transfer of heat to the soil. Thawed
subsidence sites also often change from black spruce woodland ecosystems to
wetland, potentially increasing the release of methane during the
decomposition of soil peat. Thaw-related subsidence is becoming more
noticeable in central Alaska as well. In fact, extensive areas of Alaska
are projected to undergo thaw-related subsidence with only slightly more
warming.
Biography
Dr. Glenn Patrick Juday is currently Associate Professor of Forest Ecology
in the Forest Sciences Department at the University of Alaska-Fairbanks. He
has been active in the field of global change research for over 17 years.
His research interests include the analysis of tree rings as indicators of
climatological and ecological changes and study of the ecological effects
of climate change, biodiversity and forest management, old-growth forest
ecosystems, and the management of wilderness and other natural areas. His
most recent research has focused on the responses of trees to climate
change in Alaska.
Dr. Juday is currently the Chair of the Society of American Foresters
Forest Ecology Working Group. He is also currently coordinating a
synthesis of results on the ecological effects of climate change across the
entire network of Long-Term Ecological Research sites nationwide. Dr.
Juday is the author of an extended Encyclopedia Britannica article on
Boreal Forests (1995 edition) and was science advisor for the Discover
Channel TV Program "Glaciers, Rivers of Ice" (1994), and a European TV
documentary on the effects of global warming on Alaskan forests, produced
by the Danish Broadcasting Corporation (1997). He has served as a
consultant (in residence) to the National Science Programs office of The
Nature Conservancy and was a member of the scientific steering board for
the Exxon Valdez Oil Spill Restoration program.
Dr. Juday received his undergraduate degree in Forest Management from
Purdue University (1972) and his Ph.D. from Oregon State University in
Plant Ecology (1976). He was later awarded a Rockefeller Foundation
post-doctoral fellowship in environmental affairs in 1977. He and his
family have resided in Alaska for 20 years.
Acknowledgments: The data presented in this seminar represent a synthesis
of Dr. Juday's own work as well as the work of several investigators at the
Bonanza Creek LTER site and the Lamont-Doherty Tree-Ring Laboratory.
The Next Seminar is scheduled for Monday, January 19, 1998
Planned Topic: Methane - Society's Second Most Important Greenhouse Gas
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. Normally these seminars are held on the second
Monday of each month.