You woodies on the east coast get all the good stuff! Cheers, Dave
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From: Tony Socci <tsocci@usgcrp.gov>
Subject: December 8, 1998 US global Change Research Program Seminar:
"Changes in Carbon Sources and Sinks: The Outlook for Climate Change and
Managing Carbon in the Future"
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U.S. Global Change Research Program Seminar Series
Changes in Carbon Sources and Sinks: The Outlook for Climate Change and
Managing Carbon in the Future
What are the observed and projected trends in CO2 emissions and atmospheric
concentrations of CO2? How would these levels compare to past levels of
CO2 the Earth has experienced? What is the potential for the ocean and the
terrestrial biosphere to absorb atmospheric CO2 and thus reduce the
potential for climate warming? Are sources and sinks for CO2 permanent or
are they dependent on the state of the climate system at any one time? Can
carbon be managed or stored on a long-term or short-term basis?
Public Invited
Tuesday, December 8, 1998, 3:15-4:45 PM
Temporary Location: Rayburn House Office Bldg., Room B-369
Washington, DC
Reception Following
INTRODUCTION
Elliott Spiker, Coordinator, Global Change and Climate History Program,
Department of the Interior, U. S. Geological Survey, Reston, VA
SPEAKERS
Dr. Pieter Tans, Chief Scientist, Climate Monitoring and Diagnostics
Laboratory of the National Oceanic and Atmospheric Administration, Boulder,
CO
Dr. Jorge L. Sarmiento, Atmosphere-Ocean System Program, Princeton
University, Princeton, NJ
Dr. William H. Schlesinger, James B. Duke Professor, Department of Botany,
Duke University
Durham, NC
Natural Variations of the Global Carbon Cycle and Human Influence
The unrestrained burning of the Earth's conventional fossil fuel resources
during the next few hundred years has the potential to increase the
atmospheric CO2 concentration to more than ten times the pre-industrial
concentration of CO2. The main difference between a rapid burning of
fossil fuels and a scenario in which CO2 emissions would be capped at 1990
rates is that the latter affords more time to develop alternative sources
of energy before the concentration of atmospheric CO-2 can reach such high
levels. In terms of climate change, such an atmospheric loading would
produce a human-induced climate forcing of more than 12 watts per square
meter (W/m2), roughly five times the present forcing of climate (warming)
due to the human-induced enhancement of greenhouse gas concentrations.
This estimate assumes that the rest of the climate system (water vapor,
clouds, snow and ice cover, etc.) remains unchanged. Climate feedbacks
would probably amplify or possibly reduce this figure to some extent, and
thus the role and magnitude of various feedbacks are the subjects of
on-going inquiry and discussion. Currently CO2 alone is responsible for a
climate forcing (warming) of 1.4 W/m2, while the combination of all
long-lived greenhouse gases account for a climate forcing of about 2.3-2.5
W/m2, and this level is growing. For comparison, the estimated possible
changes in solar output during the last few centuries are up to 0.5 W/m2.
Increased CO2 has not only atmospheric effects, but such elevated levels of
atmospheric CO2 will also significantly alter the chemistry of sea water,
rendering it more acidic, for example.
The fact remains that the concentration of atmospheric CO2 will continue to
rise even if society elects to keep global CO2 emissions constant
indefinitely. Nature re-distributes carbon among the three reservoirs, and
it is very likely that the concentration of atmospheric CO2 will remain
elevated for hundreds of years and probably thousands of years. In
addition, the climate itself will influence how carbon is partitioned among
the three reservoirs. In a warmer world, for example, Arctic permafrost
soils may thaw, releasing large quantities of CO2 to the atmosphere.
The Potential for Carbon Management and Storage in Terrestrial Ecosystems
A number of independent lines of evidence support the idea of the existence
today of large terrestrial sinks of CO2. The mechanisms by which these
sinks operate are not yet sufficiently understood, and thus, there is
uncertainty as to how such sinks will operate in the future under an
altered climate. There is uncertainty as well as to the permanency of
carbon sinks. For example, present and future sinks for CO2 might become
sources of CO2 if the climate were to change significantly. However, the
existence of such large sinks for CO2 also suggests that there might be
ways to manage natural systems to store additional carbon and therefore,
mitigate climate warming to an as yet unknown extent.
Implications of the Exchange of CO2 between the Atmosphere and the Ocean
Of the carbon not taken up by terrestrial ecosystems, the ocean will be the
eventual repository for about 85% of the rest of the carbon emitted to the
atmosphere by human activities. This estimate of uptake capacity is based
on well-understood physical and chemical processes. However, this uptake
occurs quite slowly. For example, the ocean is presently taking up only
40% (with an uncertainty of plus or minus 16%) of the annual anthropogenic
carbon emissions not removed by terrestrial processes. Because of the slow
rate of mixing of the ocean, it would take many centuries for the ocean to
realize most of its uptake capacity, even if anthropogenic emissions were
to stop today. An additional 5-10% of the anthropogenic atmospheric carbon
emitted today will be taken up by the ocean by the reaction of excess
oceanic CO2 with limestone in ocean sediments, but this occurs on a time
scale of millenia.
Calculations of the rate of uptake of anthropogenic carbon by the oceans
require the use of carefully formulated ocean circulation models. A major
contribution to our confidence in such models is our ability to calibrate
them using observations of a wide variety of tracers of ocean circulation,
as well as direct observations of ocean carbon inventory changes. However,
future predictions must take into account the warming of ocean waters
(which reduces the oceans capacity to absorb CO2 and other gases),
reductions in ocean mixing (which reduces the rate at which the oceans can
absorb CO2 and other gases), and changes in biology that will likely take
place as a result of global warming. A number of recent studies with
coupled atmosphere/ocean models of climate suggest that the impact of
global warming will likely reduce the oceans capacity to absorb CO2 and
other gases by about 10% to 30% by the middle of the next century, but
further research is needed. A major concern raised by such models is the
possibility that environmental changes will also have a substantial impact
on ocean ecology.
Models of the ocean carbon system are also required in order to estimate
the possible contribution of the ocean to absorb atmospheric carbon and
thereby moderate future atmospheric growth rates.
Such models indicate that the efficiency of permanent sequestration in
reducing the atmospheric increase in CO2 between now and the middle of the
next century would be about 75% if only the ocean is considered, but may
drop to only about 60% using one particular model of the terrestrial
biosphere. The ocean's efficiency to absorb atmospheric CO2 is also
sensitive to the model scenario utilized to project the ocean's capacity to
sequester carbon; the scenario used in this analysis is a gradually
increasing rate of sequestration over the time period considered. If, for
example, sequestration is confined to the ocean alone, some of the
sequestered CO2 will eventually escape to the atmosphere, reducing the
efficiency of the ocean to absorb CO2 even more, although this effect can
be minimized by sequestering the CO2 in waters that are relatively isolated
from mixing.
A major focus of recent ocean carbon research has been aimed at determining
the spatial and temporal distribution of exchanges of CO2 between the
atmosphere and the ocean. Such research is essential for understanding the
basic mechanisms that determine the cycling of carbon within the ocean, and
also for combining with atmospheric CO2 observations to constrain the
location of the terrestrial carbon sink. One recent estimate of the
terrestrial carbon sink suggests that there was a surprisingly large uptake
of CO2 in North America during the period from 1988 to 1992. This study
also identified additional measurements that would help to improve the
confidence in such estimates and improve their spatial resolution.
Response of Vegetation to Rising Carbon Dioxide
At the present time, two processes may lead to a net storage of carbon in
vegetation and soils. The first process is the regrowth of vegetation on
land that is abandoned from agriculture. The second is the likely positive
response of plants to fertilization because of the rising CO2
concentration and the deposition of atmospheric nitrogen. Because CO2 is
one of the primary reactants for photosynthesis, a rising CO2 concentration
may stimulate the rate of photosynthesis and plant growth wherever
vegetation occurs. An important sink for carbon in North America derives
from the regrowth of plants on abandoned agricultural land. Despite
hundreds of studies in greenhouses, however, much less is known about the
potential sink for carbon due to the direct plant response to CO2 in
natural ecosystems. And, there is good reason to suspect that plant
responses in simulated greenhouse conditions may differ from those found in
nature, where soil, water and nutrients may be in short supply and thus,
limit growth. Understanding the response of vegetation to rising CO2 is a
critical component of global change research, because the sink for carbon
on abandoned land is finite; it will cease when the vegetation has matured
on these lands.
A recent experiment was undertaken to study the response of vegetation to
rising atmospheric CO2 concentrations using a technique known as Free Air
CO2 Enrichment (FACE), developed at Brookhaven National Laboratory. FACE
experiments allow one to expose large plots of forest, desert, grassland or
other vegetation to constant, high levels of CO2 with minimal disruption of
light, microclimates, and soil conditions that often determine the growth
of plants. In the Duke Forest in central North Carolina, a FACE
experiment was initiated in late 1996 to examine the growth of 15-year-old
loblolly pine trees when subjected to a CO2 concentration of 560 ppm (parts
per million) - the concentration that is anticipated globally, as early as
the middle of the next century. Loblolly pine was selected because it is
one of the fastest growing tree species and should, therefore, exhibit a
significant growth response under conditions of elevated CO2.
The first year (1997) of this experiment witnessed a 12% increase in the
growth of these trees above ground. Preliminary results for the second
year (1998) of this experiment show a lesser increase in growth rate, but
the trees subjected to high CO2 remain larger than the trees in the control
plots. The proportional response below ground was somewhat larger, although
the absolute amount of plant tissue below ground is rather small. By July
1998, investigators found 68.9 grams of carbon per square meter in the
production of live and dead roots in control plots and 109.2 grams per
square meter in experimental plots. These results suggest that it is the
plant tissues above ground, rather than soils, that are more likely to act
as a sink for atmospheric CO2.
If this kind of response were to apply to forested land globally,
calculations indicate that about 20% of the fossil fuel use expected in the
year 2050 might be stored in forests and their soils. While helpful to the
problem, this storage (about 3 GtC/yr - gigatons of carbon per year) is
much smaller than many have speculated; thus, a large fraction of the CO2
released from fossil fuel combustion may well remain to accumulate in the
atmosphere. Moreover, it is likely that the response of vegetation will
decline with time, as soil nutrients become depleted. For example, the
growth of trees near some CO2-emitting springs in Italy is stimulated only
during the first few years of their life.
In considering potential risks of CO2 build-up, decision-makers might well
anticipate other large changes in the terrestrial biosphere as the climate
changes. For example, should rising CO2 concentrations lead to a
significant global warming, particularly in northern ecosystems, soils may
become a large additional source of CO2 to the atmosphere due to more rapid
rates of decomposition in warmer soils. Recent observations of spruce
trees in Manitoba, Canada show a much greater emission of CO2 from soils in
warmer years, such that the forest is a net source of CO2 to the atmosphere
adding to the concentration of greenhouse gases already present in the
atmosphere.
Biographies
Dr. Pieter Tans is Chief Scientist at the Climate Monitoring and
Diagnostics Laboratory of the National Oceanic and Atmospheric
Administration in Boulder, Colorado. He has researched the global carbon
cycle for several decades, starting with his Ph.D. dissertation research in
the Netherlands, and has published about 100 scientific papers on the
subject. His group maintains the world's largest global monitoring network
of atmospheric greenhouse gas concentrations. Isotopic ratios of several
of the greenhouse gases are also measured. From these data temporal trends
and large-scale spatial patterns are derived of the sources and sinks of
greenhouse gases such as carbon dioxide and methane. The latter effort
requires the use of atmospheric and chemical circulation models.
Dr. Tans has served on the Committee on Oceanic Carbon and the Panel on
Climate Variability on Decade to Century Time Scales, of the National
Research Council. He is also a member of the inter-agency Carbon and
Climate Working Group, associate editor of the Journal of Climate, and a
member of the editorial board of Tellus.
Dr. Jorge L. Sarmiento is a Professor of Geological and Geophysical
Sciences at Princeton University, Princeton, New Jersey. Dr. Sarmiento's
primary research interests are focused on oceanic cycles of climatically
important chemicals such as carbon dioxide, and on the use of chemical
tracers to study ocean circulation. He has published widely on ocean
tracers and the ocean carbon cycle, its history, its ongoing and potential
future perturbations by mankind, and its relationship to climate change.
On-going research includes the use of ocean general circulation models
(GCMs) to estimate uptake of anthropogenic CO2, and the use of atmospheric
general circulation models constrained with atmospheric CO2 observations to
estimate transport of CO2 in the atmosphere and carbon sinks in the
terrestrial biosphere. Dr. Sarmiento is working in conjunction with ocean
biologists to develop ecosystem models for predicting photosynthetic uptake
of carbon in the surface ocean, as well as remineralization of organic
matter in the deep ocean. He is also using coupled atmosphere-ocean models
of climate warming to study the impact of anthropogenic climate warming on
the global carbon cycle.
Dr. Sarmiento has participated in the scientific planning and execution of
many of the large-scale, multi-institutional and international
oceanographic, biogeochemical and tracer programs of the last two decades.
He has served on the Climate Research Committee and Committee on Oceanic
Carbon of the National Research Council, as well as on the Advisory
Committee of Ocean Sciences of the National Science Foundation. He is the
Project Coordinator of the Carbon Modeling Consortium, a
multi-institutional program to study the anthropogenic carbon transient; he
is co-chair of the Synthesis and Modeling Project of the Joint Global Ocean
Flux Study; and he is co-chair of the Carbon and Climate Working Group that
is presently putting together a plan for U.S. carbon cycle research.
Dr. William H. Schlesinger is James B. Duke Professor in the Department of
Botany at Duke University, and he holds a joint appointment in the Division
of Earth and Ocean Sciences of the Nicholas School of the Environment.
Upon completing his A.B. degree at Dartmouth (l972) and his Ph.D. at
Cornell (l976), he joined the faculty at Duke University in 1980. He is
the author or co-author of over 120 scientific papers and the widely
adopted textbook "Biogeochemistry: An Analysis of Global Change" (Academic
Press, 2nd ed. l997). He was also elected as a member of the American
Academy of Arts and Sciences in 1995.
Currently, Dr. Schlesinger's research is focused on the role of soils in
the global carbon cycle. He is the principal investigator for the Free Air
Carbon Dioxide Enrichment (FACE) Experiment in the Blackwood Division of
the Duke Forest-a project that aims to understand how an entire forest
ecosystem (vegetation and soils) may likely respond to elevated CO2
concentrations. He has also worked extensively in desert ecosystems and
their response to global change, and is currently serving as Principal
Investigator for the NSF-sponsored program of Long Term Ecological Research
(LTER) at the Jornada Experimental Range in southern New Mexico.
Dr. Schlesinger has testified before U.S. House and Senate Committees on a
variety of environmental issues.
The Next Seminar is scheduled for Wednesday, January 20, 1999
Tentative Topic: State of Marine Ecosystems and Habitat
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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