Download Projected Climate Change and the Appalachian Trail

Prepared for ATC by Lenny Bernstein
Topic 7 - What impacts will projected climate change have on the A.T.?
“Making predictions is very difficult, especially about the future.”
Attributed to Yogi Berra
Before we can discuss how climate change will affect the A.T., we need an estimate of how
much climate will change. Climate scientists are reluctant to predict future climate because such
predictions depend on future greenhouse gas emissions, which depend on the future path of
human development. How many people will there be? How wealthy will they be? How much
energy will they use and what will be the sources of that energy? Instead, climate scientists refer
to their calculations of potential future climate as “projections” to indicate that they are
dependent on a specific set of assumptions and a specific climate model. See Appendix I for
more on how projections of future climate are developed.
The Nature Conservancy, the University of Southern Mississippi, and the University of
Washington have developed a tool called Climate Wizard (www.climatewizard.org) that presents
historical average (1951-2006) climate and the results of climate model projections for areas in
the U.S. as small as five mile square (25 square miles). Climate Wizard can use any of three
models or their average, and any of three emission scenarios, a total of twelve separate estimates
of future climate. Climate Wizard’s range of climate models and CO2 emission scenarios are
described in Appendix I. Each Climate Wizard projection of future climate includes annual and
seasonal average changes in temperature and precipitation.
The Nature Conservancy has provided the ATC with the information necessary to run Climate
Wizard for a band five miles on either side of the A.T. As an example of Climate Wizard results,
Figure 12 shows historical average annual temperature over the A.T. Appendix II presents
Climate Wizard’s results for three cases:
1. historical (1951-2006) climate,
2. moderate climate change, based on the climate model in Climate Wizard that gives results
closest to the IPCC’s best estimate of the impacts of CO2 on climate and a medium estimate
of future CO2 emissions, and
3. more extreme climate change, based on the climate model in Climate Wizard that projects
the highest impact of CO2 emissions and the emissions scenario that gives the highest level of
CO2 emissions.
Appendix II shows historical annual average temperature and precipitation over the A.T., as well
as the summer and winter averages. For the two climate change cases, Attachment II shows
projected changes in annual average, summer, and winter temperature and precipitation.
Figure 12 – Annual Average Temperature over the A.T. (1951-2006)
Data source: Climate Wizard, Map by Matt Robinson, ATC
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How Much Climate Change Will the A.T. Experience?
Moderate Case
For the moderate climate change case, annual average temperature is projected to rise about 2oC
(3.6oF) by 2041-2060 over the full length of the A.T., somewhat more at the northern end of the
Trail, and somewhat less at the southern end of the Trail. The seasonal projections show the
southern half of the Trail warming by about 3oC (5.4oF) in the summer, but only by about 1oC
(1.8oF) in the winter. The pattern is reversed on the northern part of the Trail with less summer
warming and more winter warming. If this projection is correct, the Trail in New Hampshire and
Vermont would experience summer temperatures similar to the historical average for New York
and New Jersey, while from New York south, summer temperatures would be warmer than the
historical average for any part of the Trail.
Climate Wizard projects small increases in annual average precipitation, about 50 mm (2 inches)
per year, over the Trail from Central Virginia north, but no change or a slight decrease in
precipitation from Southwest Virginia south. Summer rainfall is projected to decrease slightly
from Southwest Virginia south and over the Vermont and New Hampshire. Winter precipitation
(rain and snow) is projected to increase slightly over the full length of the Trail.
The projection of rising temperature, only modest increases in annual average precipitation, and
decreases in summer precipitation, would result in the Trail being drier than the historical
average, even in those areas that are projected to get more precipitation. Many parts of the Trail
could experience drought.
More Extreme Case
The more extreme case assumes that CO2 emissions will be 25% higher and that CO2 emissions
will have a 30% greater impact on climate than in the moderate case. These assumptions result in
2041-2060 temperatures that are 2.5-4oC (4.5-7.2oF) higher than the 1951-2006 historical
average over the entire A.T. The summer and winter temperature projections are similar to the
annual average projection. If this projection is correct, the summer temperatures along the whole
A.T. would be warmer than the historical average at the southern end of the Trail.
The biggest difference between the moderate and more extreme cases is the projected change in
precipitation. The more extreme case projects drier conditions over most of the A.T., and
severely drier conditions over the southern end of the A.T. From the Smokies south, the more
extreme case projects 200 mm (8 inches) less precipitation per year. The loss of precipitation is
more severe in the summer with the Trail as far north as Vermont receiving less rainfall. This
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combination of higher temperature and reduced summer rainfall would probably result in
permanent drought for most of the A.T.
Impacts on the A.T.
No single climate projection can be taken as an accurate forecast of future climate. Climate
models are not that precise, and even if they were, there is great uncertainty about the level of
future CO2 emissions. However, both from basic climate science and the range of climate model
projections, it is clear that unless future CO2 emissions are much lower than current projections,
the world in general, and the A.T. in specific, will experience significant temperature increases
and significant changes in precipitation patterns.
Climate change would create three types of impacts on the A.T.:
1. changes in the hiker experience;
2. changes in the distribution of birds, animals and plants inhabiting the A.T. corridor; and
3. changes due to more extreme climate
Changes in the Hiker Experience
Hiking the A.T. is a physically demanding activity, and higher summer temperatures would
create new challenges for hikers. It is likely that A.T. use would decrease during the hottest parts
of the summer.
Water availability could become a serious problem. Water availability is determined by the
amount of precipitation that falls and the rate at which it either runs off or evaporates. Higher
temperatures mean more evaporation. Without a significant rise in precipitation, they would lead
to more frequent drought conditions over the A.T. The moderate case projects small rises in
summer precipitation over the A.T. from Central Virginia northward, but no increase or a small
decrease in precipitation south of there. This would certainly result in reduced water availability
for the southern portion of the A.T., and could lead to frequent repeats of the conditions
experienced in Fall, 2007, when all water sources on the A.T. in the 90 miles north of Great
Smoky Mountains National Park went dry. As a result, Carolina Mountain Club had to
recommend against backpacking that section of the A.T. until there was significant rainfall. The
combined temperature and precipitation changes projected for the southern half of the A.T. in the
more extreme case would probably create almost permanent drought conditions and could make
backpacking the A.T. much more of a challenge.
It is well documented that, as a result of the warming of the 20th century, many species of plants
are flowering up to two weeks earlier. While we are not aware of any scientific studies, there is
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strong anecdotal evidence that A.T. thru-hikers have also responded to the warming of the last
few decades and are beginning their hikes earlier than the traditional early April starting date.
The A.T. “walking with Spring” experience seems to be adjusting to an earlier Spring.
Changes in the Distribution of Plants and Animals Inhabiting the A.T. Corridor
The habitats of plants and animals are largely determined by temperature and precipitation.
The critical factors may be the temperature and precipitation at a specific time of year, not the
annual average.
Plants and animals can respond to warming temperatures by migrating northward or to higher
elevations. Animal migration is obvious, since animals are mobile. Plant migration is less
obvious. Individual plants and trees cannot migrate, but the range over which they can propagate
can change. For both plants and animals, the ability to migrate is limited by that availability of
migration corridors, routes that are not blocked by human development, or other impassable
barriers, and suitable habitats. The A.T. may create a corridor for plant and animal migration, but
no guarantee that they will find suitable habitats.
The warming of the last 45 years has already caused trees to migrate up mountains to higher
elevations in New England. Scientists have made detailed comparisons of tree species at 2600
feet elevation at locations on Camel’s Hump, Mount Abraham and Bolton Mountain in the
Vermont’s Green Mountains, north of the A.T. In 1964, the forest at this elevation was 57%
northern hardwoods (sugar maple, yellow birch, and beech) and 43% boreal species (red-spruce,
balsam fir, and heart-leaved paper birch). By 2004, the forest was 82% northern hardwoods and
only 18% boreal species.
The transition zone between northern hardwood forest and boreal forest moved nearly 400 feet
upslope on Camel’s Hump between 1962 and 2005; nearly 300 feet of that change occurred
between 1995 and 2005. If warming continues, boreal tree species will run out of mountain and
become locally extinct. If they do, the animals that depend on these tree species will also
disappear from the mountain. One such species is Bicknell’s thrush, which breeds in the red
spruce forest at high elevations in New England; 25% of its breeding range is within a mile of
the A.T. If climate change causes the boreal forest to convert to northern hardwood forest,
Bicknell’s thrush may become extinct.
Further south, in the warmer Blue Ridge of Virginia, red spruce is found only at the highest
elevations. Here, too, it is migrating upslope, but since it covers less of the mountains than in
New England, it is more at risk of disappearing due to warming.
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Migration may not be a viable alternative for changes in precipitation. Prolonged drought could
cause plants or animals that need moist conditions to become extinct, at least locally. The one
recent species extinction clearly linked to climate change involved a Costa Rican tree frog that
became extinct after a prolonged drought dried up all of its breeding areas.
In addition to concerns about protecting the A.T.’s existing fauna and flora, climate change and
rising CO2 concentrations, in combination with other global changes (e.g. increased nitrogen
deposition and habitat disruption) could increase exotic invasive plant and animal infestations.
The characteristics (quick growth and dispersion, lack of natural enemies, and ability to adapt to
a wide range of conditions) that cause exotic invasives to be problems, could give these species
an additional advantage as climate change upsets existing ecosystems. These concerns are well
understood in qualitative terms, but the complexity of the interactions involved, and uncertainty
about the details of future climate creates, makes it impossible to predict the future behavior of
specific exotic invasives.
Changes Due to More Extreme Climate
Changes in climate extremes, the highest or lowest temperatures during a month, drought, or
severe storms, would significantly impact the A.T. The impacts include:
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Warmer winter temperatures would increase the hiking season. However, many plant pests
are kept at low levels because they are killed off by cold winter temperatures. Warmer winter
temperatures would mean that insects such as pine borers are more likely to survive.
•
Higher summer temperatures would make summer hiking on the A.T. less enjoyable.
•
Drought, as a result of higher temperatures and less precipitation, would become more likely.
This discussion has already mentioned one impact of drought: the disappearance of the water
sources hikers depend on. Drought would also weaken or kill trees. Trees weakened by
drought are more susceptible to insect attack. Finally, drought can affect the Trail directly, by
making its treadway more susceptible to erosion.
•
Ice storms can cause millions of blow-downs, some of which would block the trail. Warmer
temperatures mean that the region susceptible to ice storms will move northward. Climate
models cannot tell us whether there will be more ice storms, but they do indicate that the
region they affect will change.
•
Hurricane-force winds are unusual along the A.T., but the Trail is susceptible to erosion from
the heavy rains that accompany these storms. Hurricanes draw their energy from the warm
water of the ocean surface, and there has long been concern that as the oceans warm
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hurricanes will become more common and/or more intense. Climate model projections do not
project an increase in the numbers of hurricanes, but they do project an increase in the
intensity of the hurricanes that do form. More intense hurricanes could mean more erosion of
the A.T. and increased blow-downs.
•
Warmer, drier conditions could increase the number of forest fires. Also of concern is the
potential increase in fuel for these fires. The die-off of trees as a result of the change from
boreal to northern hardwood forests, and increased blow-downs as a result of either ice
storms or increase hurricane strength, could result in more intense, more destructive forest
fires.
To summarize: The climate changes projected for the next 50 years would have significant
impacts on the A.T. They would change the A.T. hiking experience and create new challenges to
ATC’s on-going efforts to maintain and protect the Trail.
Topic 8 - How is ATC Responding to the Threat Climate Change Poses to the A.T.?
ATC has long recognized that climate change poses a threat to the A.T. In 2008, ATC’s Board of
Directors passed a resolution committing the organization to a number of actions:
1. Reducing its own carbon dioxide emissions
The largest source of carbon dioxide emission resulting from ATC activities is the carbon
dioxide emitted by the vehicles ATC members and other A.T. visitors use to get to the Trail for
hiking, maintenance and other activities. ATC member Clubs have long promoted car-pooling to
save money and reduce these emissions. More recently, ATC Staff has promoted car-pooling to
Board of Directors and Stewardship Council meetings, and used conference calls instead of
meetings to reduce travel requirements. Reducing vehicle use for ATC activities is an on-going
effort at both the member club and ATC levels.
ATC owns and operates several buildings and is working to improve their energy efficiency.
This is a challenging task because the buildings are old and were constructed long before energy
efficiency and carbon dioxide emissions were important considerations. An energy efficiency
audit of ATC’s Headquarters building in Harpers Ferry, West Virginia, a historic building built
in 1892, identified a number of action items that could be taken to reduce building energy use
while increasing comfort levels in the building. Some of these items have already been
completed, including:
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a. digital, programmable thermostats have been installed limiting heating and cooling of
the building to periods when the building is actually in use;
b. all incandescent light bulbs have been replaced with CFLs;
c. large air leaks around doors and windows have been sealed to prevent loss of warm
air in the winter and cool air in the summer; and
d. the building attic has been prepared for additional insulation, which will be installed
in the near future.
Other items will be addressed as funding is available.
ATC operates Bears Den Hostel outside Bluemont, Virginia, in a stone building built in 1933.
Recently, the building’s original single pane glass windows have been replaced with modern,
low-E glass windows. The building was heated by two, low efficiency furnaces that burned
heating oil. One of the furnaces has been replaced with a high efficiency propane furnace, and
plans have been made to replace the other. The energy efficiency improvements already made
have reduced Bears Den’s fuel usage by about a third. Additionally, since propane is a lower
carbon fuel than heating oil, an thus produces less CO2 per unit of heat, a further reduction in
carbon dioxide emissions has been achieved. Completion of the renovations at Bears Den has
greatly reduced emissions, as well as reducing ATC’s fuel costs.
Finally, ATC owns and operates the Kellogg Education Center in near Great Barrington,
Massachusetts. The building was originally a farmhouse built in 1744. An environmental survey
has been conducted on the building. A list of actions to reduce greenhouse gas emissions and
other environmental impacts is now available. These will be implemented as funds and volunteer
time become available.
2. Educate ATC members and Trail visitors on climate change and its wide-ranging effects on
the Appalachian National Scenic Trail.
This website is the major tool being used to meet this commitment. In addition, articles on
climate change have appeared in AT Journeys, and workshops on climate change will be part of
every ATC Biennial meeting.
3. Educate ATC members and Trail visitors about the availability of mass transit and other lowcarbon transportation alternatives for accessing trailheads.
The ATC website has information about public transportation to the A.T. and shuttle services
that will transport hikers from public transportation to the trail. To access this information visit
www.appalachiantrail.org/transportation.
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4. Monitor climate change indicators and collect climate-relevant data through the MEGATransect and other environmental monitoring programs.
As discussed in Topic 7, changes in habitat will be the most obvious impact of climate change on
the A.T. Change can only be measured against a baseline, that is, the current habitat along the
A.T. Comprehensive measurements of the current state of A.T. habitats are underway. Much of it
is carried out using remote sensing techniques, aerial photography and satellite imagery. Aerial
photographs of the southern third of the A.T. will be obtained in Fall, 2009, and actual mapping
of the trail habitats will start in 2010.
Special consideration is given to rare plant species. These cannot be identified remotely, a
qualified botanist must walk the Trail and identify them. Between 1989 and 2000, almost a
dozen major inventories were contracted by ATC and the National Park Service with state
natural heritage offices and qualified biologists. These contractors identified 1759 occurrences of
rare plants and animals along the A.T.
ATC and the National Park Service subsequently developed a new procedure that improves the
identification, inventory of condition, and reporting on these plants. A “train-the-trainer” session
was held in March 2009 for regional coordinators for this program. They will now train the
dozens of volunteers who hike to the inventoried communities of plants, monitor and report on
these rare and threatened species.
The National Park Service (NPS) is developing an Appalachian Trail Environmental Monitoring
Plan to coordinate the various monitoring efforts now underway. NPS expects to have this plan
ready mid-2010. ATC volunteers are expected to play an important role in implementing this
plan.
5. Include climate change considerations in ATC advocacy efforts.
The resolution contains four commitments related to advocacy:
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Promote mass transit accessibility to trailheads;
Support appropriate state and federal carbon-reducing policies and measures;
Urge continuing efforts to protect Appalachian forest lands for the increasingly important
purpose of carbon sequestration and climate moderation; and
Recognize the value of A.T. lands as a corridor to allow wildlife to adapt to climate
change, and take this into account in future actions.
These commitments are now part of the ATC’s on-going advocacy effort.
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During the June, 2009, House of Representatives debate on the proposed American Clean
Energy and Security Act (HR 2454, also known as the Waxman-Markey Bill), ATC wrote to
Speaker of the House Pelosi supporting the goals and specific features of the bill that had
specific ties to the A.T. (http://www.appalachiantrail.org/atf/cf/%7BB8A229E6-1CDC-41B7A615-2D5911950E45%7D/Speaker_Pelosi_ltr.%206-19-09.pdf)
6. Conduct further research and analysis with the Appalachian Trail Park Office to determine if
the Appalachian National Scenic Trial can meet the criteria for inclusion in the National
Park Service’s “Climate Friendly Parks” program in concert with the implementation of
these efforts.
This effort is abeyance until sufficient positive results can be obtained from ATC’s other climate
change-related activities.
7. Partner with other like-minded organizations in carbon reducing efforts and climate change
educations programs.
ATC has a long history of partnerships with the Federal and State agencies that own and manage
the land the A.T. passes through. ATC will be an active partner with these agencies as they
develop plans to address climate change.
ATC also partners with other non-profit organizations including the National Parks Conservation
Association, the National Wildlife Federation, The Nature Conservancy, Southern
Environmental Law Center, and a host of others.
Topic 9 – More Information
Climate and Climate Change Science (Topics 1-5)
Full reports from the UN’s Intergovernmental Panel on Climate Change (www.ipcc.ch) are long
and detailed. They are written by experts for experts. However, they are also summarized in a
more readable fashion in Summaries for Policymakers. The Summary for Policymakers from the
Synthesis Report of the IPCC’s Fourth Assessment Report, published in 2007, is a relatively
short, readable summary of what is known about climate change, its impacts, and the options for
addressing the threat. (www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf)
The Union of Concerned Scientists has published a summary of the IPCC Fourth Assessment
Report which may be easier to read than the IPCC’s summary. It can be found at
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www.ucsusa.org/global-warming/science-and-impacts/scienmce/findings-of-the-ipcc-fourth3.html.
Numerous other organizations have also published summaries of climate and climate change
science. If you have a favorite, please let us know and we will add it to this page.
Does Everyone Agree (Topic 6)
Source Watch has posted a useful summary of the common claims made by climate change
skeptics and their rebuttal. It can be found at
www.sourcewatch.org/index.php?title=climate_change_skeptics/common_claims_and_rebuttal
Impacts of Climate Change on the A.T. (Topic 7)
For more detail on the Climate Wizard projections of climate change along the A.T., see
www.climatewizard.org/AT_5_mile_Buffer.
For more information about the potential impacts of climate change on the U.S. see the recent
EPA report Climate Change Impacts in the United States,
www.globalchange.gov/publications/reports/scientific-assessments/us-impacts.
For more detail on the impacts of climate change on the forests of New England, see Confronting
Climate Change in the U.S. Northeast: Science, Impacts and Solutions
www.climatechoices.org/assets/documents/climatechoices/confronting-climate-change-in-the-us-northeast.pdf
For more detail about Bicknell’s Thrush and other threatened and endangered species along the
A.T. see a report titled Appalachian Trail Vital Signs.
www.appalachiantrail.org/atf/cf/%7BD25B4747-42A3-8D48EF35C0B0D9F1%7D/APPA_report_VsSummary_NETN_01302006.pdf
Since this web address is extremely complicated, the report can also be accessed by Googleing
“Appalachian Trail Vital Signs.”
What ATC Is Doing (Topic 8)
The ATC website has information about public transportation to the A.T. and shuttle services
that will transport hikers from public transportation to the trail. To access this information visit
www.appalachiantrail.org/transportation.
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Appendix I – Projecting Future Climate
Scientists have two general methods for projecting future conditions, statistical analysis and
modeling. Statistical approaches work on the assumption that the past predicts the future. For
example, if we know that a baseball player has a .333 batting average, we can predict that he’ll
get ten hits in his next thirty at bats. This may not happen. He may go into a slump and only get
five hits, or he may get hot and get fifteen hits, but ten hits is the best prediction we can make.
Some observers have tried to use simple statistical reasoning to predict future climate.
Unfortunately, the climate system is far too complex for this simple approach. This leaves
modeling as the only practical method.
A scientific model is a set of mathematical equations that describe a complex system. Some
scientific models are highly accurate. For example, we can send space probes to the moons of
Saturn because we have a highly accurate model of the gravitational interactions in the solar
system.
Climate Models
Climate models use the equations to describe the physical processes occurring in the climate
system. These include the heating of the atmosphere and Earth surface by the Sun’s radiation,
evaporation of water from both land and the oceans, formation of clouds from water vapor,
condensation of water vapor to form rain and snow, movement of air due to wind, loss of wind
energy due to friction over land, and a large number of other phenomena.
Because it is impossible to get an exact solution to the large set of equations that make up a
climate model, numerical techniques are used. The Earth’s surface is divided into a number of
squares, and the oceans and atmosphere are divided into layers, creating a large number of boxes.
The equations that make up the climate model are solved for one box and the results are used as
input for the adjacent boxes. The process is continued until the equations have been solved for all
boxes and calculated conditions for adjacent boxes are in close agreement. Then conditions are
readjusted for a short period of time later, typically an hour or less, and the process repeated until
climate has been calculated for whatever period of time the climate modelers are interested in.
Figure A-1 shows a schematic of a climate model.
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Figure A-1: Schematic for a Climate Model
Source: NOAA, http://celebrating200years.noaa.gov/brakthroughs/cliamte_model/welcome.html
Scientific models, including climate models, are only as good as their equations and the physical
values which are used as inputs to those equations. To go back to the space probe example, we
know their equations are very good, but if a mistake is made in the physical values used as input
to these equations, as happened in the case of one Mars Lander, the model’s calculations will be
wrong and the mission will be a failure.
Models of the climate system are not as accurate as those used for space probes for two reasons.
First, climate modelers are not in agreement about the equations they should use to characterize
the climate system. One way of characterizing the effect of the choices that climate modelers
make is to compare the model’s climate sensitivity. Climate sensitivity is defined at the model’s
estimate of equilibrium global average temperature increase that would result from doubling
atmospheric concentration of CO2 but making no other changes in the climate system. This is an
artificial case; many factors in the climate system are constantly changing, so the system is never
at equilibrium. However, since it is an easily defined case, it is one that has been evaluated on a
wide variety of climate models. After comparing results from a wide range of climate models,
the UN’s Intergovernmental Panel on Climate Change (IPCC) concluded that climate sensitivity
was between 2 and 4.5oC (3.6 – 8.1oF), with a best estimate of 3oC (5.4oF).
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Second, we cannot accurately estimate future greenhouse gas emissions, a critical input for
climate models. Greenhouse gas emissions depend on the future path of human development.
How many people will there be? How wealthy will they be? How much energy will they use and
what will be the sources of that energy? Because the answers to these questions are unknowable
for even twenty years into the future, climate scientists use a scenario approach.
Emission Scenarios
A scenario is a plausible picture of the future, not a forecast. If we think the world is going to act
quickly and effectively to control greenhouse gas emissions, then our scenario would have low
greenhouse gas emissions, as well as low emissions of the other pollutants associated with fossil
fuel use. If we think that the world is going to continue to ignore the threat of climate change,
our scenario would have high greenhouse gas emissions. If we think the answer is someplace in
the middle, our scenario would have an intermediate level of greenhouse gas emissions.
The most commonly used emission scenarios for climate modeling are the six SRES (Special
Report on Emission Scenarios) marker scenarios published by the IPCC (Intergovernmental
Panel on Climate Change) in 2000. While these scenarios assume that no action is taken to
control greenhouse gas emissions, other factors, such as the degree of air pollution control, result
in wide variations in projected emissions of CO2. Since CO2 has a long lifetime in the
atmosphere, more than 1000 years, atmospheric concentrations of CO2 depend on cumulative
emissions of CO2 over a long period of time. The SRES scenarios can be ranked by their
cumulative CO2 emissions from 1990 to 2100.
Many critics have questioned the plausibility of the SRES scenarios, since some of them project
seemly incredible rates of economic growth in the poorest parts of the world. Also, the
assumption that the world will take no action to control greenhouse gas emissions for the next
100 years is clearly wrong, since action is already being taken by many countries, and many
others will take action long before 2100. However, if rather than focusing on the details of the
scenarios, they are considered to define a reasonable range for future global greenhouse gas
emissions, they become useful tools for climate modeling.
Results from Global Climate Models
Global climate models provide reasonable consistency in their projections of global and
continental average temperatures. Figure A-2 shows the calculations of future global average
temperatures by 17 different global climate models using the same emission scenario.
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Figure A-2
Future Global Average Temperature Change as Calculated by 17 Different
Climate Models Using the Same Emission Scenario as Input
Source: IPCC (2007), Fourth Assessment Report, Working Group I, Figure 10.5.
However, climate models are less consistent in their projection of precipitation, particularly over
smaller areas. Figure A-3 shows the number of global models predicting increases in
precipitation over North America during the summer at the end of the 21st century.
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Figure A-3
Agreement among 21 Global Climate Models on Increases in Precipitation
Changes during the Summer over North America Between the End of the 20th
Century and the End of the 21st Century
Source: IPCC (2007), Fourth Assessment Report, Working Group I, Figure 11.12.
The darker areas in the figure indicate a high level of agreement between the global models,
while the lighter or browner areas indicate a low level of agreement. All, or almost all, global
models project that there will be more precipitation in the high Arctic, and most agree that there
will be less precipitation in the Caribbean and Central America. However, over much of the U.S.
and central Mexico, the global models are split, with roughly half projecting more precipitation
and the rest projecting less.
Global climate models do not agree on projections for smaller areas because they use different
equations to characterize the climate system and because of limited computer capacity. As shown
in Figure A-1, global climate models divide the Earth’s atmosphere and oceans into a very large
number of boxes. The climate model’s equations have to be solved for each of those boxes. To
keep the calculation requirements reasonable, climate model boxes are typically more than 100
miles on a side. Within a box, all conditions are averaged. Even with this simplification, it takes
the best supercomputers several months of computing time to do a full simulation of the Earth’s
climate over the next 100 years.
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Techniques for Projecting Climate Change Over Small Areas
The large size of climate model boxes and averaging within the box is not a serious problem in
flat areas where surface and climate conditions do not change rapidly. However, it is a problem
for mountainous areas, such as those traversed by the A.T., because in the mountains climate
changes dramatically over short distances. For example, North Carolina’s wettest city, Brevard,
is only 45 miles and several mountain ridges away from its driest city, Asheville.
To deal with the problem of rapidly changing conditions, climate modelers use a technique
known as downscaling. They take several boxes from a large climate model and divide them into
smaller boxes. They then use the average conditions found by the large climate model as initial
conditions and solve the model for each of the smaller boxes in the downscaled model. The
downscaled model can much more accurately represent mountain and other terrain features that
affect climate. The smaller the boxes in the downscaled model, the more detail can be included,
but the more computer time is required to solve the model.
Climate Wizard
The Nature Conservancy (TNC) in cooperation with the University of Washington and the
University of Southern Mississippi has developed a tool they call Climate Wizard
(www.climatewizard.org), which can downscale to boxes as small as five miles on a side (25
square miles). The system can make projections of future temperature and precipitation using
three different climate models and three different emission scenarios. It can also provide
ensemble results by averaging results from the three models for each of the emission scenarios.
In total, Climate Wizard can provide 12 different projections of future temperature and
precipitation.
The three climate models and their climate sensitivities are:
Model
CSIRO-MK3.0
UKMO-HadCM3
MIROC3.2 (medres)
Climate Sensitivity, oC
3.1
3.3
4.0
Source: IPCC (2007), Fourth Assessment Report, Working Group I, Table 8.2, Pg. 631.
While the models all have climates sensitivities in the range estimated by IPCC, all three are
above IPCC’s 3oC best estimate for climate sensitivity. This means that their estimates of climate
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change will tend to be some somewhat higher than models which use the best estimate of climate
sensitivity.
The three emission scenarios and their cumulative CO2 emissions 1990-2100 are:
Scenario
A2 (High)
A1B (Medium)
B1 (Low)
Cumulative CO2 Emissions, 1990-2100
Billion Metric Tonnes*
6800
5500
3600
1 metric tonne = 2205 pounds, or 1.1025 U.S. ton
Source: IPCC (2000), Special Report on Emission Scenarios, Table SPM-3b.
Note: IPCC results have been converted from metric tonnes of carbon to metric tonnes of carbon
dioxide.
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Appendix II – Climate Wizard Results
Historical Average Climate
Figure B-1 A.T. Annual Average Temperature (1951-2006)
Data source: Climate Wizard, Map by Matt Robinson, ATC
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Figure B-2 A.T, Annual Average (1951-2006) Precipitation
Data source: Climate Wizard, Map by Matt Robinson, ATC
20
Figure B-3 A.T. Summer Average Temperature (1951-2006)
Data source: Climate Wizard, Map by Matt Robinson, ATC
21
Figure B-4 A.T. Summer Average Precipitation (1951-2006)
Data source: Climate Wizard, Map by Matt Robinson, ATC
22
Figure B-5 A.T. Winter Average Temperature (1951-2006)
Data source: Climate Wizard, Map by Matt Robinson, ATC
23
Figure B-6 A.T. Winter Average Precipitation (1951-2006)
Data source: Climate Wizard, Map by Matt Robinson, ATC
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Moderate Climate Change Case – Model CSIRO-MK3.0, Emission Scenario SRES A1B
Figure B-7 – Projected Average Annual Temperature Increase in 2041-2060 – Moderate Climate
Change Case
25
Figure B-8 – Projected Average Annual Precipitation Change in 2041-2060 – Moderate Climate
Change Case
26
Figure B-9 – Projected Average Summer Temperature Increase in 2041-2060 – Moderate
Climate Change Case
27
Figure B-10 – Projected Average Summer Precipitation Change in 2041-2060 – Moderate
Climate Change Case
28
Figure B-11 – Projected Average Winter Temperature Increase in 2041-2060 – Moderate
Climate Change Case
29
Figure B-12 – Projected Average Winter Precipitation Change in 2041-2060 – Moderate Climate
Change Case
30
More Extreme Climate Change Case – Model MIROC 3.2, Emission Scenario SRES A2
Figure B-13 – Projected Average Annual Temperature Increase in 2041-2060 – More Extreme
Climate Change Case
31
Figure B-14 – Projected Average Annual Precipitation Change in 2041-2060 – More Extreme
Climate Change Case
32
Figure B-15 – Projected Average Summer Temperature Increase in 2041-2060 – More Extreme
Climate Change Case
33
Figure B-16 – Projected Average Summer Precipitation Change Increase in 2041-2060 – More
Extreme Climate Change Case
34
Figure B-17 – Projected Average Winter Temperature Increase in 2041-2060 – More Extreme
Climate Change Case
35
Figure B-18 – Projected Average Winter Precipitation Change Increase in 2041-2060 – More
Extreme Climate Change Case
36