The WA must include information (properly cited) from at least one of the assigned discussion readings and must contain information from at least two other references (i.e., a total of at least three references, all properly cited as described below). The course text and web sites can be used in addition to, but not instead of, your two additional references. You must also submit an outline of your paper that includes: title, thesis statement, main concepts to be discussed, and at least two supporting references (cited as described below). The outline should be submitted via Canvas about one week before the WA is due (see class schedule). You are encouraged to discuss assigned readings, but every student must submit an individual essay. The assignment must be written in your own words. Late writing assignments will NOT be accepted.This policy will be strictly enforced. Your paper should be well-written (spell-checked, logically-structured, coherent, concise, and include proper citations), critical, and imaginative. The format should include an introduction to the topic (including a rationale for why you are writing about the topic, and a thesis statement, wherein you state the point of view you will evaluate (either support or reject). The main body of the paper should contain facts (data) and some assessment of those data (e.g., not enough data, contradictory data, invalid assumptions) and how the problem you are discussing is related to the global environment. Finally, summarize with an evaluation of how the data you discussed led you to support or reject your thesis. After submitting your first draft, you will receive a grade and comments. Use this feedback to revise and improve your final draft, due two weeks after the first draft (see class schedule). The first and final drafts are worth an equal amount of points – so please do not submit a sloppy first draft or an unrevised final draft. Your final draft grade will NOT replace your first draft grade. You must turn in your graded first draft along with your final draft. Your final draft must be revised and improved based on the suggestions and comments you receive on your first draft. If you submit a final draft that is not revised, or if your revisions do not address any of the comments on your first draft, you will receive a 0. Your essay should make some progress toward explaining questions such as, (i) Why should anyone in the Central Valley care about El Nino (or desertification or thawing of permafrost)? or (ii) What assumptions were made in developing models of nitrogen cycling (or eutrophication, or greenhouse gas influence on climate change)?, or (iii) How good are the data used to test the hypothesis that global warming is occurring (or animal habitat is lost with desertification, or agricultural nitrogen fertilization leads to anoxia in marine systems)? Direct quotes must be enclosed in quotation marks and have an authordate citation. References must be properly cited i ...

1. The WA must include information (properly cited) from at least
one of the assigned discussion readings and must contain
information from at least two other references (i.e., a total of at
least three references, all properly cited as described below).
The course text and web sites can be used in addition to, but not
instead of, your two additional references. You must also
submit an outline of your paper that includes: title, thesis
statement, main concepts to be discussed, and at least two
supporting references (cited as described below). The outline
should be submitted via Canvas about one week before the WA
is due (see class schedule). You are encouraged to discuss
assigned readings, but every student must submit an individual
essay. The assignment must be written in your own words. Late
writing assignments will NOT be accepted.This policy will be
strictly enforced.
Your paper should be well-written (spell-checked, logically-
structured, coherent, concise, and include proper citations),
critical, and imaginative. The format should include an
introduction to the topic (including a rationale for why you are
writing about the topic, and a thesis statement, wherein you
state the point of view you will evaluate (either support or
reject). The main body of the paper should contain facts (data)
and some assessment of those data (e.g., not enough data,
contradictory data, invalid assumptions) and how the problem
you are discussing is related to the global environment. Finally,
summarize with an evaluation of how the data you discussed led
you to support or reject your thesis.
After submitting your first draft, you will receive a grade and
comments. Use this feedback to revise and improve your final
draft, due two weeks after the first draft (see class schedule).
The first and final drafts are worth an equal amount of points –
so please do not submit a sloppy first draft or an unrevised final

2. draft. Your final draft grade will NOT replace your first draft
grade. You must turn in your graded first draft along with your
final draft. Your final draft must be revised and improved based
on the suggestions and comments you receive on your first
draft. If you submit a final draft that is not revised, or if your
revisions do not address any of the comments on your first
draft, you will receive a 0.
Your essay should make some progress toward explaining
questions such as, (i) Why should anyone in the Central Valley
care about El Nino (or desertification or thawing of
permafrost)? or (ii) What assumptions were made in developing
models of nitrogen cycling (or eutrophication, or greenhouse
gas influence on climate change)?, or (iii) How good are the
data used to test the hypothesis that global warming is occurring
(or animal habitat is lost with desertification, or agricultural
nitrogen fertilization leads to anoxia in marine systems)?
Direct quotes must be enclosed in quotation marks and have an
authordate citation.
References must be properly cited in your paper. For our
purposes, in the text, the following style is required:
Backsoon and Seeyah (1998) showed that water flows uphill.
More recent work has shown that you can lead a horse to water
and you can make it drink (Backsoon, 2001). Finally, it remains
unclear if it is the heat or the humidity (Backsoon et al., 2005),
but whatever the cause, cosmic forces may be at play in
determining the fate of the globe (The Onion, 2008).
In the "References" section at the end of the paper, the
following style of citation is required:
Journal articles:
Backsoon, I.L.B, and Seeyah, B.I. 1998. El Nino or El

3. Nonsense? Journal of Cosmetology 1:115119.
Books:
Backsoon, I.L.B. 2001. The facts behind clichés. 2nd ed.
Bemidji State University Press, Bemidji, MN.
Newspaper or magazine articles:
Backsoon, I.L.B., Verisi, X.O., and Enopi, L.M. 2005. Heat or
humidity? Duluth Daily Diatribe. 2 January, p. A2.
Web Sources:
The Onion. 2008. Scientists warn large earth collider may
destroy earth.
http://www.theonion.com/content/news/scientists_warn_large_e
arth. (Date viewed: 18 December 2008).
1
Irreversible climate change due to carbon
dioxide emissions
Susan Solomona,1, Gian-Kasper Plattnerb, Reto Knuttic, and
Pierre Friedlingsteind
aChemical Sciences Division, Earth System Research
Laboratory, National Oceanic and Atmospheric Administration,
Boulder, CO 80305; bInstitute of
Biogeochemistry and Pollutant Dynamics and cInstitute for
Atmospheric and Climate Science, ETH CH-8092, Zurich,
Switzerland; and dInstitut Pierre Simon
Laplace/Laboratoire des Sciences du Climat et de
l’Environnement, Unité Mixte de Recherche 1572 Commissariat

4. à l’Energie Atomique–Centre National de la
Recherche Scientifique–Université Versailles Saint-Quentin,
Commissariat a l’Energie Atomique-Saclay, l’Orme des
Merisiers, 91191 Gif sur Yvette, France
Contributed by Susan Solomon, December 16, 2008 (sent for
review November 12, 2008)
The severity of damaging human-induced climate change
depends
not only on the magnitude of the change but also on the
potential
for irreversibility. This paper shows that the climate change that
takes place due to increases in carbon dioxide concentration is
largely irreversible for 1,000 years after emissions stop.
Following
cessation of emissions, removal of atmospheric carbon dioxide
decreases radiative forcing, but is largely compensated by
slower
loss of heat to the ocean, so that atmospheric temperatures do
not
drop significantly for at least 1,000 years. Among illustrative
irreversible impacts that should be expected if atmospheric
carbon
dioxide concentrations increase from current levels near 385
parts
per million by volume (ppmv) to a peak of 450 – 600 ppmv over
the
coming century are irreversible dry-season rainfall reductions in
several regions comparable to those of the ‘‘dust bowl’’ era and
inexorable sea level rise. Thermal expansion of the warming
ocean
provides a conservative lower limit to irreversible global
average
sea level rise of at least 0.4 –1.0 m if 21st century CO2
concentra-

5. tions exceed 600 ppmv and 0.6 –1.9 m for peak CO2
concentrations
exceeding �1,000 ppmv. Additional contributions from glaciers
and ice sheet contributions to future sea level rise are uncertain
but
may equal or exceed several meters over the next millennium or
longer.
dangerous interference � precipitation � sea level rise �
warming
Over the 20th century, the atmospheric concentrations of
keygreenhouse gases increased due to human activities. The
stated objective (Article 2) of the United Nations Framework
Convention on Climate Change (UNFCCC) is to achieve stabi-
lization of greenhouse gas concentrations in the atmosphere at
a low enough level to prevent ‘‘dangerous anthropogenic inter-
ference with the climate system.’’ Many studies have focused
on
projections of possible 21st century dangers (1–3). However,
the
principles (Article 3) of the UNFCCC specifically emphasize
‘‘threats of serious or irreversible damage,’’ underscoring the
importance of the longer term. While some irreversible climate
changes such as ice sheet collapse are possible but highly
uncertain (1, 4), others can now be identified with greater
confidence, and examples among the latter are presented in this
paper. It is not generally appreciated that the atmospheric
temperature increases caused by rising carbon dioxide concen-
trations are not expected to decrease significantly even if
carbon
emissions were to completely cease (5–7) (see Fig. 1). Future
carbon dioxide emissions in the 21st century will hence lead to
adverse climate changes on both short and long time scales that
would be essentially irreversible (where irreversible is defined
here as a time scale exceeding the end of the millennium in year

6. 3000; note that we do not consider geo-engineering measures
that might be able to remove gases already in the atmosphere or
to introduce active cooling to counteract warming). For the
same
reason, the physical climate changes that are due to anthropo-
genic carbon dioxide already in the atmosphere today are
expected to be largely irreversible. Such climate changes will
lead
to a range of damaging impacts in different regions and sectors,
some of which occur promptly in association with warming,
while
others build up under sustained warming because of the time
lags
of the processes involved. Here we illustrate 2 such aspects of
the
irreversibly altered world that should be expected. These
aspects
are among reasons for concern but are not comprehensive; other
possible climate impacts include Arctic sea ice retreat, increases
in heavy rainfall and f looding, permafrost melt, loss of glaciers
and snowpack with attendant changes in water supply, increased
intensity of hurricanes, etc. A complete climate impacts review
is presented elsewhere (8) and is beyond the scope of this paper.
We focus on illustrative adverse and irreversible climate
impacts
for which 3 criteria are met: (i) observed changes are already
occurring and there is evidence for anthropogenic contributions
to these changes, (ii) the phenomenon is based upon physical
principles thought to be well understood, and (iii) projections
are
available and are broadly robust across models.
Advances in modeling have led not only to improvements in
complex Atmosphere –Ocean General Circulation Models
(AOGCMs) for projecting 21st century climate, but also to the

7. implementation of Earth System Models of Intermediate Com-
plexity (EMICs) for millennial time scales. These 2 types of
models are used in this paper to show how different peak carbon
dioxide concentrations that could be attained in the 21st century
are expected to lead to substantial and irreversible decreases in
dry-season rainfall in a number of already-dry subtropical areas
and lower limits to eventual sea level rise of the order of
meters,
implying unavoidable inundation of many small islands and
low-lying coastal areas.
Results
Longevity of an Atmospheric CO2 Perturbation. As has long
been
known, the removal of carbon dioxide from the atmosphere
involves multiple processes including rapid exchange with the
land biosphere and the surface layer of the ocean through air–
sea
exchange and much slower penetration to the ocean interior that
is dependent upon the buffering effect of ocean chemistry along
with vertical transport (9 –12). On the time scale of a
millennium
addressed here, the CO2 equilibrates largely between the atmo-
sphere and the ocean and, depending on associated increases in
acidity and in ocean warming (i.e., an increase in the Revelle or
‘‘buffer’’ factor, see below), typically �20% of the added
tonnes
of CO2 remain in the atmosphere while �80% are mixed into
the
ocean. Carbon isotope studies provide important observational
constraints on these processes and time constants. On multimil-
lenium and longer time scales, geochemical and geological
Author contributions: S.S., G.-K.P., R.K., and P.F. designed
research; S.S., G.-K.P., and R.K.
performed research; G.-K.P. and R.K. analyzed data; and S.S.,

8. G.-K.P., R.K., and P.F. wrote
the paper.
The authors declare no conflict of interest.
Freely available online through the PNAS open access option.
1To whom correspondence should be addressed. E-mail:
[email protected]
This article contains supporting information online at
www.pnas.org/cgi/content/full/
0812721106/DCSupplemental.
© 2009 by The National Academy of Sciences of the USA
1704 –1709 � PNAS � February 10, 2009 � vol. 106 � no. 6
www.pnas.org�cgi�doi�10.1073�pnas.0812721106
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tal
http://www.pnas.org/cgi/content/full/0812721106/DCSupplemen
tal
processes could restore atmospheric carbon dioxide to its pre-
industrial values (10, 11), but are not included here.
Fig. 1 illustrates how the concentrations of carbon dioxide
would be expected to fall off through the coming millennium if
manmade emissions were to cease immediately following an
illustrative future rate of emission increase of 2% per year
[comparable to observations over the past decade (ref. 13)] up
to peak concentrations of 450, 550, 650, 750, 850, or 1,200
ppmv;
similar results were obtained across a range of EMICs that were

9. assessed in the Intergovernmental Panel on Climate Change
(IPCC) Fourth Assessment Report (5, 7). This is not intended to
be a realistic scenario but rather to represent a test case whose
purpose is to probe physical climate system changes. A more
gradual reduction of carbon dioxide emission (as is more
likely),
or a faster or slower adopted rate of emissions in the growth
period, would lead to long-term behavior qualitatively similar to
that illustrated in Fig. 1 (see also Fig. S1). The example of a
sudden cessation of emissions provides an upper bound to how
much reversibility is possible, if, for example, unexpectedly
damaging climate changes were to be observed.
Carbon dioxide is the only greenhouse gas whose falloff
displays multiple rather than single time constants (see Fig. S2).
Current emissions of major non-CO2 greenhouse gases such as
methane or nitrous oxide are significant for climate change in
the
next few decades or century, but these gases do not persist over
time in the same way as carbon dioxide (14).
Fig. 1 shows that a quasi-equilibrium amount of CO2 is
expected to be retained in the atmosphere by the end of the
millennium that is surprisingly large: typically �40% of the
peak
concentration enhancement over preindustrial values (�280
ppmv). This can be easily understood on the basis of the
observed instantaneous airborne fraction (AFpeak) of �50% of
anthropogenic carbon emissions retained during their buildup in
the atmosphere, together with well-established ocean chemistry
and physics that require �20% of the emitted carbon to remain
in the atmosphere on thousand-year timescales [quasi-
equilibrium airborne fraction (AFequi), determined largely by
the
Revelle factor governing the long-term partitioning of carbon
between the ocean and atmosphere/biosphere system] (9 –11).

10. Assuming given cumulative emissions, EMI, the peak concen-
tration, CO2peak (increase over the preindustrial value CO20),
and the resulting 1,000-year quasi-equilibrium concentration,
CO2equi can be expressed as
CO2
peak � CO2
0 � AFpeak�EMI [1]
CO2
equi � CO2
0 � AFequi�EMI [2]
so that
CO2
equi � CO2
0 �
AFequi
AFpeak
� CO2
peak � CO2
0� . [3]
Given an instantaneous airborne fraction (AFpeak) of �50%
during the period of rising CO2, and a quasi-equilbrium
airborne
factor (AFequi) of 20%, it follows that the quasi-equilibrium
enhancement of CO2 concentration above its preindustrial value
is �40% of the peak enhancement. For example, if the CO2
concentration were to peak at 800 ppmv followed by zero

11. emissions, the quasi-equilibrium CO2 concentration would still
be far above the preindustrial value at �500 ppmv. Additional
carbon cycle feedbacks could reduce the efficiency of the ocean
and biosphere to remove the anthropogenic CO2 and thereby
increase these CO2 values (15, 16). Further, a longer decay time
and increased CO2 concentrations at year 1000 are expected for
large total carbon emissions (17).
Irreversible Climate Change: Atmospheric Warming. Global
average
temperatures increase while CO2 is increasing and then remain
approximately constant (within � �0.5 °C) until the end of the
millennium despite zero further emissions in all of the test cases
shown in Fig. 1. This important result is due to a near balance
between the long-term decrease of radiative forcing due to CO2
concentration decay and reduced cooling through heat loss to
the oceans. It arises because long-term carbon dioxide removal
1800 2000 2200 2400 2600 2800 3000
400
600
800
1000
1200
C
O
2
(p
pm

12. v)
1800 2000 2200 2400 2600 2800 3000
0
1
2
3
4
5
S
ur
fa
ce
W
ar
m
in
g
(K
)
1800 2000 2200 2400 2600 2800 3000
0

13. 0.5
1
1.5
2
T
he
rm
al
e
xp
an
si
on
(
m
)
Emission
growth
Zero emission after peaks
Peak
at 1200
850
750

14. 650
550
450
Global average
warming
Thermal expansion
of ocean
Year
2%/year growth
to peak
preindustrial
Fig. 1. Carbon dioxide and global mean climate system changes
(relative to
preindustrial conditions in 1765) from 1 illustrative model, the
Bern 2.5CC
EMIC, whose results are comparable to the suite of assessed
EMICs (5, 7).
Climate system responses are shown for a ramp of CO2
emissions at a rate of
2%/year to peak CO2 values of 450, 550, 650, 750, 850, and
1200 ppmv,
followed by zero emissions. The rate of global fossil fuel CO2
emission grew at
�1%/year from 1980 to 2000 and �3%/year in the period from
2000 to 2005
(13). Results have been smoothed using an 11-year running
mean. The 31-year
variation seen in the carbon dioxide time series is introduced by
the climatol-

15. ogy used to force the terrestrial biosphere model (15). (Top)
Falloff of CO2
concentrations following zero emissions after the peak.
(Middle) Globally
averaged surface warming (degrees Celsius) for these cases
(note that this
model has an equilibrium climate sensitivity of 3.2 °C for
carbon dioxide
doubling). Warming over land is expected to be larger than
these global
averaged values, with the greatest warming expected in the
Arctic (5). (Bot-
tom) Sea level rise (meters) from thermal expansion only (not
including loss of
glaciers, ice caps, or ice sheets).
Solomon et al. PNAS � February 10, 2009 � vol. 106 � no. 6
� 1705
EN
V
IR
O
N
M
EN
TA
L
SC
IE
N

16. C
ES
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plemental_PDF#nameddest=SF2
and ocean heat uptake are both dependent on the same physics
of
deep-ocean mixing. Sea level rise due to thermal expansion ac-
companies mixing of heat into the ocean long after carbon
dioxide
emissions have stopped. For larger carbon dioxide
concentrations,
warming and thermal sea level rise show greater increases and
display transient changes that can be very rapid (i.e., the rapid
changes in Fig. 1 Middle), mainly because of changes in ocean
circulation (18). Paleoclimatic evidence suggests that additional
contributions from melting of glaciers and ice sheets may be
comparable to or greater than thermal expansion (discussed
further
below), but these are not included in Fig. 1.
Fig. 2 explores how close the modeled temperature changes
are to thermal equilibrium with respect to the changing carbon
dioxide concentration over time, sometimes called the realized
warming fraction (19) (shown for the different peak CO2 cases).
Fig. 2 Left shows how the calculated warmings compare to
those
expected if temperatures were in equilibrium with the carbon
dioxide concentrations vs. time, while Fig. 2 Right shows the
ratio
of these calculated time-dependent and equilibrium tempera-

17. tures. During the period when carbon dioxide is increasing, the
realized global warming fraction is �50 – 60% of the
equilibrium
warming, close to values obtained in other models (5, 19). After
emissions cease, the temperature change approaches equilib-
rium with respect to the slowly decreasing carbon dioxide
concentrations (cyan lines in Fig. 2 Right). The continuing
warming through year 3000 is maintained at �40 – 60% of the
equilibrium warming corresponding to the peak CO2 concen-
tration (magenta lines in Fig. 2 Right). Related changes in
fast-responding atmospheric climate variables such as precipi-
tation, water vapor, heat waves, cloudiness, etc., are expected to
occur largely simultaneously with the temperature changes.
Irreversible Climate Change: Precipitation Changes. Warming is
expected to be linked to changes in rainfall (20), which can
adversely affect the supply of water for humans, agriculture,
and
ecosystems. Precipitation is highly variable but long-term
rainfall
decreases have been observed in some large regions including,
e.g., the Mediterranean, southern Africa, and parts of south-
western North America (21–25). Confident projection of future
changes remains elusive over many parts of the globe and at
small
scales. However, well-known physics (the Clausius–Clapeyron
law) implies that increased temperature causes increased atmo-
spheric water vapor concentrations, and changes in water vapor
transport and the hydrologic cycle can hence be expected
(26 –28). Further, advances in modeling show that a robust
characteristic of anthropogenic climate change is poleward
expansion of the Hadley cell and shifting of the pattern of
precipitation minus evaporation (P–E) and the storm tracks (22,
26), and hence a pattern of drying over much of the already-dry
subtropics in a warmer world (�15°-40° latitude in each hemi-
sphere) (5, 26). Attribution studies suggest that such a drying

18. pattern is already occurring in a manner consistent with models
including anthropogenic forcing (23), particularly in the south-
western United States (22) and Mediterranean basin (24, 25).
We use a suite of 22 available AOGCM projections based
upon the evaluation in the IPCC 2007 report (5, 29) to charac-
terize precipitation changes. Changes in precipitation are ex-
pected (5, 20, 30) to scale approximately linearly with
increasing
warming (see Fig. S3). The equilibrium relationship between
precipitation and temperature may be slightly smaller (by
�15%) than the transient values, due to changes in the land/
ocean thermal contrast (31). On the other hand, the observed
20th century changes follow a similar latitudinal pattern but
presently exceed those calculated by AOGCMs (23). Models
that
include more complex representations of the land surface, soil,
and vegetation interactively are likely to display additional
feedbacks so that larger precipitation responses are possible.
Here we evaluate the relationship between temperature and
precipitation averaged for each month and over a decade at each
grid point. One ensemble member is used for each model so that
all AOGCMs are equally weighted in the multimodel ensemble;
results are nearly identical if all available model ensemble
members are used.
Fig. 3 presents a map of the expected dry-season (3 driest
consecutive months at each grid point) precipitation trends per
degree of global warming. Fig. 3 shows that large uncertainties
remain in the projections for many regions (white areas). How-
ever, it also shows that there are some subtropical locations on
every inhabited continent where dry seasons are expected to
become drier in the decadal average by up to 10% per degree of
warming. Some of these grid points occur in desert regions that

19. are already very dry, but many occur in currently more
temperate
and semiarid locations. We find that model results are more
robust over land across the available models over wider areas
for
drying of the dry season than for the annual mean or wet season
(see Fig. S4). The Insets in Fig. 3 show the monthly mean
projected precipitation changes averaged over several large
regions as delineated on the map. Increased drying of respective
dry seasons is projected by �90% of the models averaged over
the indicated regions of southern Europe, northern Africa,
southern Africa, and southwestern North America and by �80%
of the models for eastern South America and western Australia
(see Fig. S3). Although given particular years would show
exceptions, the long-term irreversible warming and mean
rainfall
changes as suggested by Figs. 1 and 3 would have important
consequences in many regions. While some relief can be ex-
pected in the wet season for some regions (Fig. S4), changes in
dry-season precipitation in northern Africa, southern Europe,
and western Australia are expected to be near 20% for 2 °C
warming, and those of southwestern North America, eastern
South America, and southern Africa would be �10% for 2 °C of
global mean warming. For comparison, the American ‘‘dust
Fig. 2. Comparison between calculated time-dependent surface
warming in the Bern2.5CC model and the values that would be
expected if temperatures were
in equilibrium with respect to the CO2 enhancements,
illustrative of 2%/year emission increases to 450, 550, 650, 750,
850, and 1,200 ppmv as in Fig. 1. (Left) The
actual and equilibrium temperature changes (based upon the
model’s climate sensitivity at equilibrium). The cyan lines in
Right show the ratio of actual and
equilibrium temperatures (or realized fraction of the warming
for the time-dependent CO2 concentrations), while the magenta

20. lines show the ratio of actual
warming to the equilibrium temperature for the peak CO2
concentration.
1706 � www.pnas.org�cgi�doi�10.1073�pnas.0812721106
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plemental_PDF#nameddest=SF3
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plemental_PDF#nameddest=SF4
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bowl’’ was associated with averaged rainfall decreases of �10%
over �10 –20 years, similar to major droughts in Europe and
western Australia in the 1940s and 1950s (22, 32). The spatial
changes in precipitation as shown in Fig. 3 imply greater
challenges in the distribution of food and water supplies than
those with which the world has had difficulty coping in the past.
Such changes occurring not just for a few decades but over
centuries are expected to have a range of impacts that differ by
region. These include, e.g., human water supplies (25), effects
on
dry-season wheat and maize agriculture in certain regions of
rain-fed farming such as Africa (33, 34), increased fire fre-
quency, ecosystem change, and desertification (24, 35–38).
Fig. 4 Upper relates the expected irreversible changes in
regional dry-season precipitation shown in Fig. 3 to best esti-
mates of the corresponding peak and long-term CO2 concen-
trations. We use 3 °C as the best estimate of climate sensitivity
across the suite of AOGCMs for a doubling of carbon dioxide

21. from preindustrial values (5) along with the regional drying
values depicted in Fig. 3 and assuming that �40% of the carbon
dioxide peak concentration is retained after 1000 years. Fig. 4
shows that if carbon dioxide were to peak at levels of �450
ppmv,
irreversible decreases of �8 –10% in dry-season precipitation
would be expected on average over each of the indicated large
regions of southern Europe, western Australia, and northern
Africa, while a carbon dioxide peak value near 600 ppmv would
be expected to lead to sustained rainfall decreases of �13–16%
in the dry seasons in these areas; smaller but statistically
significant irreversible changes would also be expected for
southwestern North America, eastern South America, and
Southern Africa.
Irreversible Climate Change: Sea Level Rise. Anthropogenic
carbon
dioxide will cause irrevocable sea level rise. There are 2
relatively
well-understood processes that contribute to this and a third that
may be much more important but is also very uncertain. Warm-
ing causes the ocean to expand and sea levels to rise as shown
in
Fig. 1; this has been the dominant source of sea level rise in the
past decade at least (39). Loss of land ice also makes important
contributions to sea level rise as the world warms. Mountain
glaciers in many locations are observed to be retreating due to
warming, and this contribution to sea level rise is also relatively
well understood. Warming may also lead to large losses of the
Greenland and/or Antarctic ice sheets. Additional rapid ice
losses from particular parts of the ice sheets of Greenland and
Antarctica have recently been observed (40 – 42). One recent
study
uses current ice discharge data to suggest ice sheet
contributions of

22. up to 1–2 m to sea level rise by 2100 (42), but other studies
suggest
that changes in winds rather than warming may account for
currently observed rapid ice sheet f low (43), rendering
quantitative
extrapolation into the future uncertain. In addition to rapid ice f
low,
slow ice sheet mass balance processes are another mechanism
for
potential large sea level rise. Paleoclimatic data demonstrate
large
contributions of ice sheet loss to sea level rise (1, 4) but
provide
limited constraints on the rate of such processes. Some recent
studies suggest that ice sheet surface mass balance loss for peak
CO2
concentrations of 400 – 800 ppmv may be even slower than the
removal of manmade carbon dioxide following cessation of
emis-
Fig. 3. Expected decadally averaged changes in the global
distribution of precipitation per degree of warming (percentage
of change in precipitation per
degree of warming, relative to 1900 –1950 as the baseline
period) in the dry season at each grid point, based upon a suite
of 22 AOGCMs for a midrange future
scenario (A1B, see ref. 5). White is used where fewer than 16 of
22 models agree on the sign of the change. Data are monthly
averaged over several broad regions
in Inset plots. Red lines show the best estimate (median) of the
changes in these regions, while the red shading indicates the
�1-� likely range (i.e., 2 of 3 chances)
across the models.
Solomon et al. PNAS � February 10, 2009 � vol. 106 � no. 6
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sions, so that this loss could contribute less than a meter to
irreversible sea level rise even after many thousands of years
(44,
45). It is evident that the contribution from the ice sheets could
be
large in the future, but the dependence upon carbon dioxide
levels
is extremely uncertain not only over the coming century but
also in
the millennial time scale.
An assessed range of models suggests that the eventual

24. contribution to sea level rise from thermal expansion of the
ocean is expected to be 0.2– 0.6 m per degree of global warming
(5). Fig. 4 uses this range together with a best estimate for
climate
sensitivity of 3 °C (5) to estimate lower limits to eventual sea
level
rise due to thermal expansion alone. Fig. 4 shows that even with
zero emissions after reaching a peak concentration, irreversible
global average sea level rise of at least 0.4 –1.0 m is expected if
21st century CO2 concentrations exceed 600 ppmv and as much
as 1.9 m for a peak CO2 concentration exceeding �1,000 ppmv.
Loss of glaciers and small ice caps is relatively well understood
and is expected to be largely complete under sustained warming
of, for example, 4 °C within �500 years (46). For lower values
of
warming, partial remnants of glaciers might be retained, but this
has not been examined in detail for realistic representations of
glacier shrinkage and is not quantified here. Complete losses of
glaciers and small ice caps have the potential to raise future sea
level by �0.2– 0.7 m (46, 47) in addition to thermal expansion.
Further contributions due to partial loss of the great ice sheets
of Antarctica and/or Greenland could add several meters or
more to these values but for what warming levels and on what
time scales are still poorly characterized.
Sea level rise can be expected to affect many coastal regions
(48). While sea walls and other adaptation measures might
combat some of this sea level rise, Fig. 4 shows that carbon
dioxide peak concentrations that could be reached in the future
for the conservative lower limit defined by thermal expansion
alone can be expected to be associated with substantial irrevers-
ible commitments to future changes in the geography of the
Earth because many coastal and island features would ultimately
become submerged.

25. Discussion: Some Policy Implications
It is sometimes imagined that slow processes such as climate
changes pose small risks, on the basis of the assumption that a
choice can always be made to quickly reduce emissions and
Fig. 4. Illustrative irreversible climate changes as a function of
peak carbon dioxide reached. (Upper) Best estimate of expected
irreversible dry-season
precipitation changes for the regions shown in Fig. 3, as a
function of the peak carbon dioxide concentration during the
21st century. The quasi-equilibrium CO2
concentrations shown correspond to 40% remaining in the long
term as discussed in the text. The precipitation change per
degree is derived for each region
as in Fig. 3; see also Fig. S3. The yellow box indicates the
range of precipitation change observed during typical major
regional droughts such as the ‘‘dust bowl’’
in North America (32). (Lower) Corresponding irreversible
global warming (black line). Also shown is the associated lower
limit of irreversible sea level rise
(because of thermal expansion only based upon a range of 0.2–
0.6 m/°C), from an assessment across available models (5).
Smaller values (by �30%) for expected
warming, precipitation, and thermal sea level rise would be
obtained if climate sensitivity is smaller than the best estimate
while larger values (by �50%) would
be expected for the upper end of the estimated likely range of
climate sensitivity (49).
1708 � www.pnas.org�cgi�doi�10.1073�pnas.0812721106
Solomon et al.
http://www.pnas.org/cgi/data/0812721106/DCSupplemental/Sup
plemental_PDF#nameddest=SF3

26. thereby reverse any harm within a few years or decades. We
have
shown that this assumption is incorrect for carbon dioxide
emissions, because of the longevity of the atmospheric CO2
perturbation and ocean warming. Irreversible climate changes
due to carbon dioxide emissions have already taken place, and
future carbon dioxide emissions would imply further
irreversible
effects on the planet, with attendant long legacies for choices
made by contemporary society. Discount rates used in some
estimates of economic trade-offs assume that more efficient
climate mitigation can occur in a future richer world, but
neglect
the irreversibility shown here. Similarly, understanding of irre-
versibility reveals limitations in trading of greenhouse gases on
the basis of 100-year estimated climate changes (global
warming
potentials, GWPs), because this metric neglects carbon
dioxide’s
unique long-term effects. In this paper we have quantified how
societal decisions regarding carbon dioxide concentrations that
have already occurred or could occur in the coming century
imply irreversible dangers relating to climate change for some
illustrative populations and regions. These and other dangers
pose substantial challenges to humanity and nature, with a
magnitude that is directly linked to the peak level of carbon
dioxide reached.
Materials and Methods
The AOGCM simulation data presented in this paper are part of
the World
Climate Research Program’s (WCRP’s) Coupled Model
Intercomparison Project
phase 3 (CMIP3) multimodel data set (29) and are available
from the Program for

27. Climate Model Diagnosis and Intercomparison (PCMDI) (www-
pcmdi.llnl.
gov/ipcc/about�ipcc.php), where further information on the
AOGCMs can also be
obtained. The EMIC used in this study is the Bern2.5CC EMIC
described in refs. 7
and 15; it is compared to other models in refs. 5 and 7. It is a
coupled climate–
carbon cycle model of intermediate complexity that consists of
a zonally averaged
dynamic ocean model, a 1-layer atmospheric energy–moisture
balance model,
and interactive representations of the marine and terrestrial
carbon cycles.
ACKNOWLEDGMENTS. We gratefully acknowledge the
modeling groups, the
Program for Climate Model Diagnosis and Intercomparison, and
the World
Climate Research Program’s Working Group on Coupled
Modeling for their
roles in making available the Working Group on Coupled
Modeling’s Coupled
Model Intercomparison Project phase 3 multimodel data set.
Support of this
data set is provided by the Office of Science, U.S. Department
of Energy. We
also appreciate helpful comments from 3 reviewers.
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Sungjoong Kim
999372920
1/19/2017
Writing outline #1
Climate change
Thesis statement
Emission of carbon dioxide minimizes radiation forcing, slower
the heat loss towards an ocean, so due to this climatic change
temperature of the atmosphere will not drop until next 1000
years.
Introduction
From the 20th century the concentration of gases increased in
atmosphere due to more human actions. Further in the next
century, emission, of carbon dioxide increases to a larger extent
and this activity lead a frequent change in climate at both large
and short scale. According to Solomon et al. 2009 the change in
climate at any place is not only based on alteration in magnitude
but also on the irreversibility. The change in climate that occurs
because of increase in concentration of carbon dioxide is
irreversible for next 1000 years. The more carbon dioxide
emission removing it from the atmosphere, but on the other
hand reducing emission of heat and radiations towards ocean so
that can stabilize the temperature of atmosphere. Generally it is
not good to increase atmospheric temperature by full ceasing

36. and concentration of carbon dioxide. So emission of carbon
dioxide caused the stability in temperature of atmosphere.
Background
According to Gillet et al. 2011 the problem of irreversible
destruction should take actions to handle climate change.
According to international change in climate policy, the induced
carbon dioxide is termed to be irreversible change in climate at
both short and large scale. Make use of Canadian model of earth
system to determine that concentration and ceasing of more
carbon dioxide in the atmosphere causes increase in temperature
worldwide which is not good. Because when temperature
increases then it will show more warmth and less loss of
radiations towards ocean. That thing is not good in terms of
climatic change. According to Ricke and Caldeira, 2014 the
emission of carbon dioxide caused more warmth on earth. The
researchers found median time of 10.1 years among warming
effect and emission effect with probability up to 90 percent. The
emission of carbon dioxide can be avoided by this generation
and for sure this will be helpful for the future generation.
References
Gillett, N., Arora, V., Zickfeld, K., Marshall, S., and
Merryfield, W. (2011). Ongoing climate change following a
complete cessation of carbon dioxide emissions.
Ricke, K. and Caldeira, K. (2014). Maximum warming occurs
about one decade after a carbon dioxide emission.
Environmental research.
Solomon, S., Plattner, G., Knutti, R., and Friedlingstein, P.
(2009). Irreversible climate change due to carbon dioxide
emissions. Vol. 106.(Reference #1)
Feedback from TA : You will want to developed a narrow and
debatable thesis. It must also presents evidence that supports
your claim.

37. ESM 120 – Writing Workshop 1
Writing a Thesis Statement
What is a thesis statement?
A thesis is an arguable statement that can be supported with
evidence. It should include both the main
argument of the paper as well as the supporting arguments that
you will use to back this claim up. It should not
be vague or merely a summary of facts without analysis or
interpretation.
1) A thesis statement must be debatable:
Example of a non-debatable thesis statement:
Pollution is bad for the environment.
Example of a debatable thesis statement:
At least 25 percent of the federal budget should be spent on
limiting pollution.
Another example of a debatable thesis statement:
America's anti-pollution efforts should focus on privately
owned cars.
2) A thesis statement must be narrow:
Example of a thesis that is too broad:

38. The government should work to fight pollution.
Narrowed debatable thesis 1:
At least 25 percent of the federal budget should be spent on
helping upgrade business to clean technologies,
researching renewable energy sources, and planting more trees
in order to control or eliminate pollution.
Narrowed debatable thesis 2:
America's anti-pollution efforts should focus on privately
owned cars because it would allow most citizens to
contribute to national efforts and care about the outcome.
3) A thesis statement makes claims that will be supported later
in the paper:
Example of a thesis that doesn't make any claims:
Humans should relocate to Mars.
Thesis with claims to be supported:
It is too late to save earth; therefore, humans should
immediately set a date for their relocation to Mars where,
with proper planning, they can avoid issues of famine, war, and
global warming.
Our example (based on Solomon et al. 2009 paper): Climate

39. change poses a greater and longer-lived threat to
human life than previously considered because of irreversible
increases in global temperature, rise in sea level,
and changes in precipitation patterns caused by past
anthropogenic emissions.
What is good about this thesis statement? What could be
improved?
Take a look at the below thesis statements. Determine if they
are complete thesis statements and revise
them if necessary.
As developing countries become larger players in
industrialization and production, a substantial shift in
emissions regulations should be made to compensate for the
increasing rates of environmental degradation.
Farmers are implementing alternative methods to sustainable
food production to reduce the effects of climate
change.
Livestock production cannot be the solution for growing world
population and hunger. Livestock (solely for
products) negatively affects the environment in many ways.
Although the actions of humans have committed Earth’s climate
to an irreversible level of change,
geoengineering may be a plausible method of slowing or
reversing Earth’s unfavorable forecast.

40. Increasing global surface temperatures resulting from human
induced climate change is and will continue to
greatly affect the range and distribution of many major
terrestrial and marine animal species.
Time permitting: with a partner, brainstorm three thesis
statements based on the IPCC Summary to
Policymakers that we read last week.
Stuck on figuring out the type of thesis you want to write?
Check out four types of argumentative thesis
claims below:
Claims typically fall into one of four categories. Thinking about
how you want to approach your topic, in other
words what type of claim you want to make, is one way to focus
your thesis on one particular aspect of your
broader topic.
Claims of fact or definition: These claims argue about what the
definition of something is or whether
something is a settled fact. Example:

41. What some people refer to as global warming is actually nothing
more than normal, long-term cycles of climate
change.
Claims of cause and effect: These claims argue that one person,
thing, or event caused another thing or event
to occur. Example:
The popularity of SUV's in America has caused pollution to
increase.
Claims about value: These are claims made of what something
is worth, whether we value it or not, how we
would rate or categorize something. Example:
Global warming is the most pressing challenge facing the world
today.
Claims about solutions or policies: These are claims that argue
for or against a certain solution or policy
approach to a problem. Example:
Instead of drilling for oil in Alaska we should be focusing on
ways to reduce oil consumption, such as
researching renewable energy sources.
Sources:
The Writing Lab & The OWL at Purdue and Purdue University.
Kibin, Essay Writing: https://www.kibin.com/essay-writing-
blog/thesis-statement-examples/

42. Guidelines for Writing Assignments
You will complete two writing assignments in ESM 120. For
each writing assignment, you will craft an
argument and support that argument using scientific evidence.
Papers should be related to topics
covered in discussion. No late work will be accepted, so make
sure to turn your writing assignments
in on time.
Length/Format: 500 word limit (no more than 2 pages)
- Header should be one line
- 12 point font, 1 inch margins
⁃ Argument paper with (see rubric for more detailed
guidelines):
o An introduction that includes a thesis statement
o Body paragraphs that have topic sentences and support the
thesis with cited scientific
evidence
§ Make sure to interpret the evidence (explain how it fits into
your argument) as
well as evaluate the evidence (is this strong evidence? How was
it obtained? Are
there studies that have found contradictory results? Are all
assumptions valid?)
§ Your body paragraphs should synthesize multiple references
when appropriate.
Avoid writing body paragraphs that are merely a summary of a
single reference.

43. o A conclusion that wraps up your argument by assessing how
the data support your
thesis statement and connects your topic to the global
environment
Revisions:
⁃ You will submit two drafts of each paper: a first draft and a
final draft
⁃ After submitting your first draft, you will receive a grade and
comments. Use this feedback to
revise and improve your final draft, due two weeks after the
first draft.
⁃ The first draft and final draft are worth an equal amount of
points – so please do not submit a
sloppy first draft or an unrevised final draft.
⁃ You must turn in your first draft along with your final draft
when submitting your final draft for
grading.
⁃ You must revise and improve your final draft. If you submit a
final draft that is not revised, or if
your revisions do not address any of the comments on your first
draft, you will receive a 0.
References:
- You should use at least one of the assigned readings as a
reference
- You must have 2 additional primary references (e.g. scientific
journal articles) for a total of 3
primary references. Primary references should be the bulk of

44. your citations, News articles are
not primary references!
- You can use textbook and websites in addition to (not in place
of) the 3 primary references
- Web link in citations are only necessary when you are citing a
website (e.g. not necessary
when citing online newspaper articles)
- Use the online database, Web of Science, to find scientific
journal articles. See instructions
below on how to access Web of Science.
- You must have a reference section at the end of your paper.
Use the following style:
Journal articles:
Backsoon, I.L.B, and Seeyah, B.I. 1998. El Nino or El
Nonsense? Journal of Cosmetology
1:115-119.
Books:
Backsoon, I.L.B. 2001. The facts behind clichés. 2nd ed.
Bemidji State University Press,
Bemidji, MN.
Newspaper or magazine articles:
Backsoon, I.L.B., Verisi, X.O., and Enopi, L.M. 2005. Heat or
humidity? Duluth Daily Diatribe. 2

45. January, p. A2.
Web Sources:
The Onion. 2008. Scientists warn large earth collider may
destroy earth.
http://www.theonion.com/content/news/scientists_warn_large_e
arth. (Date viewed: 18
December 2008).
In-text citations:
- Must cite sources within the text in the proper format: e.g.
(Backsoon, 2001) or (Backsoon &
Seeyah, 1998)
o Note: one citation may be sufficient for several sentences if it
is clear that the sentences
are related
- Failure to cite information/data/thoughts that are not your own
within your paper is considered
plagiarism.
Writing style:
- Your paper must have a thesis statement. The purpose of the
paper is to make an argument
and evaluate evidence for and against that argument, not to be
descriptive.
- Use technical language. Your paper should follow a formal,
scientific style. It is possible to
write both eloquently and technically!

46. - Avoid fluffy prose, dramatic statements, and hyperbole.
- You must use facts, back them up and cite them. Failure to
cite information is considered
plagiarism.
- Do not use quotes; paraphrase information in your own words
- Make sure every paragraph has a topic and concluding
sentence
- Avoid use of ‘us’/’we’ such as ‘our country’ or ‘our earth’
(specify which country or the earth)
- Write concisely
Grammar:
- Put a noun after the word ‘this’ or don’t use the word ‘this’
- Don’t end a sentence with a preposition
- We recommend Strunk & White’s The Elements of Style as a
grammar/style guide
Science:
- Use scientific terms and define them when appropriate
- Use (cited) data to support your thesis; do not make
unsupported generalizations/claims
- Recognize uncertainty! Many environmental issues are not
black and white. Acknowledge
good arguments or evidence from the “other side” – and refute
them if possible.
Plagiarism
Scholarly work often involves reference to the ideas, data, and
conclusions of others’. Intellectual

47. honesty requires that such references be explicitly and clearly
cited. Plagiarism is an
EXTREMELY SERIOUS academic offence. If you have
questions regarding what is considered
plagiarism, please visit the following website for specific
examples.
• Resource on avoiding plagiarism:
https://owl.english.purdue.edu/owl/resource/589/01/
• Simple rule of thumb: if you have three or more words in a
row that are the same as the
writer’s phrasing, you need to place it in quotes and cite it.
Even better, reword the phrase (and
still cite it).
Writing Resources
If you need tutoring for writing skills, I recommend visiting the
Student Academic Success Center.
Writing and ESL specialists are available to meet one-on-one
with students to help with writing.
(http://success.ucdavis.edu/academic/writing.html).
Additional online writing resources:
http://twwc.ucdavis.edu/misc/online-writing-resources-to-
share-with-students/
Accessing Web of Science

48. Web of Science is a good way to find primary sources for
writing assignments. You can
search for topics that are relevant to your paper (e.g. El Nino
AND California
fisheries). Textbooks, news articles, and websites are not
acceptable primary sources for this
writing assignment, but can be used as additional references.
To access Web of Science from off campus, you must:
1) go to lib.ucdavis.edu
2) click VPN under Quick Links in the left hand column to log
in from off campus
2) click on Databases A-Z
3) search for 'Web of Science'
4) select the last item, 'Web of Science [via Web of
Knowledge]'