Expert answer:RISK OF EXTREME WEATHER EVENTS
Expert answer:Question:Select one of the five ‘reasons for concern’ form the
reading and discuss why you chose that specific topic and its importance in
recent debates on climate change issues. Your discussion should demonstrate
your solid understanding of climate change and its interaction with humans. You
Will need to use both the assigned reading and external sources(s) to support
your thesis.please Make sure to Write an essay of 500 words on ONE of the below
topics. Include a Works Cited or References list, using accurate MLA or
APA documentation style.
assessing_dangerous_climate_change_through_an_update_of_the_ipcc.pdf
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SEE COMMENTARY
Assessing dangerous climate change through an
update of the Intergovernmental Panel on Climate
Change (IPCC) ‘‘reasons for concern’’
Joel B. Smitha,1, Stephen H. Schneiderb,c,1, Michael Oppenheimerd, Gary W. Yohee, William Haref,
Michael D. Mastrandreac, Anand Patwardhang, Ian Burtonh, Jan Corfee-Morloti, Chris H. D. Magadzaj,
Hans-Martin Füsself, A. Barrie Pittockk, Atiq Rahmanl, Avelino Suarezm, and Jean-Pascal van Yperselen
aStratus Consulting, Inc., Boulder, CO 80306-4059; bDepartment of Biology and cWoods Institute for the Environment, Stanford University, Stanford,
CA 94305; dDepartment of Geosciences and the Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, NJ 08544;
eDepartment of Economics, Wesleyan University, Middletown, CT 06459; fPotsdam Institute for Climate Impact Research, 14473 Potsdam, Germany;
gShailesh J. Mehta School of Management, Indian Institute of Technology-Bombay Powai, Mumbai 400076, India; hUniversity of Toronto, Toronto,
ON M6J 2C1 Canada; iOrganisation for Economic Cooperation and Development, 75776 Paris Cedex 16, France; jDepartment of Biological Sciences,
University Lake Kariba Research Station, Harare, Zimbabwe; kCSIRO Marine and Atmospheric Research, Aspendale 3195, Australia; lBangladesh Centre
for Advanced Studies, Dhaka, 1212 Bangladesh; mInstitute of Ecology and Systematic, Cuba Environmental Agency, 10800 Havana, Cuba; and nInstitut
d’Astronomie et de Géophysique Georges Lemaı̂tre, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
Contributed by Stephen H. Schneider, December 9, 2008 (sent for review March 18, 2008)
Article 2 兩 UNFCCC 兩 climate change impacts
A
rticle 2 of the United Nations Framework Convention on
Climate Change (UNFCCC) commits signatory nations to
stabilizing greenhouse gas concentrations in the atmosphere at
a level that ‘‘would prevent dangerous anthropogenic interference (DAI) with the climate system.’’ The UNFCCC also
highlights 3 broad metrics with which decision-makers are to
assess the pace of progress toward this goal: allow ‘‘ecosystems
to adapt naturally to climate change,’’ ensure that ‘‘food production is not threatened,’’ and enable ‘‘economic development
to proceed in a sustainable manner.’’ In an effort to provide
some insight into impacts that might be considered DAI, authors
of the Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) identified 5 ‘‘reasons for
concern’’ (RFCs) in (1). Each RFC categorizes impacts of a
similar type, providing a set of metrics reflecting severity of risk.
Relationships between various impacts reflected in each RFC
and increases in global mean temperature (GMT) were por-
www.pnas.org兾cgi兾doi兾10.1073兾pnas.0812355106
trayed in what has come to be called the ‘‘burning embers
diagram’’; the image was also included in the Summary for Policy
Makers of the contribution of Working Group II to the TAR and
highlighted in the Synthesis Report.
In presenting the ‘‘embers’’ in the TAR, IPCC authors did not
assess whether any single RFC was more important than any
other; nor, as they noted, did they conclude what level of impact
or what atmospheric concentrations of greenhouse gases would
constitute DAI, a value judgment that would be policyprescriptive. The ‘‘embers’’ were designed primarily to communicate the associations of impacts with increases in GMT and
facilitate examination of the underlying evidence for use by
decision-makers contemplating responses to these concerns.
The IPCC Fourth Assessment Report (AR4) states that ‘‘the
‘reasons for concern’ identified in the TAR remain a viable
framework for assessing key vulnerabilities’’ (2). In this article,
we revise sensitivities of the RFCs to increases in GMT, based
on our expert judgment about new findings in the growing
literature since the publication of the TAR in 2001.* Furthermore, our judgments are supported by a more thorough understanding of the concept of vulnerability that has evolved over the
past 8 years,† as well as a more careful articulation of the criteria
by which any specific vulnerability can be labeled ‘‘key,’’ and thus
contribute to a reason for concern (3).‡
Section 1 defines and reviews the RFCs and ‘‘burning embers’’
figure as presented in the IPCC TAR. Section 2 presents the
Author contributions: J.B.S., S.H.S., M.O., G.W.Y., W.H., M.D.M., A.P., I.B., J.C.-M., C.H.D.M.,
H.-M.F., A.B.P., A.R., A.S., and J.-P.v.Y. performed research; and J.B.S., S.H.S., M.O., G.W.Y.,
W.H., M.D.M., A.P., I.B., J.C.-M., C.H.D.M., H.-M.F., A.B.P., A.R., A.S., and J.-P.v.Y. wrote the
paper.
Conflict of interest statement: The authors declare no conflict of interest.
Freely available online through the PNAS open access option.
See Commentary on page 4065.
1To
whom correspondence may be addressed. E-mail: jsmith@stratusconsulting.com or
shs@stanford.edu.
*These judgments were vetted by 3 rounds of IPCC review and were approved in the
Summary for Policymakers of both the AR4 Working Group 2 and Synthesis Reports by the
IPCC Plenary.
†Vulnerability
to climate change is the degree to which geophysical, biological and socioeconomic systems are susceptible to and unable to cope with adverse impacts of climate change.
‡The
criteria are: (i) magnitude of impacts; (ii) timing of impacts; (iii) persistence and
reversibility of impacts; (iv) potential for adaptation; (v) distributional aspects of impacts
and vulnerabilities; (vi) likelihood (estimates of uncertainty) of impacts and vulnerabilities
and confidence in those estimates; and (vii) importance of the system(s) at risk. IPCC
authors applied only the first 6 criteria in its assessment, because ‘‘importance’’ is really a
subjective judgment by a potential decision-maker and thus crosses too far into the realm
of being ‘‘policy prescriptive’’; we follow the same convention.
PNAS 兩 March 17, 2009 兩 vol. 106 兩 no. 11 兩 4133– 4137
ENVIRONMENTAL
SCIENCES
Article 2 of the United Nations Framework Convention on Climate
Change [United Nations (1992) http://unfccc.int/resource/docs/
convkp/conveng.pdf. Accessed February 9, 2009] commits signatory nations to stabilizing greenhouse gas concentrations in the
atmosphere at a level that ‘‘would prevent dangerous anthropogenic interference (DAI) with the climate system.’’ In an effort to
provide some insight into impacts of climate change that might be
considered DAI, authors of the Third Assessment Report (TAR) of
the Intergovernmental Panel on Climate Change (IPCC) identified 5
‘‘reasons for concern’’ (RFCs). Relationships between various impacts reflected in each RFC and increases in global mean temperature (GMT) were portrayed in what has come to be called the
‘‘burning embers diagram.’’ In presenting the ‘‘embers’’ in the TAR,
IPCC authors did not assess whether any single RFC was more
important than any other; nor did they conclude what level of
impacts or what atmospheric concentrations of greenhouse gases
would constitute DAI, a value judgment that would be policy
prescriptive. Here, we describe revisions of the sensitivities of the
RFCs to increases in GMT and a more thorough understanding of
the concept of vulnerability that has evolved over the past 8 years.
This is based on our expert judgment about new findings in the
growing literature since the publication of the TAR in 2001,
including literature that was assessed in the IPCC Fourth Assessment Report (AR4), as well as additional research published since
AR4. Compared with results reported in the TAR, smaller increases
in GMT are now estimated to lead to significant or substantial
consequences in the framework of the 5 ‘‘reasons for concern.’’
TAR (2001) Reasons For Concern
Updated Reasons For Concern
5
Large
Increase
Negative
for Most
Regions
Net
Negative
in All
Metrics
Higher
5
Risks to
Many
Large
Increase
Negative
for Most
Regions
Net
Negative
in All
Metrics
High
4
4
3
3
Future
2
Risks to
Some
Increase
Negative
for Some
Regions;
Positive
for
Others
Positive or
Negative
Market
Impacts;
Majority
of People
Adversely
Affected
2
1
Very
Low
0
Risks to
Some
Increase
Negative
for Some
Regions;
Positive
for
Others
Positive or
Negative
Market
Impacts;
Majority
of People
Adversely
Affected
1
Increase in Global Mean Temperature above circa 1990 (°C)
Risks to
Many
Low
0
Past
Risks to
Unique
and
Threatened
Systems
Risk of
Extreme
Weather
Events
Distribution
of Impacts
Aggregate
Impacts
-0.6
Risks of Large
Scale
Discontinuities
Risks to
Unique
and
Threatened
Systems
Risk of
Extreme
Weather
Events
Distribution
of Impacts
Aggregate
Impacts
-0.6
Risks of Large
Scale
Discontinuities
Fig. 1. Risks from climate change, by reason for concern—2001 compared with updated data. Climate change consequences are plotted against increases in
global mean temperature (°C) after 1990. Each column corresponds to a specific RFC and represents additional outcomes associated with increasing global mean
temperature. The color scheme represents progressively increasing levels of risk and should not be interpreted as representing ‘‘dangerous anthropogenic
interference,’’ which is a value judgment. The historical period 1900 to 2000 warmed by ⬇0.6 °C and led to some impacts. It should be noted that this figure
addresses only how risks change as global mean temperature increases, not how risks might change at different rates of warming. Furthermore, it does not
address when impacts might be realized, nor does it account for the effects of different development pathways on vulnerability. (A) RFCs from the IPCC TAR as
described in section 1. (B) Updated RFCs derived from IPCC AR4 as supported by the discussion in section 2. (Reproduced with permission from Climate Change
2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate
Change. Figure SPM-2. Cambridge University Press.)
update of the RFCs and the ‘‘burning embers’’ figure derived
from the recently released IPCC AR4 and subsequent literature.
The final section compares the earlier representation with the
updated version.
exceed 5 °C by 2100. An increase in GMT ⬎5 °C by 2100 would
have even more adverse effects within each RFC than has been
analyzed.
The right side of Fig. 1 tracks the updated 5 RFCs against
increases in GMT above 1990.§
The IPCC TAR and Reasons for Concern. Fig. 1 Left replicates the
version of the ‘‘burning embers’’ diagram that was offered as
figure SPM-2 in the Summary for Policymakers of the contribution of Working Group II to the TAR (4). IPCC AR4
projected a range of 1.1 °C to 6.4 °C increase in GMT from 1990
to 2100 (5) based on 6 IPCC Special Report on Emissions
Scenarios (SRES) nonmitigation scenarios (6). Although uncertainty in the response of the climate system to increasing
greenhouse gas concentrations contributes to this very broad
spread in projections of increase in GMT, the magnitude of
future emissions driven by alternative development pathways
plays a comparable role. The assessed ‘‘likely range’’ (66–90%)
of global temperature increase by 2100 for the lowest emissions
scenario (SRES B1) is 1.1 °C to 2.9 °C, whereas the likely range
for the highest scenario (SRES A1FI) is 2.4 °C to 6.4 °C. Since
2000, the trajectory of global emissions is above the highest
SRES scenario (5). The observed temperature change, reflecting the response to date of the climate system to historical
emissions, is also at the top of the projected range of temperature
increase (7). The temperature increases in Fig. 1 go up to 5 °C
although, as the IPCC projects, the increase in GMT could
Risk to Unique and Threatened Systems. This RFC addresses the
4134 兩 www.pnas.org兾cgi兾doi兾10.1073兾pnas.0812355106
potential for increased damage to or irreversible loss of unique
and threatened systems, such as coral reefs, tropical glaciers,
endangered species, unique ecosystems, biodiversity hotspots,
small island states, and indigenous communities.
Risk of Extreme Weather Events. This RFC tracks increases in
extreme events with substantial consequences for societies and
natural systems. Examples include increase in the frequency,
intensity, or consequences of heat waves, floods, droughts,
wildfires, or tropical cyclones.
Distribution of Impacts. This RFC concerns disparities of impacts.
Some regions, countries, and populations face greater harm
from climate change, whereas other regions, countries, or pop§It
is recognized that vulnerability can also be partly a function of the expected rate of
climate change, but this assessment focuses on the magnitude of change. These magnitudes are, however, projected to occur over time frames that imply rates of change that
are very likely to exceed the abilities of natural and human systems to adapt completely.
Smith et al.
Aggregate Damages. This RFC covers comprehensive measures
of impacts. Impacts distributed across the globe can be aggregated into a single metric, such as monetary damages, lives
affected, or lives lost. Aggregation techniques vary in their
treatment of equity of outcomes, as well as treatment of impacts
that are not easily quantified. This RFC is based mainly on
monetary aggregation available in the literature.
Risks of Large-Scale Discontinuities. This RFC represents the likelihood that certain phenomena (sometimes called singularities or
tipping points) would occur, any of which may be accompanied
by very large impacts. These phenomena include the deglaciation
(partial or complete) of the West Antarctic or Greenland ice
sheets and major changes in some components of the Earth’s
climate system, such as a substantial reduction or collapse of the
North Atlantic Meridional Overturning Circulation (8).
The RFCs were selected based on literature and judgments of
the authors about risks from climate change. As indicated in the
caption to Fig. 1, the authors made judgments for each RFC
about what increases in GMT above 1990 would be associated
with neutral or low impacts or risks (Fig. 1, white regions),
negative impacts for some systems or more significant risks (Fig.
1, yellow regions), and substantial negative impacts or risks that
are more widespread and/or severe (Fig. 1, red regions). In every
case, the number of impacts and the harm implied depended on
the rate of climate change, the amount of climate change, and the
vulnerability of the affected systems. However, no single metric
could adequately describe the diversity of impacts and associated
risks for any one RFC, let alone aggregate across all of them into
a single ‘‘dangerous’’ global temperature threshold. Within each
RFC, therefore, multiple metrics were aggregated through expert judgment, and no aggregation was attempted across the
RFCs. Moreover, it was clear that an objective ranking of relative
importance across the RFCs would be impossible.
The various shadings and the judgments they depict only took
autonomous adaptation into account (i.e., adaptation that might
be expected to occur in the absence of anticipatory policies and
measures), to the extent that such responses were captured by the
underlying literature. The impacts literature, however, often
makes simplifying assumptions about adaptation which can
result in overestimates or underestimates of the magnitude of
negative or beneficial impacts. Furthermore, there is little
information on the effects of proactive adaptation (i.e., adaptations implemented to anticipate and lessen the adverse impacts
of climate change, such as breeding new crop varieties or
planning for coastal protection) in reducing vulnerability. Thus,
it is uncertain how the relationship between the RFCs and
increase in GMT would be affected by consideration of proactive
adaptation.
In summary, the first 2 RFCs—Risks to Unique and Threatened Systems and Risks to Extreme Events—were judged in the
TAR to imply substantial impacts or risks (transition from yellow
to red) between 1 °C and 2 °C above 1990 levels. The third and
fourth RFCs—Distribution of Impact and Aggregate Impacts—
reflected substantial risks beginning in the range between 2 °C
and 3 °C. The fifth RFC—Risks of Large-Scale Discontinuities—was not judged to be a source of substantial risk until GMT
climbed more than 4 °C or 5 °C above the 1990 mean.
Updating the Reasons for Concern After the IPCC AR4. Fig. 1 Right
shows the results of our assessment based on literature since the
TAR. In updating the ‘‘embers,’’ we retained the same color
scheme and structure as the TAR. The same scale for temperature change frames the update. Transitions between colors
Smith et al.
SEE COMMENTARY
remain fuzzy because there was (and there still is) uncertainty
about the increase in GMT associated with a transition from
little or no risk to some risk and from some to substantial and/or
widespread risk for any specific system or sector. As was true in
the TAR, the aggregation of risk across many different sectors,
regions, or populations under a particular RFC is subjective, and
thereby introduces another source of uncertainty. The width and
placement of the transitions in each bar can nonetheless still be
interpreted as visual representations of aggregated damage
functions for each RFC, with narrower and lower transitions
representing rapidly changing levels of risk as a function of
temperature.
We take each RFC in turn in this update. Our assessment of
risk for each is based on not only new information about impacts
and vulnerabilities assessed in the AR4 and since, but also more
clearly established criteria for identifying ‘‘key vulnerabilities’’ (3).
Risks to Unique and Threatened Systems. There is new and stronger
evidence since the TAR of observed impacts of climate change
on unique and threatened systems (such as polar and high
mountain communities and ecosystems), with increasing levels
of adverse impacts as temperatures increase further. An increasing risk of species extinction and coral reef damage is projected
with higher confidence than in the TAR. There is medium
confidence that ⬇20–30% of known plant and animal species are
likely to be at increased risk of extinction if increases in global
average temperature exceed 1.5 °C to 2.5 °C over 1980–1999
levels (‘‘1990 levels’’ hereafter), a finding not made in the TAR
(9). Confidence has increased that a 1 °C to 2 °C increase in
GMT above 1990 levels poses significant risks to many unique
and threatened systems, including many biodiversity hotspots.
Corals are vulnerable to thermal stress and may have limited
adaptive capacity. Increases in sea surface temperature of ⬇1 °C
to 3 °C are projected to result in more frequent coral bleaching
events and widespread mortality unless there is substantial
thermal adaptation or acclimatization by corals (10, 11). Increasing vulnerability of Arctic indigenous communities and
small island communities to warming has been observed and is
projected to accelerate (12). Kurz et al. (13) found that outbreaks
of mountain pine beetle in British Columbia linked to climate
change have resulted in net loss of forest biomass.
On the basis of this evidence, particularly the emergence of a
number of adverse impacts that are clearly linked to anthropogenic climate change, the yellow shading in the leftmost bar of
Fig. 1 Right begins the transition to red slightly above 0 °C,
indicating substantial impacts and/or moderate risks at current
temperature levels. The darker red shading, indicating potentially severe and/or widespread impacts and associated increases
in risks, begins to appear ⬇1 °C.
Risks of Extreme Weather Events. It is now more likel …
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