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The IPCC Assessment Process:
Future Projections of Climate
Change
Ronald J Stouffer
Geophysical Fluid Dynamics
Laboratory
NOAA
The views described here are solely
those of the presenter and not of
GFDL/NOAA/DOC or any other agency or
institution.
What is the IPCC?
http://www.ipcc.ch
• Established by:
• World Meteorological Organization (WMO)
• United Nations Environment Programme (UNEP)
• Open to all members of the UN and WMO
• Started in 1988 - Full reports in 1990, 1995, 2001, 2007
From the IPCC web pages:
“The role of the IPCC is to assess on a comprehensive,
objective, open and transparent basis the scientific,
technical and socio-economic information relevant to
understanding the scientific basis of risk of humaninduced climate change, its potential impacts and
options for adaptation and mitigation.”
What is the IPCC?
Every 5-6 years, over 1000 scientists from
more than 100 nations assess the published
scientific literature documenting the state of
scientific knowledge related to climate change
issues. The IPCC reports are ratified by the
~180 member nations.
NOAA GFDL has been a prime player in the 4
major assessment reports, including the IPCC
4th Assessment Report (AR4) published in
early 2007.
IPCC WGI 2007 Findings
• The planet is warming. The warming is not uniform. In fact, some
small areas are cooling. Other climate and biophysical changes support
the idea that the planet is warming. Sea ice and snow edges retreating;
increased precipitation; more water vapor in the atmosphere; earlier
river thaws; earlier spring migrations; plant blooms; etc.
• Humans are the cause of increasing greenhouse gases in the
atmosphere (CO2, methane, etc.). Humans also cause emissions of
items that tend to cool the planet (sulfate aerosols for example).
• Climate models using estimates of past forcings (GHG, aerosols,
solar, volcanoes) can simulate much of the past climate variations
at the global scale and many regional scales.
• Using estimates of future emissions, climate models project relatively
large increases in warming and other associated climate impacts
(precipitation, sea level, etc.) over the next century.
IPCC- How is it organized?
• Three Working Groups
I. Physical climate changes
II. Impacts of physical climate changes on
human and natural systems
III. Mitigation (cost/benefits) of future climate
changes
• Scientists assess peer-reviewed literature
– Role of consensus
– Role of uncertainty
IPCC- Role of consensus
• Finding consensus is a messy business
– Scientists seem much better at finding points
of disagreement than points of agreement
• Does a given statement reflect the
scientific literature, uncertainties and a
wide range of opinions?
IPCC- Role of consensus
• Wording is a big issue
• 2001 WGI bottom line as an example:
“There is new and stronger evidence that most
of the warming over the last 50 years is
attributable to human activities.”
– Plenary turned “much” into “most”
– Previous disagreement over
“substantial” resulted in “much”
• What does substantial mean?
• Majority?
• Plurality?
IPCC- Role of consensus
> Can I live with statement?
– Is statement wrong?
– In plenary this question can be very important
IPCC- Role of uncertainty
Different ways to express uncertainty
• Probability (pdf) – likelihood – WG1
– Virtually certain, Very likely, likely, etc.
• Confidence – high confidence – WG2
– High, medium, low confidence
• Agreement – high agreement – WG3
– High, medium, low agreement
• Evidence – much evidence – WG3
– Much, medium, limited evidence
IPCC- Role of uncertainty
• Working Group I definitions:
– Virtually certain: >99% probability (1:100)
– Extremely likely: >95% (1:20)
– Very likely: >90% (1:10)
– Likely: > 66% (1:3)
– More likely than not: >50%
– Unlikely: <33%
– Very unlikely: <10%
IPCC- Role of governments
• Must approve SPM (Summary for
PolicyMakers) line by line (or word by word)
• Scientists must also agree to wording
changes
– Must be consistent with underlying report
– “Can I live with wording?” question
• Possible to have footnotes saying that a
given country or countries did not approve of
a part of the text – never used to date … but
often threatened
IPCC- Plenary
Valencia, Spain November, 2007
IPCC- Plenary
• Typically go very slowly through text in the
beginning
• When progress stops on a
wording/science/political issue => breakout
groups
• Breakout groups meet before/after meeting
– Focus on a subset of the text
• Last day(s) goes well into night
– Rush to get things done
IPCC- Process (Author’s viewpoint)
•
•
•
•
•
Organizational meeting
Literature search and community input
Write 1st draft
Limited expert review
Second meeting
– Cross cutting issues between chapters
– Plan next draft
• Write 2nd draft
– Publication deadline for referenced papers
IPCC- Process (Author’s viewpoint)
• Deal with review comments (experts and
national review)
– Each must be answered
– Review and Comments made public
– More than 1000 comments per chapter
• 3rd authors meeting
– Cross cutting issues
– Deal with review/comments
• Write last draft
IPCC- Process (Author’s viewpoint)
• Deal with review comments (national and
NGO review)
– Each must be answered
– Review and Comments made public
– More than 1000 comments per chapter
• Write final version
– Cross chapter references
– Consistency between chapter and SPM
Projections of future climate
change
•
•
•
•
•
Review
Projections
Time scales of response
Variability
Abrupt climate change
Carbon
Dioxide
Methane
Important greenhouse
gases are increasing.
The largest increases
are in the last 100
years or so.
Nitrous
Oxide
IPCC WGI SPM
Over the last
100 years
the:
Surface
temperature
is increasing
Sea level is
rising
Snow cover is
decreasing
IPCC WGI SPM
Human
activities are
very likely the
cause of the
warming of
last 100
years.
Black line: temperature observation from thermometers.
Pink shade: Climate model simulations using all past radiative forcings.
Blue shade: Climate model simulation using only natural forcings (solar, volca
IPCC WGI SPM
Human
activities
are likely to
be the
cause of
the
warming
over last
100 years
on each
continent.
IPCC WGI SPM
Past IPCC Projections vs.
Observations
• Projections very
good – so far.
• Lots of issues:
- No aerosols in FAR
- No volcanoes in all
- Natural variability
large
IPCC AR4 WGI Chapter 1
Special Report on Emission Scenarios
(SRES, 2000) and Post-SRES scenarios
• Emissions depend on:
– Population
– Technological development
– Society’s “choices”
• No mitigation assumed
• Emissions differ in
beginning of this century
• Emissions very different by
end of century
Figure from AR4 Synthesis report
Projection of future changes
in climate
• Range of projections is
broadly consistent with
the TAR.
– Stronger climatecarbon cycle
feedbacks.
IPCC WGI SPM
Best estimate
and likely
uncertainty
range at 2100
• Projection - scenario
independent over
next several decades.
• Warming this century
much larger than last
century.
Warming greatest over land and at most high
northern latitudes and least over Southern
Ocean and parts of the North Atlantic Ocean
Surface Warming
Pattern
A1B, 2090-2099
relative to 1980-1999
• Continuing recent observed trends in contraction of snow covered area,
increases in thaw depth over most permafrost regions, and decrease in
sea ice extent
• In some projections using SRES scenarios, Arctic late-summer sea ice
disappears almost entirely by the latter part of the 21st century
IPCC WGI SPM
Projection of future changes
in climate – sea level
meters
Note:
• No upper bound
• No likelihood
• No best estimate
• Model based
estimate only, no
expert judgment
IPCC WGI SPM
Sea Level Rise Uncertainty
Why so large?
• Understanding of some important effects that
determine sea level rise is too limited
• Published literature lacking
• Climate-carbon cycle feedbacks
• Changes in ice sheet flow
IPCC AR4 Synthesis Report wording
Sea Level Rise Uncertainty
The projections include a
contribution due to increased ice
flow from Greenland and
Antarctica at the rates observed
for 1993-2003, but these flow
rates could increase or
decrease in the future.
Therefore the upper values of
the ranges given are not to be
considered upper bounds for
sea level rise.
If this contribution (the observed rates) were to grow
linearly with global average temperature change, the
upper ranges of sea level rise for SRES scenarios
would increase by 0.1 m to 0.2 m. {WGI 10.6, SPM}
IPCC AR4 Synthesis Report wording
Other examples of regional changes
• Very likely increase in frequency
of hot extremes, heat waves, and
heavy precipitation
• Likely increase in tropical cyclone
intensity; less confidence in
global decrease of tropical
cyclone numbers
• Poleward shift of extra-tropical
storm tracks with consequent
changes in wind, precipitation,
and temperature patterns
• Very likely precipitation increases
in high latitudes and likely
decreases in most subtropical
land regions, continuing
observed recent trends
IPCC WGI SPM
21st Century Water Availability (Runoff) Changes
(Annually averaged)
Drier
Wetter
• Very likely runoff will increase in high latitudes.
• Likely runoff will decrease over some subtropical
and tropical regions.
IPCC AR4 Synthesis
Time scales of Response
• Human and natural systems
• Physical climate system
– Greenhouse gas lifetimes in atmosphere
– Ocean
– Ice sheets
Response time scales
• Note response in 2020’s
very similar in spite of
very different emissions.
• Note response in 2090’s
much more scenario
dependent.
• Actions taken today only
have large impacts in
climate response in the
future.
Response time scales
Role of Oceans
Response time scales
Role of Oceans
Anthropogenic warming and
sea level rise would continue
for centuries, even if GHG
concentrations were to be
stabilized at or above today’s
levels.
IPCC WGI SPM
AR4 estimates 0.2 to 0.6m
sea level rise per oC at
equilibrium due only to
thermal expansion of sea
water.
What would 1 meter do?
Variability
How
“smooth” is
the future
temperature
increase?
• January 2008 is a cold month
• Drop as large as December to January fairly common
• Cause?
• La Nina
• Variability over NH continents
Anthropogenic warming could lead to some
impacts that are abrupt or irreversible,
depending upon the rate and magnitude of the
climate change.
• Partial loss of ice sheets on polar
land could imply meters of sea level
rise, major changes in coastlines
and inundation of low-lying areas,
with greatest effects in river deltas
and low-lying islands.
• Such changes are projected to
occur over millennial time scales,
but more rapid sea level rise on
century time scales cannot be
excluded.
IPCC WGI SPM
Anthropogenic warming could lead to some
impacts that are abrupt or irreversible
– Based on current model
simulations, the Meridional
Overturning Circulation (MOC) of
the Atlantic Ocean will very likely
slow down during the 21st
century; nevertheless
temperatures over the Atlantic
and Europe are projected to
increase.
– The MOC is very unlikely to
undergo a large abrupt transition
during the 21st century.
– Longer-term MOC changes
cannot be assessed with
confidence.
Summary
• The IPCC is a successful mechanism
communicating climate change science.
• The IPCC can influence policy through government
actions
– Importance of gov’t approval of SPMs
• The projections of climate change for this century
are larger than what has occurred in the past
century.
• Response time scales, natural variability complicate
discussion and hinder understanding.
• We know a lot about future climate changes, but
some surprises are expected.
Thank you
More systematic
understanding
of the timing and
magnitude of
impacts related
to differing
amounts and
rates of climate
change.
Water
There is high confidence that hundreds of millions of
people will be exposed to increased water stress
Ecosystems
There is high confidence that many species are at
increasing risk of extinction with increasing
temperature.
Food
Globally food production is projected to increase at
local temperature increases of 1-3 oC; decreases
projected above (medium confidence).
Coasts
There is high confidence that millions of people could
experience more coastal flooding if global temperature
increases more than 2C in this century.
Sea level has very long times and will continue to rise
for centuries after stabilization of GHG.
Health
The health status of millions of people is projected to be affected
through, for example:
• Increases in malnutrition
• Increased deaths, diseases and injury due to extreme weather events
• Increased burden of diarrhoeal diseases
• Increased frequency of cardio-respiratory diseases due to changes in air quality
• Altered spatial distribution of some infectious diseases.
Some regions are likely to be especially
affected
• The Arctic, because of the impacts of high
rates of projected warming on natural
systems and human communities
• Africa, because of low adaptive capacity
and projected climate change impacts
• Small islands, where there is high exposure
of population and infrastructure to projected
climate change impacts
• Asian and African megadeltas, due to large
populations and high exposure to sea level
rise, storm surges and river flooding.
Anthropogenic warming could lead to
some impacts that are abrupt or
irreversible
– There is medium confidence that
approximately 20-30% of species
assessed so far are likely to be at
increased risk of extinction if increases
in global average warming exceed 1.52.5oC (relative to 1980-1999).
– As global average temperature increase
exceeds about 3.5oC, model projections
suggest significant extinctions (40-70%
of species assessed) around the globe.