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The IPCC Assessment Process: Future Projections of Climate Change

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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 ... – PowerPoint PPT presentation

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Title: The IPCC Assessment Process: Future Projections of Climate Change


1
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.
2
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
    human-induced climate change, its potential
    impacts and options for adaptation and
    mitigation.

3
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.
4
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.

5
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

6
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?

7
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?

8
IPCC- Role of consensus
  • gt Can I live with statement?
  • Is statement wrong?
  • In plenary this question can be very important

9
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

10
IPCC- Role of uncertainty
  • Working Group I definitions
  • Virtually certain gt99 probability (1100)
  • Extremely likely gt95 (120)
  • Very likely gt90 (110)
  • Likely gt 66 (13)
  • More likely than not gt50
  • Unlikely lt33
  • Very unlikely lt10

11
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

12
IPCC- Plenary
Valencia, Spain November, 2007
13
IPCC- Plenary
  • Typically go very slowly through text in the
    beginning
  • When progress stops on a wording/science/political
    issue gt 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

14
IPCC- Process (Authors 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

15
IPCC- Process (Authors 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

16
IPCC- Process (Authors 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

17
Projections of future climate change
  • Review
  • Projections
  • Time scales of response
  • Variability
  • Abrupt climate change

18
Important greenhouse gases are increasing. The
largest increases are in the last 100 years or so.
Carbon Dioxide
Methane
Nitrous Oxide
IPCC WGI SPM
19
Over the last 100 years the Surface temperature
is increasing Sea level is rising Snow cover
is decreasing
IPCC WGI SPM
20
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, volcanoes).
IPCC WGI SPM
21
Human activities are likely to be the cause of
the warming over last 100 years on each
continent.
IPCC WGI SPM
22
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
23
Special Report on Emission Scenarios (SRES, 2000)
and Post-SRES scenarios
  • Emissions depend on
  • Population
  • Technological development
  • Societys choices
  • No mitigation assumed
  • Emissions differ in beginning of this century
  • Emissions very different by end of century

Figure from AR4 Synthesis report
24
Projection of future changes in climate
  • Range of projections is broadly consistent with
    the TAR.
  • Stronger climate-carbon cycle feedbacks.
  • Projection - scenario independent over next
    several decades.
  • Warming this century much larger than last
    century.

Best estimate and likely uncertainty range at 2100
IPCC WGI SPM
25
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
26
Projection of future changes in climate sea
level
  • Note
  • No upper bound
  • No likelihood
  • No best estimate
  • Model based estimate only, no expert judgment

meters
IPCC WGI SPM
27
Sea Level Rise UncertaintyWhy 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
28
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
29
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
30
21st Century Water Availability (Runoff)
Changes (Annually averaged)
Wetter
Drier
  • Very likely runoff will increase in high
    latitudes.
  • Likely runoff will decrease over some subtropical
    and tropical regions.

IPCC AR4 Synthesis
31
Time scales of Response
  • Human and natural systems
  • Physical climate system
  • Greenhouse gas lifetimes in atmosphere
  • Ocean
  • Ice sheets

32
Response time scales
  • Note response in 2020s very similar in spite of
    very different emissions.
  • Note response in 2090s much more scenario
    dependent.
  • Actions taken today only have large impacts in
    climate response in the future.

33
Response time scalesRole of Oceans
34
Anthropogenic warming and sea level rise would
continue for centuries, even if GHG
concentrations were to be stabilized at or above
todays levels. AR4 estimates 0.2 to 0.6m sea
level rise per oC at equilibrium due only to
thermal expansion of sea water.
Response time scalesRole of Oceans
IPCC WGI SPM
35
What would 1 meter do?
36
Variability
How smooth is the future temperature increase?
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  • January 2008 is a cold month
  • Drop as large as December to January fairly
    common
  • Cause?
  • La Nina
  • Variability over NH continents

45
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
46
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.

47
Summary
  • The IPCC is a successful mechanism communicating
    climate change science.
  • The IPCC can influence policy through government
    actions
  • Importance of govt 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.

48
Thank you
49
More systematic understanding of the timing and
magnitude of impacts related to differing amounts
and rates of climate change.
50
Water There is high confidence that hundreds of
millions of people will be exposed to increased
water stress
51
Ecosystems There is high confidence that many
species are at increasing risk of extinction with
increasing temperature.
52
Food Globally food production is projected to
increase at local temperature increases of 1-3
oC decreases projected above (medium confidence).
53
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.
54
  • 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.

55
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.

56
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 1.5-2.5oC
    (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.

57
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