Download Climate Change 2007: The Physical Science Basis The

Climate Change 2007: The
Physical Science Basis
The Working Group I Report of the
Intergovernmental Panel on Climate Change
Fourth Assessment Report
Nathan Bindoff and others
ACECRC, IASOS, CSIRO MAR
University of Tasmania
TPAC
IASOS Seminar Series
The IPCC is a “remarkable
example” of mobilizing expert
analysis to inform policymakers
Jeffrey Sachs (Nature, 12 August 2004)
The IPCC assessments are “dull as
dishwater”
Tim Flannery, The Weather Makers
The structure
of the IPCC for
the Fourth
Assessment
Report
Co-chairs:
Susan Solomon, USA
Dahe Qin, China
HUMAN AND NATURAL DRIVERS OF
CLIMATE CHANGE
[Chapters 2,6,7]
Main Focus
 Long-term changes in the concentrations of the
major long-lived greenhouse gases (from ice
cores, firn data, direct atmospheric measurements)
 Radiative Forcing estimates due to the different
agents [1750-2005]
Current atmospheric concentrations of
carbon dioxide, methane and
nitrous oxide:
- exceed pre-industrial values;
- have increased markedly since 1750
due to human activities
Relatively little variation in
concentrations before
the industrial era.
Rapid rate of increase in
concentrations and forcing during the
industrial era
Carbon dioxide forcing increased
by 20% in the last 10 years
[Revised] Fig. SPM-1
RADIATIVE FORCING (RF) [1750-2005]
{Global-average estimates and ranges; typical geographical
extent and assessed level of scientific understanding}
ANTHROPOGENIC
Long-lived greenhouse gases
-dominant forcing, with high scientific understanding
Other greenhouse gases: ozone
Aerosol Direct forcing: better constrained since TAR
Best estimate for cloud albedo forcing given for first
time. Note large and asymmetric uncertainty range.
Land-surface forcings
{forcings less than +/- 0.1 Wm-2 not discussed}
NATURAL
Revised solar forcing less than half of that in TAR
- from re-evaluation of the change in the long-term
irradiance
[Revised] Fig. SPM-2
-Volcanic forcing not shown on figure as it is episodic
Since the TAR, improved understanding and better
quantification of the forcing mechanisms
 Combined anthropogenic forcing derived for the first
time using best estimate and uncertainty of each
forcing: not a simple sum of the individual best
estimates
 Globally-averaged combined anthropogenic radiative
forcing since 1750 is positive and causing warming
 Combined anthropogenic forcing much larger than that
due to solar irradiance change (a natural forcing)
Direct observations of changes in current climate
•
•
•
•
Global changes in atmospheres, oceans,
cryosphere and sea level.
Regional changes and changes in extremes
Climate variables that are unchanged
Paleoclimate support for current changes
Much more comprehensive than TAR
“Warming of the climate system is unequivocal, as is
now evident from observations of increases in
global average air and ocean temperatures,
widespread melting of snow and ice, and rising global
average sea level (see Figure SPM-3).”
Global mean temperatures are rising faster with time
Warmest 12 years:
1998,2005,2003,2002,2004,2006,
2001,1997,1995,1999,1990,2000
SPM-3a
Sea level is rising in 20th century
SPM-3b
Rates of sea level rise:
•1.8 + 0.5 mm yr-1, 1961-2003
•1.7 + 0.5 mm yr-1, 20th
Century
•3.1 + 0.7 mm yr-1, 1993-2003
Glacier contribution to sea-level since 1961
Increased glacier retreat
since the early nineties
Mass loss from glaciers
and ice caps:
• 0.5 ± 0.18 mm yr-1, 19612003
• 0.77 ± 0.22 mm yr-1, 19912003
Ice sheet contributions to sea level rise
Mass loss of Greenland:
• 0.05 ± 0.12 mm yr-1 SLE,
1961-2003
• 0.21 ± 0.07 mm yr-1 SLE,
1991-2003
Antarctic ice sheet loses mass
mostly through increased glacier
flow
Greenland mass loss is
increasing
Loss: glacier discharge, melting
Mass loss of Antarctica:
• 0.14 ± 0.41 mm yr-1 SLE,
1961-2003
• 0.21 ± 0.35 mm yr-1 SLE,
1991-2003
Accounting for observed sea level rise
1961-2003: Sea level
budget not quite
closed.
1993-2003: Sea level
budget is closed.
Snow cover is decreasing
SPM-3c
Spring snow cover shows 5% stepwise
drop during eighties
Direct Observations of Changes in Current Climate
Numerous changes at the scales of continents or
ocean basins including.
•wind,
•precipitation,
•ocean salinity,
•ice sheets,
•extreme weather.
Arctic vs Global annual temperature anomalies (°C)
Warming in the Arctic
is double that for the
globe from 19th to 21st
century and from late
1960s to present.
Warmth 1925 to 1950
in Arctic was not as
widespread as recent
global warmth.
Note different scales
Land precipitation is changing significantly over broad areas
Increases
Decreases
Smoothed annual anomalies for precipitation (%) over land from
1900 to 2005; other regions are dominated by variability.
Warm nights are increasing; cold nights decreasing
1979-2003
1951-1978
1901-1950
fewer
more
fewer
10th (left) and 90th (right) percentiles
more
Frequency of occurrence of cold or warm temperatures for 202
global stations with at least 80% complete data between 1901 and
2003 for 3 time periods:
1901 to 1950 (black), 1951 to 1978 (blue) and 1979 to 2003 (red).
Drought is increasing most places
The most
important spatial
pattern (top) of
the monthly
Palmer Drought
Severity Index
(PDSI) for 1900
to 2002.
The time series
(below) accounts
for most of the
trend in PDSI.
SPM-2. Assessment of human influence
Phenomenon and direction
of trend
Likelihood that trend
occurred in late 20th
century (typically post
1960)
Warmer and few er cold days
and nights over most land
areas.
Very likely
Warmer and more hot days
and nights over most land
areas.
a
Likelihood of a human
contribution to
observed trend
d
Likelihood of
continuation of trend
based on projections
for 21st century using
SRES scenarios.
b
Likely
d
Very likely
c
Likely (nights)
Warm spells / heat w aves.
Frequency increases over
most land areas.
Likely
More likely than not
f
Very likely
Heavy precipitation events.
Frequency (or proportion of
total rainfall from heavy falls)
increases over most areas.
Likely
More likely than not
f
Very likely
Area affected by droughts
increases.
Likely in ma ny regions
since 1970s
More likely than not
Likely
Intense tropical cyclone
activity increases.
Likely, in s ome regions
since 1970
More likely than not f
Likely
Increased incidence of
extreme high sea level
(excludes tsunamis).g
Likely
Virtually certain
d
More likely than not
d
Virtually certain
f,h
i
Likely
1
f. Magnitude of anthropogenic contributions not assessed. Attribution for these phenomena
based on expert judgment rather than formal attribution studies
Direct Observations of Changes in Current Climate
Some aspects of climate appear not to have
changed:
•day-night temperature differences (since 1979)
•Antarctic sea ice extent trends (since 1973)
A paleoclimatic perspective
Paleoclimate information for supports…..
•unusual nature of the recent warming in last 5001300 years
•past warming has driven large-scale ice sheet
retreat and past sea level rise.
A paleoclimate perspective
125,000 years ago, higher Arctic temperatures likely resulted in
sea level 4-6m above present - contributions may have come from both
Arctic Ice Fields (especially Greenland) and Antarctica
Simulated and observed Arctic
warming at 125,000 yr B.P.
Estimated reduction in Greenland
Ice Sheet Area and Thickness
Understanding and attributing
climate change
Summary for Policymakers
- To what extent are observed changes due to
external influences on climate?
- Equilibrium climate sensitivity
Observations
Attribution
• are observed
changes
consistent with
expected
responses to
forcings
inconsistent with
alternative
explanations
All forcing
Solar+volcanic
TS-23
Observations
• Anthropogenic
greenhouse gas
increases very
likely caused
most of the
observed
warming since
mid-20th century
All forcing
Solar+volcanic
TS-23
Continental warming
SPM-4
likely shows a
significant
anthropogenic
contribution
over the past 50
years
Observations
All forcing
natural forcing
Equilibrium Climate Sensitivity
warming following a sustained doubling of CO2 concentrations Surface
Best estimate 3°C;
likely 2-4.5°C;
very unlikely less than
1.5°C;
higher values
20th
constraints: observed
uncertainty, last 700 yrs
not ruled out
century warming, model
Projections of Future Changes in Climate (Chapters 10, 11)
Basis of Projections in AR4:
•
unprecedented coordinated experiments using AOGCMs from 16
groups (11 countries) and 23 models collected at PCMDI (31 TBytes)
•
hierarchy of independent models (SCMs, EMICs, AOGCMs)
•
new approaches and greater use of constraints from observations
Projections of Future Changes in Climate
Best estimate for
low scenario (B1)
is 1.8°C (likely
range is 1.1°C to
2.9°C), and for
high scenario
(A1FI) is 4.0°C
(likely range is
2.4°C to 6.4°C).
Broadly
consistent with
span quoted for
SRES in TAR, but
not directly
comparable
Projections of Future Changes in Climate (Chapters 10, 11)
Figure SPM-5,
TS-28, 10.8, 10.28
• Multi-model means of warming for near term (2020-2029) and end
of the 21st century (2090-2099)
• Likelihood can now be given for the range of global mean warming
by an assessment of multiple lines of evidence
• Higher confidence in projected patterns and regional-scale features
Projections of Future Changes in Climate (Chapters 10, 11)
Figure SPM-6, TS-30, 10.9
• Multi-model mean of precipitation %-change for a medium SRES
scenario (A1B) for 2090-2099
• Seasonal precipitation regimes with information on magnitude and
inter-model agreement
• Precipitation increases are very likely in high latitudes in 2090-2099
• Decreases are likely in most subtropical land regions in 2090-2099
Ch. 10, Fig. 10.15
Very likely that the Atlantic meridional overturning circulation (MOC) will slow
down over the course of the 21st century.
Very unlikely that the MOC will undergo a large abrupt transition during the 21st
century. Longer-term changes in the MOC cannot be assessed with confidence
Studies with additional fresh water from melting of the Greenland Ice Sheet
suggest that this will not lead to a complete MOC shutdown in the 21st century.
Projections of Future Changes in Climate (Chapters 10, 11)
Post 2100 changes, Greenland:
• “…..and that the surface mass balance becomes negative at a global average
warming (relative to pre-industrial values) in excess of 1.9 to 4.6°C. If a negative
surface mass balance were sustained for millennia, that would lead to virtually
complete elimination of the Greenland ice sheet and a resulting contribution to
sea level rise of about 7 m.”
Almost all marker scenarios exceed 1.9 to 4.6 °C tipping points
• “.. If radiative forcing were to be stabilized in 2100 at A1B levels11, thermal
expansion alone would lead to 0.3 to 0.8 m of sea level rise by 2300 (relative to
1980–1999). “
Implication, while not stated, is that there will be large sea level changes
beyond 2100 (eg by 2300 something like 1.5 to 3.5m)
The IPCC WGI “Headlines”
• “The balance of evidence suggests a discernible human
influence on global climate.” (SAR, 1995)
• “There is new and stronger evidence that most of the
warming observed over the last 50 years is attributable to
human activities.” (TAR, 2001)
• “Most of the observed increase in globally averaged
temperatures since the mid-20th century is very likely due
to the observed increase in anthropogenic greenhouse gas
concentrations.” (AR4, 2007)
• “Discernible human influences now extend to other aspects
of climate, including ocean warming, continental-average
temperatures, temperature extremes and wind patterns.”
(AR4, 2007)
Further IPCC information
• IPCC SPM www.ipcc.ch
• Royal Society Meeting, covering all IPCC
chapters, www.royalsoc.ac.uk
Projections of Future Changes in Climate (Chapters 10, 11)
Projection of sea level rise:
• Projections of sea level rise consist of contributions from five components.
• In the AOGCMs, thermal expansion provides the largest contributions to
sea level rise in the 21st century.
• Current ice sheet models have limitations in representing dynamical processes.
• Projections provide model-based ranges, and no estimate of their likelihood.
• Higher values cannot be quantified at this time, but cannot be ruled out.
Projection of changes in various components of the climate system:
• Higher confidence in projected changes of sea ice, snow cover, extreme
events, and other regional-scale features.
• Changes in the Atlantic meridional overturning circulation are now based on
multi-model means. Changes beyond the 21st century cannot be assessed
with confidence.
Projections of future climate changes, averaging periods
For A2 scenario:
TAR: 2071-2100 minus 1961-90 = 3.0°C
AR4 using TAR periods: 2071-2100 minus 1961-90 = 3.1°C
AR4 20 year periods: 2080-99 minus 1980-99 = 3.1°C
Some EMIC studies had only 2090-99 available; ten year
period is sufficient if averaged over enough models or for
large scale (e.g. global) quantities; also provide policyrelevant information for earlier century period 2020-29
AR4: 2090-99 minus 1980-99 = 3.4°C
New since TAR: best
estimates and likely range
assessed from multiple
models, with AOGCMs as
basis for best estimate;
widely quoted TAR ranges
based only on one simple
model
higher uncertainty on the
warm side due to carbon
cycle uncertainties
Only results from A2 can be directly compared to TAR (average warming in
early and late century nearly identical, ranges mostly reduced in AR4 due to
model improvements and new and better constraints on climate sensitivity):
TAR (9 AOGCMs)
2071-2100 minus 1961-90 = 3.0°C (model range 1.3°C-4.5°C)
2021-2050 minus 1961-90 = 1.1°C (model range 0.5°C-1.4°C)
AR4 (17 AOGCMs)
2071-2100 minus 1961-90 = 3.1°C (model range 2.3°C-3.7°C)
2021-2050 minus 1961-90 = 1.0°C (model range 1.0°C-1.6°C)
[2090-99 minus 1980-99 = 3.2°C (full assessed range 1.9°C-5.1°C)]
Projections of future climate changes, averaging periods
For A2 scenario:
TAR: 2071-2100 minus 1961-90 = 3.0°C
AR4 using TAR periods: 2071-2100 minus 1961-90 = 3.1°C
AR4 20 year periods: 2080-99 minus 1980-99 = 3.1°C
Some EMIC studies had only 2090-99 available; ten year
period is sufficient if averaged over enough models or for
large scale (e.g. global) quantities; also provide policyrelevant information for earlier century period 2020-29
AR4: 2090-99 minus 1980-99 = 3.4°C
New since TAR: best
estimates and likely range
assessed from multiple
models, with AOGCMs as
basis for best estimate;
widely quoted TAR ranges
based only on one simple
model
higher uncertainty on the
warm side due to carbon
cycle uncertainties
Only results from A2 can be directly compared to TAR (average warming in
early and late century nearly identical, ranges mostly reduced in AR4 due to
model improvements and new and better constraints on climate sensitivity):
TAR (9 AOGCMs)
2071-2100 minus 1961-90 = 3.0°C (model range 1.3°C-4.5°C)
2021-2050 minus 1961-90 = 1.1°C (model range 0.5°C-1.4°C)
AR4 (17 AOGCMs)
2071-2100 minus 1961-90 = 3.1°C (model range 2.3°C-3.7°C)
2021-2050 minus 1961-90 = 1.0°C (model range 1.0°C-1.6°C)
[2090-99 minus 1980-99 = 3.2°C (full assessed range 1.9°C-5.1°C)]
Ch. 10, Supplementary Fig. S10.1
Snow area
limit
Snow
area
difference
Decreases of snow area and depth in a future
warmer climate
Multi-model mean area average of snow cover
fraction, % change ± 1 cross-model standard
deviation (2020-29 minus 1980-99)/1989-99;
2080-99 minus 1980-99)/1989-99 :
avg NH
Early 21st century
Commit -3.2% ± 2.7%
B1
Snow
depth
difference
late 21st century
-4.2% ± 3.8%
-5.8% ± 3.4%
-13.3% ± 6.6%
A1B -5.8% ± 3.5%
-18.3% ± 8.7%
A2
-22.9% ± 8.8%
-5.8% ± 3.4%
Projections of future climate changes, averaging periods
For A2 scenario:
TAR: 2071-2100 minus 1961-90 = 3.0°C
AR4 using TAR periods: 2071-2100 minus 1961-90 = 3.1°C
AR4 20 year periods: 2080-99 minus 1980-99 = 3.1°C
Some EMIC studies had only 2090-99 available; ten year
period is sufficient if averaged over enough models or for
large scale (e.g. global) quantities; also provide policyrelevant information for earlier century period 2020-29
AR4: 2090-99 minus 1980-99 = 3.4°C
New since TAR: best
estimates and likely range
assessed from multiple
models, with AOGCMs as
basis for best estimate;
widely quoted TAR ranges
based only on one simple
model
higher uncertainty on the
warm side due to carbon
cycle uncertainties
Only results from A2 can be directly compared to TAR (average warming in
early and late century nearly identical, ranges mostly reduced in AR4 due to
model improvements and new and better constraints on climate sensitivity):
TAR (9 AOGCMs)
2071-2100 minus 1961-90 = 3.0°C (model range 1.3°C-4.5°C)
2021-2050 minus 1961-90 = 1.1°C (model range 0.5°C-1.4°C)
AR4 (17 AOGCMs)
2071-2100 minus 1961-90 = 3.1°C (model range 2.3°C-3.7°C)
2021-2050 minus 1961-90 = 1.0°C (model range 1.0°C-1.6°C)
[2090-99 minus 1980-99 = 3.2°C (full assessed range 1.9°C-5.1°C)]
Thomas will show this first, then I will show it again using his slide; I’ll
show SPM-5 building on what Thomas showed for eq clim sens, and
TCR, and 10.29 (below)
Structure of IPCC AR4 Assessment
• 3 Working Group Reports:
– Full Reports
• Each ~1000 pages
• Extensive expert and government review
• “Accepted” by IPCC Working Group
– Technical Summaries
• Typically 60 pages
– Summaries for Policy Makers
• 5-20 pages
• Detailed expert & government review
• “Approved” line-by-line by Working Group
• Synthesis Report
– Synthesizes the 3 WG reports
– About 30 pages, with 5 page SPM
– “Approved” line-by-line by IPCC Panel, November 2007
WGI AR4 Schedule
•
•
•
•
•
•
•
•
•
•
May 2004: Author teams selected
September 2004: 1st Lead Author meeting, Trieste
February 2005: Informal review of preliminary draft
May 2005: 2nd LA meeting, Beijing
September 2005: External review of 1st draft begins
December 2005: 3rd LA meeting, Christchurch
April 2006: External and government review of 2nd draft
June 2006: 4th LA meeting, Bergen
October 2006: Final draft to governments - SPM review
February 2007: WGI plenary (Paris) approves/accepts
documents
1.
2.
3.
4.
5.
6.
7.
WGI:
The
Physical
Science
Basis
Historical overview of climate change science
Changes in atmospheric constituents and in radiative forcing
Observations: Surface and atmospheric climate change
Observations: Changes in snow, ice and frozen ground
Observations: Oceanic climate change and sea level
Paleoclimate
Couplings between changes in the climate system and
biogeochemistry
8. Climate models and their evaluation
9. Understanding and attributing climate change
10. Global climate projections
11. Regional climate projections
Australian lead authors, WGI
• Ian Allison (Antarctic Division; Chapter 4, “Observations:
Changes in snow, ice and frozen ground”)
• Nathan Bindoff (Antarctic Climate & Ecosystems CRC;
Chapter 5: “Observations: Oceanic climate change and sea
level”)
• Robert Colman (BMRC) & Andrew Pitman (Macquarie
University; Chapter 8, “Climate models and their
evaluation”)
• Neville Nicholls (Monash Univ., Chapter 9,
“Understanding and attributing climate change”)
• Ian Watterson (CSIRO Atmospheric Research, Chapter 10:
“Global climate projections”)
• Penny Whetton (CSIRO Atmospheric Research; Chapter
11, “Regional climate projections”).
WGI: Chapter 9 “Understanding and
attributing climate change”
•
Number of review comments received:
–
–
•
•
1438 on First Draft
1157 on Second Draft (~ 50% from one reviewer)
All comments are electronically archived (with
name of reviewer)
Responses to all comments are electronically
archived
“Global atmosphericﾊconcentrations of carbon dioxide,
methane and nitrous oxide …now far exceed preindustrial values determined from ice cores..”.
Some common questions
• Was the approval process worth the effort?
• Was it (the SPM) written by scientists or
politicians or bureaucrats?
• Am I relieved it is over?
• Was it fun?
Progress since the TAR
Circulation change
• Anthropogenic
forcing has likely
contributed
• Affecting storm
tracks, winds and
temperature
patterns
TS Box 3.1
Equilibrium climate sensitivity
Surface warming following a sustained doubling of CO2 concentrations
very unlikely below
1.5°C
most likely ~ 3°C
likely range is
2°C to 4.5°C
TS-25
constraints: observed 20th century warming, model
uncertainty, last 700 yrs