IASOS Seminar Series 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

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 [ ]

Current atmospheric concentrations of carbon dioxide, methane and nitrous oxide: - exceed pre-industrial values; - have increased markedly since 1750 due to human activities [Revised] Fig. SPM-1 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

RADIATIVE FORCING (RF) [ ] {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 -Volcanic forcing not shown on figure as it is episodic [Revised] Fig. SPM-2

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)

“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).” 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

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 20 th century Rates of sea level rise: mm yr -1, mm yr-1, 20 th Century mm yr -1, SPM-3b

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, ± 0.22 mm yr -1,

Ice sheet contributions to sea level rise Antarctic ice sheet loses mass mostly through increased glacier flow Greenland mass loss is increasing Loss: glacier discharge, melting Mass loss of Greenland: 0.05 ± 0.12 mm yr -1 SLE, ± 0.07 mm yr -1 SLE, Mass loss of Antarctica: 0.14 ± 0.41 mm yr -1 SLE, ± 0.35 mm yr -1 SLE,

Accounting for observed sea level rise : Sea level budget not quite closed : Sea level budget is closed.

Snow cover is decreasing Spring snow cover shows 5% stepwise drop during eighties SPM-3c

Numerous changes at the scales of continents or ocean basins including. wind, precipitation, ocean salinity, ice sheets, extreme weather. Direct Observations of Changes in Current Climate

Warming in the Arctic is double that for the globe from 19 th to 21 st century and from late 1960s to present. Warmth 1925 to 1950 in Arctic was not as widespread as recent global warmth. Note different scales Arctic vs Global annual temperature anomalies (°C)

Smoothed annual anomalies for precipitation (%) over land from 1900 to 2005; other regions are dominated by variability. Land precipitation is changing significantly over broad areas Increases Decreases

10 th (left) and 90 th (right) percentiles 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) Warm nights are increasing; cold nights decreasing  fewer more 

The most important spatial pattern (top) of the monthly Palmer Drought Severity Index (PDSI) for 1900 to The time series (below) accounts for most of the trend in PDSI. Drought is increasing most places

f. Magnitude of anthropogenic contributions not assessed. Attribution for these phenomena based on expert judgment rather than formal attribution studies SPM-2. Assessment of human influence

Some aspects of climate appear not to have changed: day-night temperature differences (since 1979) Antarctic sea ice extent trends (since 1973) Direct Observations of Changes in Current Climate

Paleoclimate information for supports….. unusual nature of the recent warming in last years past warming has driven large-scale ice sheet retreat and past sea level rise. A paleoclimatic 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 A paleoclimate perspective

Understanding and attributing climate change Summary for Policymakers - To what extent are observed changes due to external influences on climate? - Equilibrium climate sensitivity

Attribution are observed changes consistent with expected responses to forcings  inconsistent with alternative explanations Observations All forcing Solar+volcanic TS-23

Anthropogenic greenhouse gas increases very likely caused most of the observed warming since mid-20 th century Observations All forcing Solar+volcanic TS-23

Continental warming likely shows a significant anthropogenic contribution over the past 50 years Observations All forcingnatural forcing SPM-4

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 not ruled out constraints: observed 20 th century warming, model uncertainty, last 700 yrs

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 (Chapters 10, 11)

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

Multi-model means of warming for near term ( ) and end of the 21 st century ( ) 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 Figure SPM-5, TS-28, 10.8, Projections of Future Changes in Climate (Chapters 10, 11)

Multi-model mean of precipitation %-change for a medium SRES scenario (A1B) for Seasonal precipitation regimes with information on magnitude and inter-model agreement Precipitation increases are very likely in high latitudes in Decreases are likely in most subtropical land regions in Figure SPM-6, TS-30, 10.9 Projections of Future Changes in Climate (Chapters 10, 11)

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 21 st century. Ch. 10, Fig

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) Projections of Future Changes in Climate (Chapters 10, 11)

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 Royal Society Meeting, covering all IPCC chapters,

Projection of sea level rise: Projection of changes in various components of the climate system: 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 21 st 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. 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 21 st century cannot be assessed with confidence. Projections of Future Changes in Climate (Chapters 10, 11)

Projections of future climate changes, averaging periods For A2 scenario: TAR: minus = 3.0°C AR4 using TAR periods: minus = 3.1°C AR4 20 year periods: minus = 3.1°C Some EMIC studies had only available; ten year period is sufficient if averaged over enough models or for large scale (e.g. global) quantities; also provide policy- relevant information for earlier century period AR4: minus = 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) minus = 3.0°C (model range 1.3°C-4.5°C) minus = 1.1°C (model range 0.5°C-1.4°C) AR4 (17 AOGCMs) minus = 3.1°C (model range 2.3°C-3.7°C) minus = 1.0°C (model range 1.0°C-1.6°C) [ minus = 3.2°C (full assessed range 1.9°C-5.1°C)]

Projections of future climate changes, averaging periods For A2 scenario: TAR: minus = 3.0°C AR4 using TAR periods: minus = 3.1°C AR4 20 year periods: minus = 3.1°C Some EMIC studies had only available; ten year period is sufficient if averaged over enough models or for large scale (e.g. global) quantities; also provide policy- relevant information for earlier century period AR4: minus = 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) minus = 3.0°C (model range 1.3°C-4.5°C) minus = 1.1°C (model range 0.5°C-1.4°C) AR4 (17 AOGCMs) minus = 3.1°C (model range 2.3°C-3.7°C) minus = 1.0°C (model range 1.0°C-1.6°C) [ minus = 3.2°C (full assessed range 1.9°C-5.1°C)]

Ch. 10, Supplementary Fig. S10.1 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 ( minus )/ ; minus )/ : avg NH Early 21 st century late 21 st century Commit -3.2% ± 2.7% -4.2% ± 3.8% B1 -5.8% ± 3.4% -13.3% ± 6.6% A1B -5.8% ± 3.5% -18.3% ± 8.7% A2 -5.8% ± 3.4% -22.9% ± 8.8% Snow area limit Snow area difference Snow depth difference

Projections of future climate changes, averaging periods For A2 scenario: TAR: minus = 3.0°C AR4 using TAR periods: minus = 3.1°C AR4 20 year periods: minus = 3.1°C Some EMIC studies had only available; ten year period is sufficient if averaged over enough models or for large scale (e.g. global) quantities; also provide policy- relevant information for earlier century period AR4: minus = 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) minus = 3.0°C (model range 1.3°C-4.5°C) minus = 1.1°C (model range 0.5°C-1.4°C) AR4 (17 AOGCMs) minus = 3.1°C (model range 2.3°C-3.7°C) minus = 1.0°C (model range 1.0°C-1.6°C) [ minus = 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 (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: 1 st Lead Author meeting, Trieste February 2005: Informal review of preliminary draft May 2005: 2 nd LA meeting, Beijing September 2005: External review of 1 st draft begins December 2005: 3 rd LA meeting, Christchurch April 2006: External and government review of 2 nd draft June 2006: 4 th LA meeting, Bergen October 2006: Final draft to governments - SPM review February 2007: WGI plenary (Paris) approves/accepts documents

WGI: The Physical Science Basis 1.Historical overview of climate change science 2.Changes in atmospheric constituents and in radiative forcing 3.Observations: Surface and atmospheric climate change 4.Observations: Changes in snow, ice and frozen ground 5.Observations: Oceanic climate change and sea level 6.Paleoclimate 7.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 pre- industrial 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

very unlikely below 1.5°C most likely ~ 3°C likely range is 2°C to 4.5°C Equilibrium climate sensitivity constraints: observed 20 th century warming, model uncertainty, last 700 yrs Surface warming following a sustained doubling of CO2 concentrations TS-25