Human Influence? How Do We Know?

Transcription

1 Human Infuence? How Do We Know? Ben Santer Program for Cimate Mode Diagnosis and Intercomparison Lawrence Livermore Nationa Laboratory, Livermore, CA Emai: Cimate Change Science Workshop Fied Museum, Chicago, IL Apri 18 th,

2 Truth in advertising: Who do I work for? PCMDI: Program for Cimate Mode Diagnosis and Intercomparison Service: Coordinate internationa cimate modeing simuations (standard benchmark experiments) Enabe broader science community to anayze and evauate modes Goa: Quantify how we modes simuate present-day cimate and evauate uncertainty in projections of future cimate change PCMDI was estabished in 1989 Has been at Lawrence Livermore Nationa Lab since then 2

3 Detection and attribution research has made important contributions to the concusions of IPCC assessments The baance of evidence suggests a discernibe human infuence on goba cimate There is new and stronger evidence that most of the warming observed over the ast 50 years is attributabe to human activities Most of the observed increase in gobay averaged temperatures since the mid-20 th th century is very ikey* due to the observed increase in anthropogenic greenhouse gas concentrations 3

4 Structure of tak Cimate change 101 What is cimate change detection and attribution? Why is it important? How do we study the causes of cimate change? What is fingerprinting? Fingerprinting exampes Are there Inconvenient observations? Looking towards the future Concusions 4

5 Cimate Change 101: Natura mechanisms infuence cimate Natura mechanisms Changes in the Sun Changes in the amount of vocanic dust in the atmosphere Interna variabiity of the couped atmosphere-ocean system 5

6 Cimate Change 101: Human factors aso infuence cimate Non-natura mechanisms Changes in atmospheric concentrations of greenhouse gases Changes in aeroso partices from burning fossi fues and biomass Changes in the refectivity (abedo) of the Earth s surface Smoke from fires in Guatemaa and Mexico (May 14, 1998) 6

7 Cimate Change 101: Computer modes can perform the contro experiment that we can t do in the rea word Average surface temperature change ( C) Meeh et a., Journa of Cimate (2004) 7

8 Cimate Change 101: We routiney test how we current cimate modes simuate: Today s annua average cimate The daiy cyce The seasona cyce The response to massive vocanic eruptions Ocean uptake of products of atmospheric tests of nucear weapons The cimate changes of the past 30 to 150 years Cimates of the deep past (e.g., the ast Ice Age) Weather Modes of natura cimate variabiity (ike E Niño) 8

9 Structure of tak 9

10 Detection and attribution defined Detection of cimate change The process of showing that an observed change is highy unusua in a statistica sense Attribution of cimate change The process of estabishing cause and effect reationships 10

11 Why is detection and attribution work important? It is another form of mode evauation Successfu simuation of historica changes in cimate enhances our confidence in projections of future cimate change In an environment where there is sti poitica debate regarding the reaity of human effects on goba cimate, it is imperative to have sound science on the nature and causes of cimate change 11

12 Structure of tak 12

13 Mutipe ines of evidence on which discernibe human infuence concusions are based 1. Basic physics evidence Physica understanding of the cimate system and the heat-trapping properties of greenhouse gases 2. Circumstantia evidence Quaitative agreement between observed cimate changes and mode predictions of human-caused cimate changes (warming of oceans, and surface and troposphere, water vapor increases, etc.) 3. Paeocimate evidence Temperature reconstructions enabe us to pace the warming of the 20th century in a onger-term context 4. Fingerprint evidence Rigorous statistica comparisons between modeed and observed patterns of cimate change 13

14 What is cimate fingerprinting? Strategy: Search for a computer mode-predicted pattern of cimate change (the fingerprint ) in observed cimate records Assumption: Each factor that infuences cimate has a unique signature in cimate records Method: Standard signa processing techniques Advantage: Fingerprinting aows researchers to make rigorous tests of competing hypotheses regarding the causes of recent cimate change 14

15 Structure of tak 15

16 Understanding different fingerprints: The case of the Sun Pressure (hpa) N 0 N 660N 0 N 330N 0 N Eq E q 330S 0 S 660S 0 S 990S 0 S N N N. 4 E0 q S S S Height above Earth s surface (kiometers) Temperature change (degrees Cesius per century)

17 Different factors that infuence cimate have different fingerprints 1. Soar 3. We-mixed greenhouse gases Pressure (hpa) Pressure (hpa) N 0 N 60N 0 N 330N 0 N Eq q 330S 0 S 60S 0 S 90S 0 S Santer et a., CCSP Report (2006) N 0 N 60N6 0 N 30N3 0 N EqE q 30S3 0 S 60S6 0 S 90S9 0 S Sufate aeroso partices Pressure (hpa) N 0 N 60N6 0 N 30N 0 N EqE q 30S3 0 S 60S6 0 S 90S9 0 S N 0 N 60N6 0 N 30N 0 N EqE q 30S3 0 S 60S6 0 S 90S9 0 S N9 0 N 60N6 0 N 30N3 0 N EqE q 30S3 0 S 60S6 0 S 90S9 0 S Height (km) 0. 4 C/century Height (km) Height (km) 2. Vocanoes 4. Ozone 17

18 Fingerprinting with temperature changes in Earth s atmosphere Mode Changes: CO 2 + Sufate Aerosos + Stratospheric Ozone Pressure (hpa) Height (km) N 45N 30N 15N 0 15S 30S 45S 60S 2 50 Observed Changes 18 Pressure (hpa) Height (km) N 45N 30N 15N 0 15S 30S 45S 60S 2 Santer et a., Nature (1996) Temperature changes in o C 18

19 Mythoogy 101: Changes in the Sun s energy output expain ALL observed warming CCSP Unified Synthesis Product (2009) 19

20 Fingerprinting in the ocean: Warming of the word s oceans over Red Green Bue Observed Mode run with human factors Mode contro run Depth (meters) Temperature change ( C) Barnett et a., Science (2005) 20

21 Fingerprinting in the ocean: Warming of the word s oceans over Green = Mode run with human factors Bue = Mode contro run Temperature change ( C) Depth (m) Depth (m) Depth (m) Red = Observed Temperature change ( C) Depth (m) Depth (m) Depth (m) Temperature change ( C) Temperature change ( C) Temperature change ( C) Temperature change ( C) 21 Barnett Barnett et et a., a., Science Science (2005) (2005)

22 Fingerprinting with changes in the amount of water vapor over oceans Santer et a., PNAS (2007) 22

23 The cimate system is teing us a physicay-consistent story. We have identified human fingerprints in 23

24 We ve moved beyond temperature ony fingerprint detection studies 24

25 Structure of tak 25

26 No history of detection and attribution work woud be compete without discussion of the great MSU debate Inconvenient observations the apparent ack of tropospheric warming in sateite data sateite measurements over 35 years show no significant warming in the ower atmosphere, which is an essentia part of the goba-warming theory. James Schesinger (former U.S. Secretary of Energy, Secretary of Defense, and Director of the CIA), Cod Facts on Goba Warming, L.A. Times, January 22,

27 Using microwave sounders to measure atmospheric temperature from space Figure and text courtesy of Car Mears, RSS Higher temperatures = more microwave emissions from oxygen moecues By choosing different microwave frequencies, different ayers in the atmosphere can be measured Much of the scientific focus has been on measurements of the temperature of the owest 7 8 km of the atmosphere 27

28 Which groups have been invoved in constructing Cimate Data Records from MSU information? 28

29 The UAH sateite dataset impied that the troposphere cooed as the tropica surface warmed 29

30 The RSS sateite data showed that the troposphere warmed by more than the surface 30

31 What factors contribute to these differences? Loca measurement time for each sateite drifts due to orbita drift This eads to drifts in the samping of the Earth s daiy temperature cyce These drifts need to be removed, or they can affect ong-term trends Ascending LECT (Hrs.) NOAA-6 NOAA-8 NOAA-10 NOAA-12 NOAA-6 TIROS-N NOAA-7 NOAA-9 NOAA-11 NOAA Year Figure and text courtesy of Car Mears, RSS 31

32 Three papers in Science partiay resoved the great MSU debate An eary sateite-based anaysis of the temperature of the tropica troposphere has a spurious cooing trend Weather baoon estimates of the temperature of the tropica troposphere aso contain a spurious cooing trend When errors in the sateite and weather baoon data are accounted for, both modes and observations show warming of the tropica troposphere reative to the surface 32

33 Resoution? Previousy reported discrepancies between the amount of warming near the surface and higher in the atmosphere have been used to chaenge the reiabiity of cimate modes and the reaity of human-induced goba warming This significant discrepancy no onger exists (from Preface of U.S. Cimate Change Science Program Report, May 2006) 33

34 Structure of tak 34

35 Looking towards the future In a post-ipcc AR4 word, is the science done and dusted? What wi the roe of detection and attribution research be in AR5? 35

36 Key scientific issues for future detection and attribution ( D&A ) studies 1. Most fingerprint work has focused on goba-scae changes in individua, primary cimate variabes Can we identify human effects on cimate at continenta to regiona scaes? Can we identify human fingerprints in variabes of direct reevance to cimatechange impacts? (e.g., timing of stream fow, snowpack depth) Can we attribute shifts in the distributions of pant and anima species to human infuences? (the doube attribution probem) 36

37 Key scientific issues for future detection and attribution ( D&A ) studies 2. We now ive in a muti-mode word, yet most D&A studies to date have been performed with individua modes Is it a mode democracy ( One mode, one vote? ) Or shoud we pay more attention to modes that do a better job in capturing aspects of present-day cimate that we care about? 37

38 Key scientific issues for future detection and attribution ( D&A ) studies 3. We cannot confidenty attribute any specific extreme event to humaninduced cimate change But can we make informed scientific statements about the infuence of human activities on the ikeihood of extreme events? (the operationa attribution issue) 38

39 Evauation of Fractiona Attributabe Risk Risk of European heat-wave exceeding 1.6 C thresho d with and without human infuence (Stott, Stone, and Aen, Nature, 2004) 0.8 Estimated ikeihood Average simuation omitting human infuence Average mode simuation with combined human and natura effects Number of occurrences per 1,000 years 39

40 Evauation of Fractiona Attributabe Risk Risk of European heat-wave exceeding 1.6 C thresho d with and without human infuence (Stott, Stone, and Aen, Nature, 2004) 0.8 Estimated ikeihood Average simuation omitting human infuence Average mode simuation with combined human and natura effects Number of occurrences per 1,000 years Can we do this type of anaysis with other extreme events? 40

41 Structure of tak 41

42 Concusions We have identified human fingerprints in a number of different aspects of the cimate system We have moved beyond temperature ony detection and attribution Criticisms eveed at IPCC Second Assessment Report ( you are ony ooking at surface temperature changes ) are no onger vaid The cimate system is teing us a physicay- and internay-consistent story The story s message: Natura causes aone cannot expain the observed changes Many scientists at dozens of universities and research institutions around the word have heped to te this story 42