Current Update on Climate Science

Transcription

1 Current Update on Climate Science Ben Santer Program for Climate Model Diagnosis and Intercomparison Lawrence Livermore National Laboratory, Livermore, CA rd Annual CAFE Electric Aircraft Symposium Hiller Aviation Museum, San Carlos, California April 24 th,

2 Truth in advertising: Who do I work for? PCMDI: Program for Climate Model Diagnosis and Intercomparison Service: Coordinate international climate modeling simulations (standard benchmark experiments) Enable broader science community to analyze and evaluate models Goal: Quantify how well models simulate present-day climate and evaluate uncertainty in projections of future climate change PCMDI was established in 1989 Has been at Lawrence Livermore National Lab since then 2

3 Structure of talk Climate change 101 A brief review of climate fingerprinting Update on recent changes in greenhouse gases Update on recent changes in climate (and projections of future changes) Update on fingerprint research Conclusions 3

4 Climate Change 101: Natural mechanisms influence climate Natural mechanisms Changes in the Sun Changes in the amount of volcanic dust in the atmosphere Internal variability of the coupled atmosphere-ocean system 4

5 Climate Change 101: Human factors also influence climate Non-natural mechanisms Changes in atmospheric concentrations of greenhouse gases Changes in aerosol particles from burning fossil fuels and biomass Changes in the reflectivity (albedo) of the Earth s surface Smoke from fires in Guatemala and Mexico (May 14, 1998) 5

6 Average surface temperature change ( C) Climate Change 101: Computer models can perform the control experiment that we can t do in the real world Meehl et al., Journal of Climate (2004) 6

7 Climate Change 101: We routinely test how well current climate models simulate: Today s annual average climate The daily cycle The seasonal cycle The response to massive volcanic eruptions Ocean uptake of products of atmospheric tests of nuclear weapons The climate changes of the past 30 to 150 years Climates of the deep past (e.g., the last Ice Age) Weather Modes of natural climate variability (like El Niño) 7

8 Structure of talk Climate change 101 A brief review of climate fingerprinting Update on recent changes in greenhouse gases Update on recent changes in climate (and projections of future changes) Update on fingerprint research Conclusions 8

9 What is climate fingerprinting? Strategy: Search for a computer model-predicted pattern of climate change (the fingerprint ) in observed climate records Assumption: Each factor that influences climate has a unique signature in climate records Method: Standard signal processing techniques Advantage: Fingerprinting allows researchers to make rigorous tests of competing hypotheses regarding the causes of recent climate change 9

10 Pressure (hpa) Height above Earth s surface (kilometers) Understanding different fingerprints: The case of the Sun N 60N 30N Eq 30S 60S 90S N N N Eq S S S Temperature change (degrees Celsius per century)

11 Pressure (hpa) Height (km) Pressure (hpa) Height (km) Pressure (hpa) Height (km) Different factors that influence climate have different fingerprints 1. Solar 3. Well-mixed greenhouse gases N 60N 30N Eq 30S 60S 90S N 60N 30N Eq 30S 60S 90S Sulfate aerosol particles Santer et al., CCSP Report (2006) N 60N 30N N 60N 30N N 60N 30N Eq 30S 60S 90S Eq 30S 60S 90S Eq 30S 60S 90S C/century Volcanoes 4. Ozone 11

12 Pressure (hpa) Height (km) Pressure (hpa) Height (km) Fingerprinting with temperature changes in Earth s atmosphere Model Changes: CO 2 + Sulfate Aerosols + Stratospheric Ozone N 45N 30N 15N 0 15S 30S 45S 60S 2 50 Observed Changes N 45N 30N 15N 0 15S 30S 45S 60S 2 Santer et al., Nature (1996) Temperature changes in o C 12

13 Fingerprint research has made important contributions to the conclusions of IPCC assessments The balance of evidence suggests a discernible human influence on global climate There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities Most of the observed increase in globally averaged temperatures since the mid-20 th century is very likely* due to the observed increase in anthropogenic greenhouse gas concentrations 13

14 We have now identified human fingerprints in TEMPERATURE FIELDS 1. Global-scale surface temperatures 2. Regional-scale surface temperatures 3. Vertical profiles of atmospheric temperature 4. Global ocean heat content 5. MSU stratospheric and tropospheric temperatures 6. The height of the tropopause 7. Vertical structure of upper-ocean temperatures 8. SSTs in hurricane formation regions 9. Arctic and Antarctic temperatures 14

15 We ve moved beyond temperature only fingerprint detection studies ATMOSPHERIC CIRCULATION, SEA-ICE, AND THE HYDROLOGICAL CYCLE 1. Sea-level pressure 2. Continental-scale runoff 3. Atmospheric water vapor over oceans 4. Surface specific humidity 5. Zonal-mean precipitation 6. Hydrologically-relevant climate variables in the western U.S. 7. Arctic sea-ice extent 15

16 Structure of talk Climate change 101 A brief review of climate fingerprinting Update on recent changes in greenhouse gases Update on recent changes in climate (and projections of future changes) Update on fingerprint research Conclusions 16

17 Changes in atmospheric concentrations of greenhouse gases over the past 30+ years 17

18 Recent changes in atmospheric CO 2 and CH 4 concentrations Researchers measured an additional 16.2 billion tons of carbon dioxide and 12.2 million tons of methane in the atmosphere at the end of December 2008 This increase occurred despite the global economic downturn, with its decrease in a wide range of activities that depend on fossil fuel use 18

19 5 Recent emissions Emissions of greenhouse gases are growing more 0 rapidly than anticipated CO 2 Emissions (GtC y -1 ) Actual emissions: CDIAC Actual emissions: EIA 450ppm stabilisation 650ppm stabilisation A1FI A1B A1T A2 B1 B Raupach et al., PNAS (2007)

20 Will there be abrupt changes in atmospheric concentrations of methane? CCSP Report 3.4, (December 2008) It is possible that large amounts of methane present in solid form (methane hydrate) in ocean sediments may become unstable as the planet continues to warm Warming can destabilize methane hydrate, forming free gas that may be ultimately released to the atmosphere A catastrophic release of methane to the atmosphere in the next century appears very unlikely It is very likely, however, that human-caused climate change will accelerate the pace of persistent emissions of methane from both hydrate sources and thawing out of organic matter in permafrost 20

21 Structure of talk Climate change 101 A brief review of climate fingerprinting Update on recent changes in greenhouse gases Update on recent changes in climate (and projections of future changes) Update on fingerprint research Conclusions 21

22 Latest information on global mean temperature changes 22

23 Latest information on global mean temperature changes 23

24 Has the Earth stopped warming? A climate simulation in a world facing business as usual increases in greenhouse gases still shows lots of periods with cool fluctuations 24

25 Earth s temperature has increased over the last 30 years, despite no overall increase in the Sun s energy output U.S. Climate Change Science Program (CCSP) Unified Synthesis Product (2009) 25

26 Estimates of historical and future sea-level rise from the IPCC Fourth Assessment Report Range for A1B: 0.21 to 0.48 m Total 20 th century rise: 0.17 meters FAQ 5.1, Figure 1 26

27 Contributions of ice-sheet dynamics to sea-level rise are highly uncertain CCSP Report 3.4, (December 2008) An abrupt change in sea level from the melting of land ice is possible Predictions are highly uncertain Recent rapid changes at the edges of the Greenland and West Antarctic ice sheets show acceleration of flow and thinning Glacier acceleration may be due to such processes as: Enhanced surface meltwater production penetrating to the glacier bed, lubricating glacier flow Ice shelf removal Glacier ungrounding Interaction of warm ocean waters with the periphery of large ice sheets 27

28 The impacts of ice sheet dynamics on sea-level rise are highly uncertain U.S. Climate Change Science Program (CCSP) Unified Synthesis Product (2009) 28

29 Latest information on Arctic sea ice changes Monthly March ice extent for 1979 to 2009 shows a decline of 2.7% per decade Arctic sea ice is becoming thinner than average 29

30 Increasing atmospheric CO 2 concentrations lead to increasing acidification of the ocean Dissolved CO 2 forms a weak acid European Station for Time Series in the Ocean (29 N, 15 W) ph decreases as dissolved CO 2 increases Direct observations of ph over last two decades show ph decreases of about 0.02 units per decade Projections based on SRES scenarios give reductions in average global surface ph of 0.14 to 0.35 units over the 21 st century Bad news for marine organisms which use aragonite and calcite to build shells Hawaii Ocean Time Series (23 N, 158 W) Bermuda Atlantic Time Series Study (32 N, 64 W) IPCC Fourth Assessment Report (2007) Figure

31 Will there be an abrupt change in the Atlantic Conveyor Belt circulation? CCSP Report 3.4, (December 2008) The Atlantic Conveyor Belt circulation transports a substantial amount of heat from the Tropics and Southern Hemisphere toward the North Atlantic Changes in this ocean circulation could have a profound impact on many aspects of the global climate system As greenhouse gas levels increase, it is very likely that the strength of the Atlantic Conveyor Belt will decrease by approximately 25-30% over the course of the 21 st century It is very unlikely that this circulation will undergo a collapse or an abrupt transition to a weakened state 31

32 Structure of talk Climate change 101 A brief review of climate fingerprinting Update on recent changes in greenhouse gases Update on recent changes in climate (and projections of future changes) Update on fingerprint research Conclusions 32

33 Key scientific issues in fingerprint research (I) 1. Most fingerprint work has focused on global-scale changes in individual, primary climate variables Can we identify human effects on climate at continental to regional scales? Can we identify human fingerprints in variables of direct relevance to climatechange impacts? (e.g., timing of stream flow, snowpack depth) Can we attribute shifts in the distributions of plant and animal species to human influences? 33

34 Key scientific issues in fingerprint research (II) 2. We now live in a multi-model world, yet most fingerprint studies to date have been performed with individual models Is it a model democracy ( One model, one vote? ) Or should we pay more attention to models that do a better job in capturing aspects of present-day climate that we care about? 34

35 Key scientific issues in fingerprint research (II) 2. We now live in a multi-model world, yet most fingerprint studies to date have been performed with individual models Is it a model democracy ( One model, one vote? ) Or should we pay more attention to models that do a better job in capturing aspects of present-day climate that we care about? 35

36 Key scientific issues in fingerprint research (III) 3. We cannot confidently attribute any specific extreme event to humaninduced climate change But can we make informed scientific statements about the influence of human activities on the likelihood of extreme events? 36

37 Estimated likelihood Evaluation Fractional Attributable Risk Risk of European heat wave exceeding 1.6 C threshold with and without human influence (Stott, Stone, and Allen, Nature, 2004) Average simulation omitting human influence Average model simulation with combined human and natural effects Number of occurrences per 1,000 years 37

38 Estimated likelihood Evaluating Fractional Attributable Risk Risk of European heat wave exceeding 1.6 C threshold with and without human influence (Stott, Stone, and Allen, Nature, 2004) Average simulation omitting human influence 0.4 Average model simulation with combined human and natural effects Number of occurrences per 1,000 years Can we do this type of analysis with other extreme events? 38

39 Conclusions We have identified human fingerprints in a number of different aspects of the climate system We have moved beyond temperature only detection and attribution Criticisms leveled at IPCC Second Assessment Report ( you are only looking at surface temperature changes ) are no longer valid The climate system is telling us a physically- and internally-consistent story The story s message: Natural causes alone cannot explain the observed changes Many scientists at dozens of universities and research institutions around the world have helped to tell this story 39

40 Addendum: EPA proposes regulating greenhouse gases (Washington Post, April 17, 2009) The Environmental Protection Agency issued a proposal today finding greenhouse gas emissions pose a danger to the public's health and welfare, a determination that could trigger a series of sweeping regulations affecting everything from vehicles to coal-fired power plants. In a statement issued at noon, EPA administrator Lisa P. Jackson said, This finding confirms that greenhouse gas pollution is a serious problem now and for future generations. She added, This pollution problem has a solution one that will create millions of green jobs and end our country s dependence on foreign oil. The finding identifies six gases carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride as contributing to global warming. The move, coming almost exactly two years after the Supreme Court ordered the agency to examine whether emissions linked to climate change should be curbed under the Clean Air Act, marks a major shift in the federal government s approach to global warming. 40

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