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Biarritz, 18 October 2011

What climate researchers said and what they NEVER said. State of the climate in 2011. Christophe Cassou (CNRS-Cerfacs). Costal ecosystems vulnerability to global change and extreme events. Biarritz, 18 October 2011. Introduction.

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Biarritz, 18 October 2011

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  1. What climate researchers said and what they NEVER said State of the climate in 2011 Christophe Cassou (CNRS-Cerfacs) Costal ecosystems vulnerability to global change and extreme events Biarritz, 18 October 2011

  2. Introduction Climate people: a research community under constant attacks. Easy target… Why? 1. Climate observations are spatially very sparse and temporally very limited for most of climate variables: i. Is the global mean temperature a relevant indicator ? ii. Can current trends be “detected” (i.e. not compatible to natural variability)? iii. Can current changes be attributed to human activities? 2. Climate predictability is complex because of the presence of several sources that operate at different spatio-temporal scales. i. Confusion between weather forecast and climate forecast (probabilistic thinking is difficult, isn’t it?) ii. Confusion between climate projections (last IPCC report in 2007) and climate prediction iii. Ignorance about the tools (modeling) and their limits, used for forecast and detection/attribution issues 3. Uncertainties is inherent to climate by construction i. uncertainties is treated as a synonym for ignorance ii. uncertainties triggers non-rational reactions driven by psychological reflexes Climate issues go far beyond the sole scientific questions Costal ecosystems vulnerability to global change and extreme events

  3. Atmospheric composition Relationship between CO2, CH4 and temperature 2005 Source: Delmotte et al., 2007 Inter-glacial period CO2 Temp. CH4 1. Is the current atmospheric composition atypical with respect to the last million of years, i.e. is it detectable? 2. If so, can it be attributed to anthropogenic activities? Costal ecosystems vulnerability to global change and extreme events

  4. Anthropogenic source for GHG increase Extremely rapid rise since the beginning of industrial revolution What chemists say: CO2 produced from fossil fuel burning and deforestation has a different isotopic composition from« natural »CO2 in the atmosphere: We observe a decrease 14C/12C and 13C/12C ratio and a concommitent decline of O2 Recent changes in atmospheric composition are detectable and attributable to human activities Costal ecosystems vulnerability to global change and extreme events Source: IPCC AR4

  5. Accumulation : 3,3 billions of tons per year Accumulation : 0 Perturbation of the carbon cycle Echanges océans - atmosphère Echanges continents - atmosphère Emission 5,5 1,6 Absorption 1,8 2,0 Billions of tons per year The naturalcarbon cycle Acidification of the ocean The anthropogenic -perturbedcarbon cycle Perturbation of the radiative budget at the earth surface (increased greenhouse effect) Costal ecosystems vulnerability to global change and extreme events

  6. Global temperature change from 1880 to 2010 Reference period = [1960-1990] Source: GISS dataset Presence of several timescales of variability: i. A pronounced warming trend since the 1970’s ii. Evidence for decadal modulations iii. Significant interannual variability Costal ecosystems vulnerability to global change and extreme events

  7. RETROACTION RETROACTION EXTERNAL PERTURBATION Why climate varies : the climate system NATURAL Anthropogenic Greenhouse gases + + + INTERNALCOUPLING Land use PHYSICS DYNAMICS CHEMISTRY

  8. Total (2000)= ~2 W/m2 Radiative forcing change from 1850 to 2005 Is the trend compatible with internal variability, i.e. not detectable? If not, can it be attributed to one or more external forcing? Costal ecosystems vulnerability to global change and extreme events

  9. Spatial resolution: Constraint on the physical processes Necessary representation of physical entities of spatial scale smaller than the grid point (parameterization) Temporal resolution: Constraint on the physical processes What is a climate model? Source: IPCC AR4 Spatial discretization (grid) Time stepping Costal ecosystems vulnerability to global change and extreme events

  10. From the 1st IPCC report to the 4th Costal ecosystems vulnerability to global change and extreme events Source: IPCC AR4

  11. Detection CSTE (1850) CSTE (1850) Observation Global temperature (CNRM-CM5) Internal Year of model integration The observed trend is not compatible with the climate internal variability

  12. Attribution (1) CSTE (1850) Observed [1850-2010] CSTE (1850) Observed [1950-2010] External External Global temperature (CNRM-CM5) Internal Year of model integration The observed trend is compatible with a response to external forcings

  13. Attribution (2) CSTE (1850) Observed [1850-2010] CSTE (1850) Observed [1950-2010] CSTE (1850) Natural External All forcings included except GHGs All forcings included Observations IPCC models Source: IPCC AR4 Costal ecosystems vulnerability to global change and extreme events

  14. The 4th Assessment Report (AR4 – 2007) The warming of the climate system is unambiguous because there are numerous evidence from the observations that global temperature both in the ocean and atmosphere is increasing, that sea ice, snow cover and icecap are massively declining and that sea-level is significantly rising.  Most of the global temperature warming since the mid-XXth century is very likely associated with the observed increase of greenhouse gases concentration due to human activities.  Discernable proofs for anthropologic imprints can be now found in many climate indices: subsurface ocean warming, mean continental temperature, extreme temperatures, wind fields… i.e. well beyond the supposedly contested “global mean temperature” as indicator. Costal ecosystems vulnerability to global change and extreme events

  15. Internal variability : El Nino 1998 Sea surface temperature 2008 El NINO LA NINA Most of the interannual variability at global timescale is associated with El Nino /La Nina alternation (ENSO) Costal ecosystems vulnerability to global change and extreme events

  16. Interannual variability 2003 Mean temperature over France 2010 NAO- A large part of the interannual variability over Europe is linked to the North Atlantic Oscillation Costal ecosystems vulnerability to global change and extreme events

  17. Interannual variability 2010 : the warmest year, the wettest at global scale, but regional departures DO exist (Europe…)

  18. Observed decadal natural variability Presence of decadal fluctuations superimposed on a trend From Hurrell (2010) Costal ecosystems vulnerability to global change and extreme events

  19. Decadal internal variability : AMO AMO= Atlantic Multidecadal Oscillation Index: Oean temperature averaged over the entire North Atlantic Ocean Monthly index of the AMO (1860-2008) Warm North Atlantic Cold North Atlantic 1967 1902 1930 1995 http://www.cdc.noaa.gov/data/ AMO = a ~[40-70] yr oscillatory behavior and ~1995 is the last shift AMO explains a great part of decadal variability for a broad North Atlantic domain. Ex: strong impact on hurricane activity/ Sahel precip. Costal ecosystems vulnerability to global change and extreme events

  20. What climate researchers never said Climate researchers : 1. NEVER said that every new year will be warmer than the previous ones or that a cold wave could not occur anymore: because climate variability should be understood as a superimposition of external forced response + internal variability. The latter may temporally cancel out the anthropogenic effects, especially at regional scale. 2. NEVER tried to predict the phase of the internal decadal variability that modulates the trend, because SOFAR numerical simulations were designed to estimate the SOLE forced response : the copenhague hold-up. • honesty when the sole [1998-2008] period is only considered ? • and even if it was true, • SO WHAT ? Costal ecosystems vulnerability to global change and extreme events

  21. What climate researchers never said Climate researchers : 1. NEVER said that every new year will be warmer than the previous ones or that a cold wave could not occur anymore: because climate variability should be understood as a superimposition of external forced response + internal variability. The latter may temporally cancel out the anthropogenic effects, especially at regional scale. 2. NEVER tried to predict the phase of the internal decadal variability that modulates the trend, because SOFAR numerical simulations were designed to estimate the SOLE forced response : the copenhague hold-up. 3. NEVER attribute all the climates events to climate changes: that leads to misperception in general public : how to convey a message and who? INTERNAL vs EXTERNAL : Until when ? Use of climate scenarios Costal ecosystems vulnerability to global change and extreme events

  22. Climate scenarios CSTE (1850) Canonical 11yr- cycle CSTE (1850) Emission [1995-2100] Scenario pessimiste Scenario médian Scenario optimiste Projection Global temperature evolution IPCC models Observations The misuse of uncertainties (weight between the 3 contributions: internal variability, model deficiencies, scenario-type) A warming between ~1.4o and ~5o by the end of the century : acting now? Source: IPCC AR4

  23. Decadal forecast: a new but still fondamental research theme Global temperature change +1o +/- 0.5o Scenario pessimiste Scenario médian Scenario optimiste The uncertainties for the next two decades do not depend on the scenario The uncertainties mostly depend on low-frequency natural fluctuations and models: emergence of decadal forecast (ocean initialization) as opposed to scenarios (random initialization): A challenging issue tackled for the first time in the next IPCC report

  24. 27 27 26 26 25 25 24 24 23 23 22 22 21 21 20 20 19 19 18 18 17 17 16 16 +4oC 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 What does +4o mean for France? (1) Mean temperature observed in summer over France Temperature simulated by Meteo-France model (Scenario A1B) Costal ecosystems vulnerability to global change and extreme events

  25. 2003 L’été 2003 peut être considéré comme un avant gout de nos étés a la fin du siècle: Ce sera l’été « normal » (cad une fois sur deux de 2080), et un été froid pour 2100. +4oC What does +4o mean for France? (1) Anomaly 2003 = 3,7°C 40oC (weather) + 4oC (climate) Costal ecosystems vulnerability to global change and extreme events

  26. Observations Projection du GIEC AR4 IPCC models clearly underestimate the sea-ice declining Existence of nonlinear processes extremely hard to modelling Sea ice Source: http://www.copenhagendiagnosis.com Costal ecosystems vulnerability to global change and extreme events

  27. How are we doing today? Bilan 1993-2009 Fossil fluel emission of CO2 Hausse en mm par an Hausse observée par les satellites Total climat 3 mm/an Glaces 2 mm/an Antarct. + Groenland Source: http://www.copenhagendiagnosis.com Océan Sea level 1 mm/an Glaciers Eaux Terrestres Source: Cazenave and Llovel (2010)

  28. Thank you

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