whatclimate researchers said and what they never said ... · biarritz, 18 october 2011 what climate...
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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
Introduction
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 constructioni. uncertainties is treated as a synonym for ignoranceii. uncertainties triggers non-rational reactions driven by psychological reflexes
Climate people: a research community under constant attacks.Easy target… Why?
Climate issues go far beyond the sole scientific questions
Costal ecosystems vulnerability to global change and extreme events
Relationship between CO2, CH4 and temperature
Source: Delmotte et al., 2007
2005
Atmospheric composition
Inter-glacialperiod
1. Is the current atmospheric composition atypical with respect to thelast million of years, i.e. is it detectable?
2. If so, can it be attributed to anthropogenic activities?
CO2
Temp.
CH4
Costal ecosystems vulnerability to global change and extreme events
Anthropogenic source for GHG increase
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
Extremely rapid rise since the beginning of industrial revolution
Recent changes in atmospheric composition are detectable and attributable to human activities
Source: IPCC AR4 Costal ecosystems vulnerability to global change and extreme events
Perturbation of the carbon cycle
Echanges continents- atmosphère
Echanges océans- atmosphère
Accumulation : 0
Billions of tons per year
The naturalcarbon cycle
Emission5,5 1,6
Absorption1,8 2,0
Accumulation : 3,3 billions of tons per year
The anthropogenic -perturbed
carbon cycle
Acidification of the ocean
Perturbation of the radiativebudget at the earth surface(increased greenhouse effect)
Costal ecosystems vulnerability to global change and extreme events
Global temperature change from 1880 to 2010
Source: GISS dataset
Reference period = [1960-1990]
Presence of several timescales of variability:i. A pronounced warming trend since the 1970’sii. Evidence for decadal modulationsiii. Significant interannual variability
Costal ecosystems vulnerability to global change and extreme events
Why climate varies : the climate system
PHYSICS DYNAMICS CHEMISTRY
INTERNALCOUPLING
+
AnthropogenicGreenhouse gases
+Land use
+
NATURAL
EXTERNALPERTURBATION
RETROACTION RETROACTION
Radiative forcing change from 1850 to 2005
Total (2000)= ~2 W/m2
Is the trend compatible with internalvariability, i.e. not detectable?
If not, can it be attributed to one ormore external forcing?
Costal ecosystems vulnerability to global change and extreme events
What is a climate model?
Source: IPCC AR4
Spatial discretization (grid)
Time stepping
Spatial resolution:Constraint on the physical processes
Necessary representation ofphysical entities of spatial scalesmaller than the grid point(parameterization)
Temporal resolution:Constraint on the physical processes
Costal ecosystems vulnerability to global change and extreme events
From the 1st IPCC report to the 4th
Source: IPCC AR4 Costal ecosystems vulnerability to global change and extreme events
Detection
CSTE (1850)
CSTE (1850)
ObservationGlobal temperature (CNRM-CM5)
Year of model integration
Inte
rnal
The observed trend is notcompatible with the climate internal variability
Attribution (1)
Year of model integrationThe observed trend iscompatible with a response to external forcings
CSTE (1850)
CSTE (1850)
Observed [1950-2010]
Observed[1850-2010]
Global temperature (CNRM-CM5)
Inte
rnal
Attribution (2)
CSTE (1850)
All forcings included
IPCC models
Observations
Source: IPCC AR4Costal ecosystems vulnerability to global change and extreme events
CSTE (1850)
Observed[1850-2010]
Observed [1950-2010]
CSTE (1850)
All forcings includedexcept GHGs
The 4th Assessment Report (AR4 – 2007)
The warming of the climate system is unambiguous becausethere are numerous evidence from the observations that globaltemperature both in the ocean and atmosphere is increasing,that sea ice, snow cover and icecap are massively declining andthat sea-level is significantly rising.
Most of the global temperature warming since the mid-XXthcentury is very likely associated with the observed increase ofgreenhouse gases concentration due to human activities.
Discernable proofs for anthropologic imprints can be nowfound in many climate indices: subsurface ocean warming,mean continental temperature, extreme temperatures, windfields… i.e. well beyond the supposedly contested “globalmean temperature” as indicator.
Costal ecosystems vulnerability to global change and extreme events
Internal variability : El Nino
1998
2008
LA NINA
Most of the interannual variability at global timescale is associated with El Nino /La Nina alternation (ENSO)
El NINO
Sea surface temperature
Costal ecosystems vulnerability to global change and extreme events
Interannual variability
2010
2003
NAO-
A large part of the interannual variability over Europe is linked to the North Atlantic Oscillation
Mean temperature over France
Costal ecosystems vulnerability to global change and extreme events
Interannual variability
2010 : the warmest year, the wettest at global scale, but regional departures DO exist (Europe…)
Observed decadal natural variability
From Hurrell (2010)
Presence of decadal fluctuations superimposed on a trend
Costal ecosystems vulnerability to global change and extreme events
Decadal internal variability : AMO
AMO= Atlantic Multidecadal OscillationIndex: Oean temperature averaged over the entire North Atlantic Ocean
Warm NorthAtlantic
Monthly index of the AMO (1860-2008)
1902 1930 1967 1995
Cold NorthAtlantic
http://www.cdc.noaa.gov/data/
AMO = a ~[40-70] yr oscillatory behavior and ~1995 is the last shiftAMO 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
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.
Costal ecosystems vulnerability to global change and extreme events
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.
a. honesty when the sole [1998-2008] period is only considered ?
b. and even if it was true, SO WHAT ?
What climate researchers never said
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
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.
Climate scenarios
CSTE (1850)
CSTE (1850)
Emission [1995-2100]
Canonical 11yr- cycle Scenario pessimiste
Scenario médian
Scenario optimiste
A warming between ~1.4o
and ~5o by the end of the century : acting now?
The misuse of uncertainties (weight between the 3 contributions: internal variability, model deficiencies, scenario-type)
IPCC models
Observations
Source: IPCC AR4
Global temperature evolution
Decadal forecast: a new but still fondamental research theme
Global temperature change
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
+1o +/-0.5o
What does +4o mean for France? (1)
1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100161718192021222324252627
1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100161718192021222324252627
Mean temperature observed in summerover France
Temperature simulated by Meteo-France model(Scenario A1B)
+4oC
Costal ecosystems vulnerability to global change and extreme events
1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100161718192021222324252627
2003
1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100161718192021222324252627
Anomaly 2003 = 3,7°C
+4oC
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(climate)
40oC(weather)
What does +4o mean for France? (1)
Costal ecosystems vulnerability to global change and extreme events
Sea ice
Projection du GIEC AR4
Observations
IPCC models clearly underestimate thesea-ice declining
Existence of nonlinear processesextremely hard to modelling
Source: http://www.copenhagendiagnosis.com
Costal ecosystems vulnerability to global change and extreme events
How are we doing today?
Source: http://www.copenhagendiagnosis.com
Fossil fluel emission of CO2
Sea level
Glaciers
Antarct. +
Groenland
Eaux Terrestres
Océan
Total climat
1 mm/an
3 mm/an
2 mm/an
Hausse en mm par an
Glaces
Hausse observéepar les satellites
Bilan 1993-2009
Source: Cazenave and Llovel (2010)
Thank you