whatclimate researchers said and what they never said ... · biarritz, 18 october 2011 what climate...

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


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


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)


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


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?


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


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.


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


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


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


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.


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.

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


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


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)


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


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

whatclimate researchers said and what they never said ... · biarritz, 18 october 2011 what climate...

Documents