Climate sciences, physical science basis

Valérie Masson-DelmotteLaboratoire des Sciences du Climat et de l’Environnement
Co-présidente du groupe de travail I du GIECvalmasdel

A tremendous scientific endeavour

Fluid physics
Thermodynamics
Radiative transfers

Antiquity

MiddleAge

17th Century
Meteorologicalinstruments A vast scientific community Curiosity-driven research Societal and policy relevance

19th Century
Networks
Ice ages
Greenhouse effect

Quantitative paleoclimate
Supercomputers
Satellites

Late 20th Century
Key concepts
Climate modelling
Statistical analyses

Climate models

Physicalprinciples

WeatherforecastR. Knutti, ETH ZürichClimatepatterns

Recent trends

Past climates

ProcessesRobustness

Atmospheric composition is deeply modified
by human activities
Dioxyde de carbone (CO2)

40% above pre industrial levels

Méthane (CH4)2,3 times pre-industrial levels

Net effect of human activities : an imbalance of the Earth’s energy budget
In 2011 + 2,3 W/m2

Nos activités agissent
sur le bilan d’énergie de la Terre
imbalance

Infra-red radiation

ice

ocean

airsoils

3%
3%
93%

Climate is changing due tothe Earth’s energy imbalance

WCRP, 20171%

Nos activités agissent
sur le bilan d’énergie de la Terredéséquilibrerayonnement infra-rouge

glace

océan

airsols3%
3%
93%

Ocean heat content (1022 J)

The oceanaccumulates
most of theextra heatwww.nodc.noaa.gov
Année

1%

Consequences of the Earth’s energy
imbalance
iimbalanceextrêmes

air temperaturehumidity

ice sheets

seatemperatureflood

Sea levelsea iceheatWCRP, 2017

submersion

droughtSnow,glaciers

Role of natural and human factors inobserved warming
Global warming compared to 1850-1879 (°C)
Monthly observations (HadCRUT4)
All factors
Human activities (5-95%)
Solar and volcanic activity (5-95%)

From knowledge production …
20000

Number of peer-review papers with« climate change » keyword
15000

10000

5000

0
1970

1975

1980

1985

1990

1995

2000

2005

2010

2015

to the assessment of the state of knowledge
 International climate research is coordinated by the World
Climate Research Programme (WCRP), related to WMO, UNEPand IOC
 The IPCC is a scientific body under WMO and UNEP
 IPCC assessment reports are key sources of scientificinformation for the United Nation Framework Convention on
Climate Change (UNFCCC)

 in 2018 : 30 years of IPCC assessments

Report preparation steps
1. Plenary
decision toprepare areportPublications
cut-off submission date

Scoping

Outline approval

Ad@CutSecondOrder Draft+ draft SPM

Expert andgovernment
review

Publications
cut-off acceptance date

Nominations of authors

ExpertreviewFirstOrderDraft

Selection of authors

Cut

Cut
Final
chapters& SPM forgov.
review

SPM = Summary for Policy Makers

Goverment
review ofSPM

Final
SPM
draft

Cut Plenary
approval

12. Report
Publication!

Sixth assessment cycle of the IPCCMay 2019
Emission
inventories

Oct. 2018Sept. 2019

Globalwarming of
1.5 oC

Oceansand cryosphereTalanoa
dialogue
UNFCCC

Land

Aug. 2019

April 2021

October 2021

April 2022

The PhysicalScience Basis

Climate Change
Impacts,
Adaptation andVulnerability

The Synthesis
ReportMitigationof
Climate Change
July 2021

Global stocktake
2023
UNFCCCHuman activities have caused around 1°Cof global warming
Warming above 1850-1900 (°C)

Monthly observations
Estimation ofhuman inducedwarming
Projections of stabilized warming if CO2 reach net
zéro around 2040 or 2055 and if the effect of othernon CO2 factors is stabilised after 2030 or is reduced
after 2030

IPCC, 2018 (www.ipcc.ch/report/sr15)

1.5°C warmer world
Change inannualmean
temperature

Change inannual mean
precipitation

26 CMIP5 models
hatching : 66% coherency

IPCC, 2018 (www.ipcc.ch/report/sr15)

2°C warmer world

1.5°C warmer world

Most intense
rainfall

IPCC, 2018 (www.ipcc.ch/report/sr15)

2°C warmer world

1.5°C warmer world

Number of very hotdays

Temperature ofhottest days

Temperature ofcoldest nights

IPCC, 2018 (www.ipcc.ch/report/sr15)

2°C warmer worldImpacts and risks for different natural, managed and human systems

Level of warming compared to 1850-1900 (°C)

Impacts / risques
Very highHighmoderate
undetectable
IPCC, 2018 (www.ipcc.ch/report/sr15)

Trajectories of CO2 emissions which could stabilie global warming at 1,5°C with andwithout overshootAnnual emissions (billon tons CO2)

data.ene.iiasa.ac.at/iamc-1.5c-explorer/

net zero:
IPCC, 2018 (www.ipcc.ch/report/sr15)

Emergence and intensity of regional climate change hot spots
Arctic summer sea-ice
 L maintained; 50% or higher risk to be ice free; VL to be ice free
 Habitat (polar bear, whales, seals, sea birds) : losses; losses; critical losses Arctic fisheries : benefits; benefits; benefits

Warming of 1.5°C or
less
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidenceEmergence and intensity of regional climate change hot spots
Arctic land regions
 Cold extreme: warm up to 4.5°C (HC); warm up to 8°C (HC); VL drastic warming Tundra : L biome shifts; L more shifts; drastic biome shift possible (LC) Permafrost : L 17-44% reduction; L larger (28-53%); potential for collapse (LC) Boreal forest : increased mortality at S. boundary (MC); further (MC); potential dieback (LC)

Warming of 1.5°C orless
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidenceEmergence and intensity of regional climate change hot spots

Alpine regions
 Biomes : L severe shift; L even more severe; L critical

Warming of 1.5°C or
less
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidenceEmergence and intensity of regional climate change hot spots

Mediterranean Extreme drought: increase probability(MC); robust increase(MC); robust and large increase(MC) Runoff decrease: about 9% (MC); about 17% (MC); substantial reductions (MC) Water deficit: risk (MC); higher risks (MC); very high risks (MC)Warming of 1.5°C orless
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidenceEmergence and intensity of regional climate change hot spotsTropics
 # hot days and nights, heatwaves: increases (HC); largest increase; oppressive, VL health impact
 Livestock heat stress : increased; onset of persistent (MC); L persistent Crop yields: risks; extensive risks (W. Africa, SE Asia, S. America); VL substantial reductions
 Rainforests : reduced biomass; larger reductions; reduced extent, potential forest dieback (MC)Warming of 1.5°C orless
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidenceEmergence and intensity of regional climate change hot spots
L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidence

Warming of 1.5°C or
less
Warming of 1.5ºC-2°C
Warming > 2°C

Southeast Asia  flooding related to sea-level rise: risks; higher risks (MC); substantial increases in risk
 Asian monsoon : LC; LC; L increase in precipitation intensity
 Heavy precipitation: increase; stronger increase (MC); substantial increase Crop yield reductions: -; one third decline in per capita (MC); substantial reduction

Emergence and intensity of regional climate change hot spots
Warming of 1.5°C orless
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidenceWest African and the Sahel Monsoon : uncertain ; uncertain ; strengthening (LC) Hot nights, longer, more frequent heat waves: L ; L further ; VL substantial   in maize and sorghum production: L, about 40%  suitable area; L larger ;major regional food insecurities (MC) Undernutrition risks : increased; higher; highEmergence and intensity of regional climate change hot spots
Warming of 1.5°C or
less
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidence

Southern Africa
 Water availability: reductions (MC); larger reductions (MC); large reductions (MC)
 # of hot nights and  heat waves : increases (HC); further increase (HC); drastic increase (HC) Increased mortality from heat-waves: high risks; higher risks (HC);sustantial impact on health and mortality (HC) Undernutrition / dryland agriculture and livestock: high risk; higher risk (HC); very high risks

Emergence and intensity of regional climate change hot spots
Warming of 1.5°C orless
Warming of 1.5ºC-2°C
Warming > 2°C

L, likely
VL, very likely
LC, low confidenceMC, medium confidenceHC, high confidence

Small islands: Inundation risk : land exposed; tens of thousands displaced ; substantial, widespread impacts
 Coastal flooding: risks; high risks ; substantial and widespread impacts
 Fresh water stress : increased; projected aridity; substantial and widespread impacts
 # of warm days : increase; further increase (70 warm days/year), persistent heat stress incattle ; persistent heat stress Loss of coral reefs: 70-90%; most coral reefs ; loss of most coral reefs (VL)