Download 2°C - Louis Bachelier

What do we know about
medium term climate change?
Valérie Masson-Delmotte
The climate system
External perturbations
Interactions, feedbacks
WCRP
Internal variability
Response to perturbations
Anthropogenic CO2 emissions
Atmospheric
CO2
Concentration
(ppm)
Atmosphere
in 1870
Global Carbon Project, 2016
Atmosphere
in 2015
Atmospheric composition
ppm
ppb
NOAA, 2016
ppb
ppt
Radiative perturbation
Harold et al, Nature Climate Change, 2016 based on IPCC 2013
Components of change
in radiative forcing since 1750
?
Adapted from IPCC 2013 (shrinkthatfootprint.com)
Nos activités agissent
sur le bilan d’énergie de la Terre
von Schuckmann, K. et al, Nature Climate Change, 2016
Change in Earth’s surface temperature
WMO 2016
Human influence
Surface warming 1950-2010
Observed
Greenhouse gas
Human influence
Anthropogenic aerosols
Solar and volcanic activity
Internal variability
IPCC 2013
Change in intensity and frequency
of extreme events
Hansen et al PNAS, 2012
State of knowledge : human influence on extreme events
NAS Report, Attribution of extreme
weather events, 2016

Capabilities of climate models

Available observations

Physical mechanisms
Evaluation of climate models
Reto Knutti
Comparing projections after 2005 with
observations
Difference between weather forecast,
predictability, and projections
IPCC 2013
Projections explore climate response to
different emission pathways
Greenhouse gas emission pathways
GIEC 2013
Projections explore climate response to
different emission pathways
Greenhouse gas emission pathways
Radiative forcing (W/m2)
Projections explore climate response to
different emission pathways
Greenhouse gas emission pathways
Radiative forcing (W/m2)
Climate response (°C)
Projections explore climate response to
different emission pathways
Greenhouse gas emission pathways
Additional risks
Radiative forcing (W/m2)
Climate response (°C)
Cumulative emissions of carbon dioxide largely
determine global mean surface warming
2°C target
Amount
Remaining
Amount Used
1870-2011
IPCC 2013
Regional aspects of surface warming
2°C
1.5°C
4°C
°C
Number of very
hot days
Global warming (°C)
Knutti et al, Nat. Geo., 2015
Regional aspects of precipitation change
1.5°C
2°C
4°C
% precipitation
change
Water cycle change :
• for 50% of world’s population at +2°C
• for 40% of land surface at +3°C
Sedlacek and Knutti, 2014; Knutti et al, Nat. Geo., 2015
Potential irreversible change :
marine ecosystems
Ocean acidification (pH)
Arctic sea ice extent
in September (millions of km2)
Cumulative CO2 emissions since 1850 (Gt CO2)
3 m2 loss per ton CO2 emitted
IPCC, 2013; Notz and Stroeve, Science, 2016
Potential irreversible consequences :
sea level
by 2100
over thousand years
• Recent findings suggest risk of destabilisation of marine sectors of Antarctica
for 3°C warming or more, strongly enhancing sea level risks on time scales of 50 – 500 years
IPCC, 2013; Pollard and de Conto, Nature, 2016
Changing risks for 1.5 – 2°C warming
Schleussner et al, ESSD, 2016
Risks of abrupt change
Catalogue in projections
Intensity of global warming (°C)
Drijfhout et al, PNAS, 2015
Mitigation pathways to reduce risks
NDC
Rogelj et al, Nature, 2016
Future climate assessments
www.ipcc.ch
AR6 cycle Special Reports on
Impacts of global warming of 1.5 ºC above pre-industrial levels and
related global greenhouse gas emission pathways by 2018
Climate change and oceans and the cryosphere
Climate change, desertification, land degradation, sustainable
land management, food security, and greenhouse gas fluxes in
terrestrial ecosystems
Outline of special report
Global warming of 1.5 oC
Chapter 1: Framing and context
Publications
Submitted by October 2017
Accepted by April 2018
Chapter 2: Mitigation pathways compatible with 1.5°C in the context of
sustainable development
Chapter 3: Impacts of 1.5°C global warming on natural and human
systems
Chapter 4: Strengthening and implementing the global response to the
threat of climate change
Chapter 5: Sustainable development, poverty eradication and reducing
inequalities
Notes from scoping meeting
Ocean and cryosphere
Chapter 1: Framing and context
Publications
Submitted by October 2018
Accepted by April 2019
Chapter 2: High mountain areas
Chapter 3: Polar regions
Chapter 4: Implications of sea level rise for coasts and communities
Chapter 5: Changing ocean, marine ecosystems, and dependent
communities
Chapter 6: Extremes, abrupt change and managing risks
Box : low lying islands and coasts
In preparation
AR6 Main Report
AR6
Expected to be released in three working group contributions in
2020/2021 and a Synthesis Report in 2022
Methodology Report update
TFI
Methodology Report on National Greenhouse Gas Inventories
by 2019
Cities
Attention on cities in AR6 including a conference in Jan. 2018 and
special report on cities in AR7
Timeline
Sept 2018
Fall 2019
Global
warming of
1.5 oC
Oceans
and cryosphere
Facilitative
dialogue
UNFCCC
Land Use
Fall 2019
April 2021
October 2021
April 2022
The Physical
Science Basis
Climate Change
Impacts,
Adaptation and
Vulnerability
The Synthesis
Report
Mitigation
of
Climate Change
July 2021
Global
Stocktake 2023
UNFCCC
IPCC assessments
 Rigorous
 Robust
 Transparent
 Comprehensive
World CO2emissions
(Gt per year)
Chine
USA
UE-28
Inde
Global Carbon Project
Observed Concentrations Compared to IPCC Projections