climate change : a global science...
TRANSCRIPT
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Climate change :
a global science update
Valérie Masson-Delmotte
@valmasdel
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• Introduction
• Current global warming in context
• Human influence on extreme events
• Implications of warming targets
• Sea level
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Antiquity Middle
Age
17th Century
Meteorological
instruments
19th Century
Networks
Ice ages
Greenhouse effect
Fluid physicsThermodynamicsRadiative transfers
Late 20th Century
Key concepts
Climate modelling
Statistical analyses
Quantitative paleoclimateSupercomputersSatellites
A vast scientific community
Curiosity-driven research
Societal and policy relevance
A tremendous scientific endeavour
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From knowledge production…
0
5000
10000
15000
20000
1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Number of peer-review papers with« climate change » keyword
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Climate projections : IPCC AR5
Emission pathways Radiative perturbation (W/m2)
Simulated climate response (°C)Assessing risks
carbon
clouds
sea level
extremes
regional
volcanoes
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Vo
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• Introduction
• Current global warming in context
• Human influence on extreme events
• Implications of warming targets
• Sea level
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Where do we stand now for global
mean temperature?
Z. Hausfather
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Where do we stand now with
respect to pre-industrial levels?
Hawkins et al, BAMS, 2017
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Where do we stand now with respect to
the current and last interglacial periods ?
Hansen et al, ESD, 2017
Current interglacial period (Holocene)Last interglacial period (Eemian)
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Where do we stand now with respect
to earlier climate projections?
Z. Hausfather
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What are the drivers of climate change?
Heat – trapping gases
Sunshade effect
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What are the cumulative contributions
to the carbon budget?
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What is the best estimate of human
influence on global warming?
IPCC, 2013
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• Introduction
• Current global warming in context
• Human influence on extreme events
• Implications of warming targets
• New developments for projections
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NAS, 2016
How are extreme events
affected by human influence?
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How are extreme events
affected by human influence?
Example of a heavy rainfall event : Seine and Loire river basins, May 29-31, 2016
3 day precipitation extremes in April-June : the probability of a 3-day spring extreme rainfall has increased by 80-90% due to human influence on the climate system
wwa.climatecentral.org
30-40% reduced common wheat yield due to the wet springSource : Agritel
WWA
Agritel
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How are extreme events
affected by human influence?
Recent major drought events :
California: rainfall deficit linked to natural variability, water stress enhanced by warming trend
Griffin et al, GRL, 2014 ; Williams et al, GRL 2015 ; Diffenbaugh et al, PNAS, 2015 ; Cheng et al.,2016, J Clim
Levant region: drought twice more likely due to human influence on drying and warming trends
Bergaoui et al., 2015, BAMS ; Cook et al, JGR, 2016, Kelley et al, PNAS, 2015
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How are extreme events
affected by human influence?
Arctic, autumn 2016
DMI
1958-2002
2016
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How are extreme events
affected by human influence?
Arctic, autumn 2016
2016
Highly unlikely event in a pre-industrial climate
In 2050, business as usual scenario : about one year out of two
Reference : 1979-2004Simulations with natural and all forcings (1901-2026) Reanalyses year by year since 1979
wwa.climatecentral.org
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• Introduction
• Current global warming in context
• Human influence on extreme events
• Implications of warming targets
• New developments for projections
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What are the implications of
1.5, 2°C warming or more?
Knutti et al, Nat. Geo., 2015
Hot days
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Schleussner et al, Nature Climate Change, 2016
What are the implications of 1.5 or 2°C
warming for potential impacts?
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Which projection methods
are fit for purpose?
Example of European Alps
European Alps summer precipitation : regional models simulate a robust increase in convective precipitation at high elevations
Giorgi et al, Nature Geoscience, 2016
Global climate models Regional climate models
Simulated summerprecipitation change
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What are the implications of 1.5 or 2°C
warming for potential impacts?
Screen & Williamson, NCC, 2017Notz and Stroeve, Science, 2016
Loss of 3 ± 0.3 m2 of September Arctic sea ice for each ton CO2 emitted
2 °C may not be sufficient to avoid the loss of summer Arctic sea ice
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What are the implications of climate
targets for cumulative CO2 emissions?
IPCC 2013; Global Carbon Project 2016
<2.0°C, >66%
Indicative range
450-1050 GtCO2
2100
GtCO2
800
GtCO2
20 years
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Rogelj et al, Nature, 2016
What are the emission trajectories
compatible with climate targets?
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How can the uncertainty on climate
sensitivity be reduced?
Schneider et al, Nature Climate Change, 2017
Emergent contraints :links between observable cloud properties, feedbacks, and climate sensitivity
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How can the uncertainty on land carbon
feedbacks be reduced?
Mystakidis et al, Global Change Biology, 2016
Emergent contraints :links between evapotranspirationand gross primary production
Multi-model spread in net biome productivityreduced by more than 30% by 2100
Doubled projected decline in land sink
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When do climate models produce
abrupt changes?
Drijfhout et al, PNAS, 2015
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• Introduction
• Current global warming in context
• Human influence on extreme events
• Implications of warming targets
• Sea level
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Why has sea level rise accelerated?
5%
25%
Ocean thermal expansion
Glaciers
Terrestrial water
Antarctica
Greenland
Chen et al, Nature Climate Change, 2017
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How much could ice sheets contribute
to sea level rise?
IPCC, 2013
Only the collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the likely range during the 21st century
Multi-millennial sea level rise
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How much could ice sheets contribute
to sea level rise?
DeConto and Pollard, Nature, 2016
Marine ice sheet instability Marine ice cliff instability Projected Antarcticcontribution to sea level rise
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To conclude
New knowledge is under development, from multiple lines of evidence : paleoclimate, observations, process studies, theory and numerical models
- to document and understand past and current changes- to evaluate model fit for purpose and confidence in projections- to develop regional climate information and near term predictions
Close interplay between developments in climate science and needsfor risk assessment, adaptation and mitigation solution options
Challenges to knowledge developments worldwide : long termobservation networks, satellite programs, computing resources, data distribution centers for climate model results, and human resources