Climate change : a global science update Valrie Masson-Delmotte - - PowerPoint PPT Presentation

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Climate change : a global science update Valrie Masson-Delmotte - - PowerPoint PPT Presentation

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Climate change : a global science update Valrie Masson-Delmotte @valmasdel Introduction Current global warming in context Human influence on extreme events Implications of warming targets Sea level A tremendous scientific

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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 physics Thermodynamics Radiative transfers Late 20th Century Key concepts Climate modelling Statistical analyses Quantitative paleoclimate Supercomputers Satellites

 A vast scientific community  Curiosity-driven research  Societal and policy relevance

A tremendous scientific endeavour

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From knowledge production…

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 volcanoe s

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Von Schuckmann et al, Nature Climate Change, 2016

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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 spring

Source : 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 : 1979-2004 Simulations 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 summer precipitation change

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What are the implications of 1.5 or 2°C warming for potential impacts?

Screen & Williamson, NCC, 2017 Notz 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 evapotranspiration and gross primary production  Multi-model spread in net biome productivity reduced 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 Antarctic contribution 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 needs for risk assessment, adaptation and mitigation solution options  Challenges to knowledge developments worldwide : long term

  • bservation networks, satellite programs, computing resources, data

distribution centers for climate model results, and human resources