What do we know about medium term climate change? Accord de Paris : ratifié par 115 parties sur 197, représentant 79% des rejets de gaz à effet de serre Entré en vigueur le 4 novembre dernier (1 mois après seuil de 55 pays et 55% des émissions) Valérie Masson-Delmotte

The climate system External perturbations Interactions, feedbacks Internal variability Response to perturbations WCRP

Anthropogenic CO2 emissions Atmospheric CO2 Concentration (ppm) Mettre à jour avec GCP 2016 Atmosphere in 1870 Atmosphere in 2015 Global Carbon Project, 2016

Atmospheric composition ppb ppm ppb ppt Mettre à jour avec données les plus récentes site NOAA NOAA, 2016

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 IPCC 2013 Observed 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 Capabilities of climate models Available observations Physical mechanisms NAS Report, Attribution of extreme weather events, 2016

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 Radiative forcing (W/m2) Additional risks Climate response (°C)

Cumulative emissions of carbon dioxide largely determine global mean surface warming 2°C target Amount Used 1870-2011 Amount Remaining IPCC 2013

Regional aspects of surface warming Number of very hot days Global warming (°C) Knutti et al, Nat. Geo., 2015

Regional aspects of 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 Arctic sea ice extent in September (millions of km2) Ocean acidification (pH) 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 Publications Submitted by October 2017 Accepted by April 2018 Chapter 1: Framing and context 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 Is it really feasible to hold global warming to 1.5°C?   In fact, the UNFCCC did not ask IPCC to answer this question. Under the Paris Agreement It asked IPCC to assess the impacts of 1.5°C warming and associated emission pathways. But the question is frequently asked by the media and at public events. It is a difficult question for IPCC to address because people can mean very different things by “feasibility”. The 1.5°C report will not answer the question directly but will unpack it in ways that are useful to policymakers. Feasibility can refer to compatibility with the basic laws of chemistry and physics, to the scale and speed of change required in light of infrastructure and investment capacity, to the economic costs, to the sustainability of the necessary climate responses and to the capacity for social change. The report will touch on all these issues.

Notes from scoping meeting Ocean and cryosphere Publications Submitted by October 2018 Accepted by April 2019 Chapter 1: Framing and context 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 Is it really feasible to hold global warming to 1.5°C?   In fact, the UNFCCC did not ask IPCC to answer this question. Under the Paris Agreement It asked IPCC to assess the impacts of 1.5°C warming and associated emission pathways. But the question is frequently asked by the media and at public events. It is a difficult question for IPCC to address because people can mean very different things by “feasibility”. The 1.5°C report will not answer the question directly but will unpack it in ways that are useful to policymakers. Feasibility can refer to compatibility with the basic laws of chemistry and physics, to the scale and speed of change required in light of infrastructure and investment capacity, to the economic costs, to the sustainability of the necessary climate responses and to the capacity for social change. The report will touch on all these issues.

In preparation AR6 Main Report Methodology Report update Cities Expected to be released in three working group contributions in 2020/2021 and a Synthesis Report in 2022 AR6 Methodology Report update TFI Methodology Report on National Greenhouse Gas Inventories by 2019 Conference call januarau 18. Cities Attention on cities in AR6 including a conference in Jan. 2018 and special report on cities in AR7

Timeline Sept 2018 April 2021 October 2021 Fall 2019 April 2022 Global warming of 1.5 oC Oceans and cryosphere The Physical Science Basis Climate Change Impacts, Adaptation and Vulnerability The Synthesis Report Facilitative dialogue UNFCCC Land Use Mitigation of Climate Change Global Stocktake 2023 UNFCCC We need you for this processes. Develop the scientific basis, review the daft, be Authors (CLA, LA, CA, RE). Apply. Dont be frustrated if not Selected. Many ways to contrubte. Fall 2019 July 2021

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