Key findings of the IPCC WG I Fifth Assessment Report

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1 Key findings of the IPCC WG I Fifth Assessment Report Courtesy: Julie Arblaster Lead Author, Chapter 12: Long-term Climate Change with thanks to AR5 authors for their contributions Yann Arthus-Bertrand / Altitude What is happening in the climate system? What are the risks? What can be done? Courtesy: Jean-Pascal van Ypersele, IPCC Vice-Chair 1

2 WG I (Physical science basis): 209 lead authors, 2014 pages, review comments WG II (Impacts, Adaptation and Vulnerability): 243 lead authors, 2500 pages, review comment WG III (Mitigation of Climate Change): 235 coordinating and lead authors, 2000 pages, review comments Courtesy: Jean-Pascal van Ypersele, IPCC Vice-Chair Background to the IPCC and 5 th Assessment Report Working Group I of the AR5 has 259 authors from 39 countries Fourteen chapters: some timescale based, others phenomenological with final plenary approval of the Summary for Policymakers on September 27, 2013 The IPCC authors assess the current understanding of climate variability and change, based primarily on the peer-reviewed literature (> 9000 articles cited) The reports are an assessment, not a review and policy-relevant, not policy-prescriptive Transparent multiple rounds of review, with each review comment (~1500 per chapter) responded to individually First Order Draft 21,400 comments 659 experts Second Order Draft 31,422 comments 800 experts 26 governments 2

3 Headlines of the IPCC WGI 5 th Assessment Report => Warming is unequivocal. Many observed changes are unprecedented on timescales of decades or millennia => Human influence on climate is clear => Climate will continue to change in future => Limiting future climate change will require substantial and sustained reductions in emissions New findings since the Fourth Assessment Report Increased certainty of a human influence on climate Improved observations & models and increased understanding of many components of the climate system New emission scenarios and projections of climate change beyond 2100 to 2300 Sea level rise projections include ice-sheet dynamical changes Estimates of the total allowable global emissions in order to limit temperature rise to e.g. 2 C above pre-industrial 3

4 Global mean surface temperatures increased by 0.89ºC between 1901 and 2012 Globally averaged surface temperatures IPCC (2013) Figure SPM.1 Almost the entire globe warmed between 1901 and 2012 C over period IPCC (2013) Figure SPM.1 4

5 Arctic summer sea ice extent has decreased IPCC (2013) Figure SPM.3 The oceans have warmed, accounting for more than 90% of the extra energy stored by the earth system since 1971 IPCC (2013) Figure SPM.3 5

6 Global mean sea level increased by 0.19 m between 1901 and : 1.7 mm/yr : 3.2 mm/yr IPCC (2013) Figure SPM.3 Atmospheric carbon dioxide concentrations have increased by 40% since pre-industrial times, to levels unprecedented in at least 800,000 years IPCC (2013) Figure SPM.4 6

7 Multiple lines of robust and compelling evidence support the conclusion that many aspects of the climate system have changed Human influence on climate is clear It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20 th century Increased certainty since the Fourth Assessment Report from a combination of improved observations, models and scientific understanding IPCC (2013) Figure SPM.6 7

8 Global warming continues despite slow-down in surface temperature rise over trends over short records are very sensitive to start and end dates and natural climate variability IPCC attributes the slow-down in roughly equal measure to: reduction in energy reaching the surface due to a downward phase of the 11-year solar cycle and shading by aerosols produced by volcanic eruptions (low confidence) internal variability including a possible redistribution of heat within the ocean (medium confidence) How will the climate change in the future? RCPs Future climate depends on: inherent variability social & economic choices response of the Earth system use a scenario approach where a variety of potential pathways are examined IPCC (2013) Figure TS.15 Representative Concentration Pathways (RCPs) encompass a range of plausible futures use comprehensive climate models as they are the best tools available for projections 8

9 Distinction in warming between scenario changes with time Global temperatures are likely to exceed 1.5 C for all RCPs except RCP2.6 by the end of IPCC the 21 (2013) st C Figure and likely SPM.7 to exceed 2 C for RCP6.0 and RCP8.5 How large is the projected change in surface temperature compared with internal variability? IPCC (2013) Figure SPM.8 Box 12.1: Methods to Quantify Model Agreement in Maps Stippling indicates regions with large changes and high model agreement Hatching indicates regions with small changes or low model agreement 9

10 Climate extremes: more hot and fewer cold extremes IPCC (2013) Table SPM.1 More hot and fewer cold days and nights as global temperatures increase IPCC (2013) Figure

11 The contrast between wet and dry regions and wet and dry seasons will increase* *with some regional exceptions RCP2.6 RCP8.5 Stippling: changes are large compared with internal variability (greater than two standard deviations of internal variability), and at least 90% of models agree on sign of change IPCC (2013) Figure SPM.8 Wet extremes over most mid-latitudes land masses and wet tropics will very likely become more intense and more frequent IPCC (2013) Figure

12 The rate of sea level rise is very likely to increase IPCC (2013) Figure SPM.9 12

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15 Further Information Yann Arthus-Bertrand / Altitude 15