Key Findings of the IPCC WG1 Fifth Assessment Report


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Presentation given by Dr Julie Arblaster Senior Research Scientist at the Australian Bureau of Meteorology and Lead Author of the ‘Long-term Climate Change: Projections, Commitments and Irreversibility‘ chapter of Working Group I (WGI) contribution to the IPCC Fifth Assessment Report. Julie presented the findings and likely trends suggested by the future climate projections of her work.

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  • Virtually certain that there will be more hot and fewer cold extremes
  • Setting emissions to zero is implausible but indicates the multicentury commitment of climate change due to the long lifetime of CO2 in the atmosphereCO2 and global temperatures decline gradually persistent warming for centuries continuing at the level of warming reachedOcean heat content continues to rise for centuries and larger forcing indicates larger delays in reaching equilibrium e.g. for RCP8.5 ocean themal expansion has almost doubled compared to 2300
  • Key Findings of the IPCC WG1 Fifth Assessment Report

    1. 1. Key findings of the IPCC WG I Fifth Assessment Report Julie Arblaster Lead Author, Chapter 12: Long-term Climate Change with thanks to AR5 authors for their contributions © Yann Arthus-Bertrand / Altitude
    2. 2. Background to the IPCC and 5th 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) First Order Draft 21,400 comments 659 experts The reports are an assessment, not a review and policy-relevant, not policy-prescriptive Second Order Draft 31,422 comments 800 experts 26 governments Transparent – multiple rounds of review, with each review comment (~1500 per chapter) responded to individually and available once report is published
    3. 3. Headlines of the IPCC WGI 5th 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
    4. 4. 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
    5. 5. Global mean surface temperatures increased by 0.89ºC between 1901 and 2012 Globally averaged surface temperatures IPCC (2013) Figure SPM.1
    6. 6. Almost the entire globe warmed between 1901 and 2012 °C over period IPCC (2013) Figure SPM.1
    7. 7. Warming has occurred almost throughout Australia since 1910 Trend in Maximum T °C/10 yrs Trend in Minimum T °C/10 yrs
    8. 8. Arctic summer sea ice extent has decreased IPCC (2013) Figure SPM.3
    9. 9. 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
    10. 10. Global mean sea level increased by 0.19 m between 1901 and 2010. 1901-2010: 1.7 mm/yr 1993-2010: 3.2 mm/yr IPCC (2013) Figure SPM.3
    11. 11. 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
    12. 12. Multiple lines of robust and compelling evidence support the conclusion that many aspects of the climate system have changed
    13. 13. 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-20th century Increased certainty since the Fourth Assessment Report from a combination of improved observations, models and scientific understanding IPCC (2013) Figure SPM.6
    14. 14. Global warming continues despite slow-down in surface 1998 temperature rise over 1998-2012 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)
    15. 15. 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
    16. 16. Distinction in warming between scenario changes with time Global temperatures are likely to exceed 1.5°C for all RCPs except IPCC (2013) and likely to RCP2.6 by the end of the 21stC Figure SPM.7 exceed 2°C for RCP6.0 and RCP8.5
    17. 17. 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
    18. 18. Temperature changes at the end of the 21st C are dependent on scenario IPCC (2013) Atlas Final Draft, June 7
    19. 19. Climate extremes: more hot and fewer cold extremes IPCC (2013) Table SPM.1
    20. 20. More hot and fewer cold days and nights as global temperatures increase IPCC (2013) Figure 12.13
    21. 21. Australia has observed more hot extremes and fewer cold extremes Hot days Hot nights Cold days Cold nights Courtesy Blair Trewin (BoM)
    22. 22. The contrast between wet and dry regions and wet and dry *with some regional exceptions seasons will increase* 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
    23. 23. The contrast between wet and dry regions and wet and dry seasons will increase IPCC (2013) Atlas Final Draft, June 7
    24. 24. Observed rainfall changes in Australia since 1960 vary seasonally and regionally
    25. 25. Rainfall trends can amplify in streamflow Perth catchment streamflow 1911-2012 (source: WA Water Corporation)
    26. 26. Variability in projections across models: RCP4.5 2046-2065 IPCC (2013) Atlas Final Draft, June 7
    27. 27. Wet extremes over most mid-latitudes land masses and wet tropics will very likely become more intense and more frequent IPCC (2013) Figure 12.26
    28. 28. Few consistent trends in observed extreme rainfall since 1910
    29. 29. The rate of sea level rise is very likely to increase IPCC (2013) Figure SPM.9
    30. 30. Multi-century climate change commitment based on past, present and future emissions of CO2 IPCC (2013) Figure 12.44
    31. 31. CO2 cumulative emissions largely determine late 21stC warming 515 GtC emitted by 2011 IPCC (2013) Figure SPM.10 275 GtC 790 Release of carbon dioxide or methane to the atmosphere from thawing permafrost over the 21stC is assessed to be in the range of 50-250 GtC for RCP8.5 (low confidence)
    32. 32. Headlines of the IPCC 5th 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
    33. 33. Further Information © Yann Arthus-Bertrand / Altitude Email: