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.

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. 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. 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. 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. Global mean surface temperatures increased by 0.89ºC
between 1901 and 2012
Globally averaged surface temperatures
IPCC (2013) Figure SPM.1

6. Almost the entire globe warmed between 1901 and 2012
°C over period
IPCC (2013) Figure SPM.1

7. Warming has occurred almost throughout Australia since 1910
Trend in
Maximum T
°C/10 yrs
Trend in
Minimum T
http://www.bom.gov.au/climate
°C/10 yrs

8. Arctic summer sea ice extent has decreased
IPCC (2013) Figure SPM.3

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. 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. 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. Multiple lines of robust and
compelling evidence
support the conclusion that
many aspects of the climate
system have changed

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. 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. 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. 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. 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. Temperature changes at the end of the 21st C are dependent
on scenario
IPCC (2013) Atlas Final Draft, June 7

19. Climate extremes: more hot and fewer cold extremes
IPCC (2013) Table SPM.1

20. More hot and fewer cold days and nights as global
temperatures increase
IPCC (2013) Figure 12.13

21. Australia has observed more hot extremes and fewer cold
extremes
Hot days
Hot nights
Cold days
Cold nights
Courtesy Blair Trewin (BoM)

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. The contrast between wet and dry regions and wet and dry
seasons will increase
IPCC (2013) Atlas Final Draft, June 7

24. Observed rainfall changes in Australia since 1960 vary
seasonally and regionally
http://www.bom.gov.au/climate

25. Rainfall trends can amplify in streamflow
Perth catchment streamflow 1911-2012 (source: WA Water Corporation)

26. Variability in projections across models: RCP4.5 2046-2065
IPCC (2013) Atlas Final Draft, June 7

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. Few consistent trends in observed extreme rainfall
since 1910
http://www.bom.gov.au/climate

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

30. Multi-century climate change commitment based on past,
present and future emissions of CO2
IPCC (2013) Figure 12.44

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. 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. Further Information
www.climatechange2013.org
© Yann Arthus-Bertrand / Altitude
Email: j.arblaster@bom.gov.au