1. Attribution of Climate-related Events
Nikos Christidis, Peter A Stott, Nikos Christidis, Andrew Ciavarella, Fraser Lott, Adam Scaife, Alberto Arribas
EUCLEIA 1st General Assembly, ETH Zurich, 20 January 2014
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2. Outline Why? Attribution of Climate-related Events BAMS annual reports
EUCLEIA
Met Office Operational Attribution System
Communication
© Crown copyright Met Office

3. January, 2014
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4. This winter : the wettest winter in England and Wales since 1766

5. “Human influence on the climate system is clear.”
AR5 WGI SPM

6. “It is virtually certain there will be more frequent hot extremes.”
“Extreme precipitation events over most of the mid latitudes and wet tropical regions will very likely become more intense and more frequent.”

7. Are all extreme weather and climate events due to human-induced greenhouse gas emissions?
Do we need to adapt to a greater frequency of such events in future or not?
Misattribution, eg by attributing every extreme weather event to anthropogenic climate change could lead to poor adaptation decisions.
Pakistan flooding, 2010
Russian heatwave, 2010
Queensland floods, Jan 2011
Cold winters, UK, 2009, 2010
East African drought, 2011
© Crown copyright Met Office
© Crown copyright Met Office

8. Outline Why? Attribution of Climate-related Events BAMS annual reports
EUCLEIA
Met Office Operational Attribution System
Communication

9. Attribution statements can be made about individual climate events by examining the changed probability
European heatwave, 2003
Very likely more than doubled the probability (Stott et al)
Australian heatwave, 2013
Very likely increased the probability by more than 2.5 times (Lewis et al)

10. Attribution of an individual climate event : application of probabilistic event attribution to the very hot European summer of 2003
Human influence very likely (>90% confidence level) at least doubled the probability of European summer temperatures as hot as Stott et al, Nature, 2004.
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13. Outline Motivation Attribution of Climate-related Events
BAMS annual reports
EUCLEIA
Met Office Operational Attribution System
Communication

14. Climate change has made some events more likely, some less likely
Explaining extreme climate and weather events of the previous year from a climate perspective Tom Peterson, Martin Hoerling, Peter Stott, Stephanie Herring.
Report ground breaking in applying attribution science to recent extreme weather events.
Climate change has made some events more likely, some less likely
We do not see evidence for a strong human influence in all weather extremes. Natural variability also plays an important role
Inaugural report quickly became “most read” article in BAMS
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15. Increase from 6 contributions last year to 19 this year
Explaining extreme climate and weather events of the previous year from a climate perspective Tom Peterson, Martin Hoerling, Peter Stott, Stephanie Herring.
Increase from 6 contributions last year to 19 this year
18 different research groups, 12 extreme events
Some events have multiple different groups looking at them
About half the analyses found some evidence that anthropogenic climate change was a contributing factor
Natural climate variability a factor in all events
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16. Iberian winter drought Trigo et al, 2013 (BAMS report)
A tendency towards a drier Mediterranean driven by anthropogenic emissions of greenhouse gases and aerosols, although modulated by the NAO phase.
Pics below are taken from Hoerling et al
Expect 3 winter droughts per century in current decade compared to expectation of 2.4 winter droughts per century in 1960s
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17. Extreme rainfall, New Zealand Dean et al, 2013 (BAMS report)
An atmospheric river brought very high levels of moisture, extreme rainfall and landslides to the mid-latitude location of Golden Bay, New Zealand on 14 December, 2011.
Pics below are taken from Hoerling et al
Total moisture available for precipitation in this event has increased by 1% to 5% as a result of the emission of greenhouse gases.
Models show an increase in the frequency of such events of between 8 and 32%.
Predominantly due to a thermodynamic response.
© Crown copyright Met Office

18. Outline Why? Attribution of Climate-related Events BAMS annual reports
EUCLEIA
Met Office Operational Attribution System
Communication
© Crown copyright Met Office

19. EUropean CLimate and weather Events : Interpretation and Attribution
Heatwaves
Cold spells
Floods
Droughts
Storm surges
UK Met Office
ETH Zurich
CNRS
University of Edinburgh
IC3
DMI
KNMI
University of Reading
University of Oxford
HZG
Université de Versailles
© Crown copyright Met Office

20. Main limitations at present
Event attribution studies attempted only for a small number of specific cases
There can be apparently conflicting results for the same event
Attribution results rely heavily on models whose limitations may not be fully understood
Biases and poor sampling in observational datasets
The requirements for such attribution studies are not well understood
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21. Project Objectives
Derive the requirements of targeted user groups for attribution products and demonstrate value to these users of attribution products developed under EUCLEIA (WP4)
Develop experimental designs and clear ways of framing attribution studies (WP5)
Develop methodology for representing level of confidence in attribution results (WP6)
Demonstrate utility of attribution system on a set of test cases (WP7)
Produce traceable and consistent attribution assessments (WP8)
Fast-track in immediate aftermath
Seasonal basis to stakeholder groups
Annual basis to BAMS attribution report
Coordination between the FP7 Copernicus climate change projects (WP9)
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22. 5 FP7-SPACE projects prepare for a Copernicus Climate Change Service:
ERA-CLIM2 (global reanalysis, Dick Dee, ECMWF)
UERRA (regional reanalysis, Per Unden, SMHI)
QA4ECV (air quality ECVs, Folkert Boersma, KNMI)
CLIPC (climate impact platform, Martin Juckes, STFC)
EUCLEIA (event attribution, Peter Stott, Met Office)
The overarching WP will co-ordinate information exchange between these projects and the outside world, including relevant Commission DGs and joint stakeholders

23. Outline Why? Attribution of Climate-related Events BAMS annual reports
EUCLEIA
Met Office Operational Attribution System
Communication
© Crown copyright Met Office

27. Coupled model assessments
Annual mean T distributions in Giorgi regions
Red: with human influences
Green: without human influences
Vertical black lines: Max temperature in CRUTEM3
© Crown copyright Met Office

28. Attribution of Climate-related Events (ACE) Development of the Hadley Centre near-real time attribution system
ACE approach:
Generate large ensembles (perturbing physics parameters), running our model with observed SSTs and external forcings.
Generate a second ensemble without the human influence. An estimate of the anthropogenic change in the SSTs is subtracted from the observations. Only natural forcings are included.
Change in the likelihood of the event
given certain modes of internal variability
Hadley Centre near-real time attribution system
HadGEM3-A, N96 L38. (Currently upgrading to N216 L85)
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29. Patterns of the change in the SST
January
April
July
October
HadGEM1
HadCM3
HadGEM2-ES
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30. Validation Dec-Jan UK Temperature
Timeseries
Distributions
Power Spectrum
Red Lines: NCEP/NCAR Reanalysis
Black Lines: 5 Model runs with ALL forcings and observed SSTs & SI
© Crown copyright Met Office

31. Validation July Rainfall in Pakistan
Timeseries
Distributions
Power Spectrum
Red Lines: NCEP/NCAR Reanalysis
Black Lines: 5 Model runs with ALL forcings and observed SSTs & SI
© Crown copyright Met Office

32. Greater Horn Short Rains (SON) Temperature and Rainfall
Above median temperature
Below median rainfall
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33. Greater Horn Long Rains (MAM) Temperature and Rainfall
Above median temperature
Below median rainfall
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34. Next steps 1st Year: Finalise the model upgrade
Produce long simulations (1960-present)
Development of coupled model response techniques
Update pre-computed FAR tables
2nd Year:
Generate ensembles for targeted test cases
Investigate extremes for the BAMS report
Development and application of fast-track response techniques
3rd Year:
Delivery of an operational event attribution system
Delivery of assessments for the BAMS report
Reports on fast-track response assessments and the new attribution service
© Crown copyright Met Office

35. Human influence on the climate system is clear
Better understanding of the changing risks of extreme weather will help people cope with the effects of anthropogenic climate change.
Extreme weather and seasons result from the interplay of natural climate variability and anthropogenic climate change.
At the Met Office we are developing an “operational attribution” system to assess the risks of such extremes on a regular basis.
A new annual report provides puts extreme weather from last year in different regions of the world into the context of natural climate variability and anthropogenic climate change.
© Crown copyright Met Office
© Crown copyright Met Office

36. Any questions?
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37. Australia
January 2013

38. Hobart, Tasmania, 4th January 2013

39. Dunalley, 4th January 2013

40. Dunalley, 4th January 2013

41. AR5 WGI SPM approved line-by-line in Stockholm by 110 governments

42. Extreme rainfall, New Zealand Dean et al, 2013 (BAMS report)
An atmospheric river brought very high levels of moisture, extreme rainfall and landslides to the mid-latitude location of Golden Bay, New Zealand on 14 December, 2011.
Pics below are taken from Hoerling et al
Total moisture available for precipitation in this event has increased by 1% to 5% as a result of the emission of greenhouse gases.
Models show an increase in the frequency of such events of between 8 and 32%.
Predominantly due to a thermodynamic response.
© Crown copyright Met Office