Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Tuesday 7 July - 16:30-18:00 UNESCO Fontenoy - ROOM VI

1118 (a) - Attribution of extreme events: How are high impact extreme events changing and why ?

Parallel Session

Lead Convener(s): S. Planton (Météo-France, Toulouse, France), R. Vautard (LSCE-IPSL, Gif-sur-Yvette, France)

Convener(s): P. Stott (UK Meteorological Office, Exeter, United Kingdom), D. Coumou (Potsdam Institute for Climate Impact Research, Potsdam, Germany), W. Cramer (IMBE, Marseille, France), F. Zwiers (Univesity of Victoria, Vancouver, Canada)

16:30

Are humans exacerbating climate and weather extremes?

F. Zwiers (Univesity of Victoria, Vancouver, Canada)

Abstract details
Are humans exacerbating climate and weather extremes?

F. Zwiers (1)
(1) Univesity of Victoria, Vancouver, Canada

Abstract content

This talk will review some of the recent research on extremes, pointing to aspects of changes in extremes in which we have higher and lower levels of confidence.  The body of evidence indicating a human contribution to observed climate change has continued to strengthen as indicated by the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). This continued development includes an accumulating body of evidence suggesting that temperature and precipitation extremes have both changed in response to human influences on the climate. The research on temperature extremes is well established, with recent work indicating that temperature extremes have continued to warm over land despite the recent global warming “hiatus”, and that anthropogenic forcing has substantially increased the odds of extreme warm years and summers, both globally and regionally. The evidence on precipitation extremes is less well established, although there is increasingly strong evidence that human influence is detectable in observations at the largest scales that are resolvable in available international compilations of daily precipitation records. In contrast, assessments of historical and projected changes in droughts and storminess remain cautious, due to both data limitations and uncertainty in process understanding and modelling. Despite uncertainties and limitations in knowledge, observed and projected changes in the simple temperature and precipitation indicators in which we have greatest confidence provide ample evidence that adaptation is required now, and that further adaptation will be required in the future under all RCP forcing scenarios.

16:50

Detecting and attributing impacts of recent climate change on multiple systems worldwide – certainties, uncertainties and new research questions

W. Cramer (IMBE, Aix-en-Provence, France), G. Hansen, (Potsdam Institute for Climate Impact Research, Potsdam, Germany), M. Auffhammer (University of California, Berkeley CA, United States of America), C. Huggel (University of Zürich, Zürich, Switzerland), D. Stone (Berkeley Lab, Berkeley CA, United States of America)

Abstract details
Detecting and attributing impacts of recent climate change on multiple systems worldwide – certainties, uncertainties and new research questions

W. Cramer (1) ; G. Hansen, (2) ; M. Auffhammer (3) ; C. Huggel (4) ; D. Stone (5)
(1) IMBE, Cnrs, aix marseille university, ird, avignon university, Aix-en-Provence, France; (2) Potsdam Institute for Climate Impact Research, Potsdam, Germany; (3) University of California, Berkeley CA, United States of America; (4) University of Zürich, Department of geography, Zürich, Switzerland; (5) Berkeley Lab, Berkeley CA, United States of America

Abstract content

Due to rapidly growing scientific evidence, based on growing stocks of observations as well as on improved methodologies, it is widely accepted that recent climate change has triggered changes in numerous systems worldwide. Most cited examples concern hydrological systems, the cryosphere, and many biological systems in the ocean and on all continents. The recent IPCC assessment, which was based on an unprecedented trans-disciplinary community effort, found more widespread impacts than previous reports, covered a greater range of impacted system types but also identified regions and systems with insufficient research and monitoring effort. Updating the report, three key questions will be addressed: a) To which extent have human systems been impacted, either directly or through cascading impacts through natural systems? b) How much is known about impacts in poorly observed regions? c) To which extent can the impacts of anthropogenic climate change be distinguished from those of natural climate variability?

17:10

Attribution of extreme events : Taking attribution science to the limits

P. Stott (UK Meteorological Office, Exeter, United Kingdom)

Abstract details
Attribution of extreme events : Taking attribution science to the limits

P. Stott (1)
(1) UK Meteorological Office, Hadley Centre, Exeter, United Kingdom

Abstract content

Around the World recent heatwaves, floods and droughts have demonstrated the vulnerability of citizens to such extreme weather.  However, scientifically robust information about the extent to which recent extreme weather events can be linked to climate variability and change is often lacking. There is therefore a clear need to develop better information on weather and climate risks as part of the development of climate services to enable citizens to better deal with the effects of climate change.

 

This paper describes recent progress in developing the science needed to deliver such much needed reliable and timely information about weather and climate risks. It focuses on two important developments in particular.

 

An annual report published each September in the Bulletin of the American Meteorological Society seeks to explain extreme events of the previous year from a climate perspective. This report has demonstrated the capability to deliver assessments relatively quickly while also showing how the scientific capabilities to carry out such studies is developing rapidly with an increasing number of types of event being considered  with larger geographical coverage.  

 

One of the main international groups working to further the development of this science is the EUCLEIA project, a European funded project with eleven partners. EUCLEIA (European CLimate and weather Events: Interpretation and Attribution) is developing an attribution system to deliver reliable and user-relevant attribution assessments on a range of timescales; on a fast track basis in the immediate aftermath of extreme events, on a seasonal basis to stakeholder groups and annually to the annual attribution reports in the Bulletin of the American Meteorological Society.

 

We will illustrate the presentation with some of the main scientific highlights of this work while also exploring how such scientific information can be best developed and applied in future.

17:30

Attribution of record high daily temperatures in Australia in 2013

D. Karoly (University of Melbourne, University of Melbourne, VIC, Australia), M. Black (University of Melbourne, University of Melbourne, VIC, Australia), S. Lewis, (Australian National University, Canberra, Australia), A. King (University of Melbourne, Melbourne, Victoria, Australia), M. Allen (University of Oxford, Oxford, United Kingdom), F. Otto (University of Oxford, Oxford, United Kingdom), S. Rosier, (NIWA, Wellington, New Zealand)

Abstract details
Attribution of record high daily temperatures in Australia in 2013

D. Karoly (1) ; M. Black (1) ; A. King (2) ; M. Allen (3) ; F. Otto (4) ; S. Rosier, (5) ; S. Lewis, (6)
(1) University of Melbourne, School of Earth Sciences, University of Melbourne, VIC, Australia; (2) University of Melbourne, School of Earth Sciences, Melbourne, Victoria, Australia; (3) University of Oxford, School of Geography and Environment and Dept of Physics, Oxford, United Kingdom; (4) University of Oxford, Oxford, United Kingdom; (5) NIWA, Wellington, New Zealand; (6) Australian National University, School of earth sciences, Canberra, Australia

Abstract content

There has been increasing scientific interest in understanding the climate factors associated with extreme weather and climate events. This has led to the series of special supplements in the Bulletin of the American Meteorological Society over the last three years on “Explaining Extreme Events from a Climate Perspective”. A wide range of extreme events has been considered in the studies included in these supplements, ranging from heavy rainfall and drought events to record hot and cold seasons. However, there have been no studies so far on the attribution of record high daily temperatures at single sites.

 

The Australian summer of 2012-13 was the hottest summer averaged across Australia since reliable records began in 1910. Lewis and Karoly (2013) showed that human influences on climate have very likely increased the likelihood of extreme summer average temperature across Australia such as in 2012-13 by at least a factor of five. Here we present an analysis of the contribution of human-caused climate change to the frequency of events such as the record high daily temperatures that occurred across Australia on 7 January 2013 and in Sydney on 18 January 2013. 

 

The recently launched citizen science distributed computing project weather@home ANZ 

( http://www.climateprediction.net/weatherathome/australia-new-zealand-heat-waves/ )

has generated very large ensembles of simulated regional daily weather data needed for the attribution of extreme events. By comparing the frequency of extreme daily temperatures in the model simulations for 2013 and for a counter-factual world without any human influences on the regional climate, we assess the role of human influences on the likelihood of these two cases of record high daily temperatures in Australia in 2013. 

 

Lewis, S.C., and D. J. Karoly (2013) Anthropogenic contributions to Australia’s record summer temperature of 2013. Geophys. Res. Lett., 40, 3705-3709. DOI: 10.1002/grl.50673

17:40

Human influence on climate in the 2014 Southern England winter floods and their impacts

N. Schaller (University of Oxford, Oxford, United Kingdom), A. Kay (CEH, Wallingford, United Kingdom), R. Lamb (JBA, Skipton, United Kingdom), N. Massey (University of Oxford, Oxford, United Kingdom), G. J. Van Oldenborgh (KMNI, De Bilt, Netherlands), F. Otto (University of Oxford, Oxford, United Kingdom), S. Sparrow (University of Oxford, Oxford, United Kingdom), R. Vautard (Laboratoire des Sciences du Climat et de l'Environnement, Saclay, France), P. Yiou (Laboratoire des Sciences du Climat et de l'Environnement, Saclay, France), A. Bowery (University of Oxford, Oxford, United Kingdom), S. Crooks (CEH, Wallingford, United Kingdom), C. Huntingford (CEH, Wallingford, United Kingdom), W. Ingram (University of Oxford, Oxford, United Kingdom), R. Jones (Met Office, Exeter, United Kingdom), T. Legg (Met Office, Exeter, United Kingdom), J. Miller (University of Oxford, Oxford, United Kingdom), D. Wallom (University of Oxford, Oxford, United Kingdom), A. Weisheimer (University of Oxford, Oxford, United Kingdom), P. Stott (UK Meteorological Office, Exeter, United Kingdom), M. Allen (University of Oxford, Oxford, United Kingdom)

Abstract details
Human influence on climate in the 2014 Southern England winter floods and their impacts

N. Schaller (1) ; A. Kay (2) ; R. Lamb (3) ; N. Massey (1) ; GJ. Van Oldenborgh (4) ; F. Otto (1) ; S. Sparrow (1) ; R. Vautard (5) ; P. Yiou (5) ; A. Bowery (1) ; S. Crooks (2) ; C. Huntingford (2) ; W. Ingram (1) ; R. Jones (6) ; T. Legg (6) ; J. Miller (1) ; D. Wallom (1) ; A. Weisheimer (1) ; P. Stott (7) ; M. Allen (1)
(1) University of Oxford, Oxford, United Kingdom; (2) CEH, Wallingford, United Kingdom; (3) JBA, Skipton, United Kingdom; (4) KMNI, De Bilt, Netherlands; (5) Laboratoire des Sciences du Climat et de l'Environnement, Saclay, France; (6) Met Office, Exeter, United Kingdom; (7) UK Meteorological Office, Hadley Centre, Exeter, United Kingdom

Abstract content

The whole winter of 2013/2014 was characterized by a near-continuous succession of westerly storms. Accumulated rainfall during January 2014 was the largest ever recorded for that month across much of southern England, including the Radcliffe Observatory record in Oxford that begins in 1767. Severe floods resulted, causing major disruption.

So far, quantifying any contribution from human influence on climate to such weather events and resulting floods has been difficult due to the large natural variability of winter precipitation in the North Atlantic and European regions. The emerging science of probabilistic event attribution however increasingly allows us to evaluate the extent to which human-induced climate change is affecting localised weather events. Under the project “EUropean CLimate and weather Events: Interpretation and Attribution” (EUCLEIA), an end-to-end attribution study is performed for the first time. An ensemble of 134,354 general circulation model simulations is run using the citizen science project weather@home. We find that the frequency of days in January in zonal flows increases jointly with increases in precipitation as a result of anthropogenic climate change. The best estimate of the change in risk of extreme (1-in-100-year in pre-industrial conditions) precipitation for January in southern England is an increase by 42%, but the uncertainty range includes no change or an increase by over 150% due to uncertainty in the pattern of anthropogenic warming. Further, we partition the impact of greenhouse gases to dynamic changes in atmospheric circulation and to thermodynamic increasing water loading, demonstrating that both mechanisms played a role. A hydrological model driven by the model-simulated precipitation gives similar increases in risk compared to precipitation for 30-day peak river flows for the Thames at Kingston. Given these river flows we estimate that anthropogenic climate change has placed an additional 3,500 properties in the Thames catchment (upstream of the tidal reach through London) at risk of flooding from rivers over a broad range of return-times. Our study provides for the first time an estimate of the scale of precipitation-related damages in a specific region due to the effects of anthropogenic changes in the composition of the atmosphere on climate.

17:50

Role of soil moisture vs. recent climate change for heat waves in western Russia

M. Hauser (ETH, Zurich, Zurich, Switzerland), R. Orth (ETH, Zurich, Zurich, Switzerland), S. Seneviratne (ETH, Zurich, Zurich, Switzerland)

Abstract details
Role of soil moisture vs. recent climate change for heat waves in western Russia

M. Hauser (1) ; R. Orth (1) ; S. Seneviratne (1)
(1) ETH, Zurich, Institute for atmospheric and climate science, Zurich, Switzerland

Abstract content

Using the framework of event attribution, anthropogenic climate change was found to have a discernible influenceon the occurence-probability of heat waves, such as the one in Russia in 2010. Soil moisture, on the other hand, is an important physical driver for heat waves as its availability has a large influence on the partitioning of the available surface net radiation into latent and sensible heat flux. The presented study investigates the relative importance of both controls, soil moisture and increasing greenhouse gas concentrations, on heat waves in the region of the 2010 Russian heat wave. This is done with a large number of ensemble members from climate simulations with and without interactive soil moisture for both, the 2000s and the 1960s. The simualtions allow to determine the occurence-probability of heat waves with and without the soil moisture-temperature feedback and to compare it to the warming caused by climate change. Thereby, we expect to see the largest effect on daytime maximum temperatures (TXx) and a smaller influence of soil moisture on the mean temperatures and cold extremes.