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samedi 24 décembre 2016

Evénements extrêmes en 2015

Selon les climatosceptiques il n'y aurait pas d'accroissement des événements climatiques extrêmes (de toute façon il n'y a pas pour beaucoup d'entre eux de réchauffement climatique...) mais ils sont incapables d'apporter le moindre arguement sérieux à l'appui de leurs affirmations, à part bien sûr faire référence à des sites climatosceptiques selon le principe du serpent qui se mord la queue ou du raisonnement circulaire du type « j'ai raison parce que j'ai raison, la preuve je vous la fournis avec ce que mon collègue a écrit sur le sujet ! ».

Personnellement je n'ai pas idée, à mon humble niveau de petit terrien, de l'ampleur des événements extrêmes qui se produisent sur la planète, ni si ces événements sont stables, en augmentation ou en diminution ; la mémoire humaine est éminemment faillible et la perception d'un individu biaisée par sa propre expérience, de plus regarder une tempête à la télévision et écouter les commentaires qui vont avec n'aide pas forcément pour se faire une idée claire de la question.

Dans ces conditions je ne trouve qu'une solution, faire confiance aux chercheurs qui ont publié des études sur le sujet en me disant que si elles ne sont pas réfutées ou contredites avec des arguments valables alors c'est que l'on doit les prendre en compte sans sombrer dans la paranoïa complotiste de certains qui croient que les scientifiques sont des charlatans, des fraudeurs ou des incompétents.

Cela tombe bien car est paru récemment un supplément spécial du Bulletin de la Société Américaine de Météorologie dans lequel sont recensés trente événements classés comme extrêmes ayant eu lieu dans le monde en 2015.

Voici le résumé de ces événements que l'on trouvera en fait dans la dernière partie du supplément (chapitre 28) mais que je juge plus utile de faire figurer en tête de mon billet :


On remarquera que sur 30 événements 25 sont imputés à l'action de l'homme, dont 23 avec une influence négative, c'est-à-dire une amplification de l'événement ; seuls 5 sont soit non attribués à l'homme soit incertains quant à leur origine.

A noter qu'en ce qui concerne les événements liés à des chaleurs extrêmes la totalité sont à mettre sur le compte de l'influence anthropique comme il est dit dans l'introduction :
  • Without exception, all the heat-related events studied in this year’s report were found to have been made more intense or likely due to human-induced climate change, and this was discernible even for those events strongly influenced by the 2015 El Niño. 

Voici maintenant les chapitres concernant les événements extrêmes situés dans plusieurs régions du monde ; pour la facilité de lecture et une meilleure compréhension j'ai marqué en rouge les événements ayant une origine anthropique et en vert ceux pour lesquels seule la nature serait à blâmer ; j'ai également précisé entre parenthèses la méthode utilisée afin de savoir notamment si les résultats étaient issus de modèles, d'observations ou des deux.

D'abord l'introduction avec la carte du monde indiquant les endroits où se sont produits les événements.

1. INTRODUCTION TO EXPLAINING EXTREME EVENTS OF 2015 FROM A CLIMATE PERSPECTIVE

Location and types of events analyzed in this publication.

2. MULTIMODEL ASSESSMENT OF ANTHROPOGENIC INFLUENCE ON RECORD GLOBAL AND REGIONAL WARMTH DURING 2015 (CMIP5 modeling)

  • In 2015, record warm surface temperatures were observed for the global mean, India, and the equatorial central Pacific. CMIP5 simulations suggest that for the globe and India, anthropogenic warming was largely to blame.

3. WHAT HISTORY TELLS US ABOUT 2015 U.S. DAILY RAINFALL EXTREMES

  • The United States experienced above-normal daily rainfall extremes in 2015, consistent with national upward trends. However, the most abundant regional extremes were not foreshadowed by co-located long-term seasonal trends. 

4. AN ASSESSMENT OF THE ROLE OF ANTHROPOGENIC CLIMATE CHANGE IN THE ALASKA FIRE SEASON OF 2015 (WRF-ARW optimized for Alaska with metric of fire risk (BUI) to calculate FAR)

  • The 2015 Alaska fire season burned the second largest number of acres since records began in 1940. Human-induced climate change may have increased the risk of a fire season of this severity by 34%–60%.

5. THE 2014/15 SNOWPACK DROUGHT IN WASHINGTON STATE AND ITS CLIMATE FORCING (observations; CESM1 modeling)

  • The 2014/15 snowpack drought resulted from exceedingly high temperatures notwithstanding normal precipitation—a drought type that may reoccur due to accelerated anthropogenic warming and aggravated by naturally driven low precipitation.

6. IN TIDE’S WAY: SOUTHEAST FLORIDA’S SEPTEMBER 2015 SUNNY-DAY FLOOD (tide-gauge data; time-dependent EV Statistical model)

  • The probability of a 0.57-m tidal flood within the Miami region has increased by >500% since 1994 from a 10.9-cm sea level rise (SLR)-related trend in monthly highest tides.

7. EXTREME EASTERN U.S. WINTER OF 2015 NOT SYMPTOMATIC OF CLIMATE CHANGE (Observations; CMIP5 modeling)

  • Despite severe cold waves and record-breaking extreme cold-day occurrences during 2015, no long-term increase in winter daily temperature extremes has occurred in the eastern United States—winters have become warmer and less variable.

8. THE ROLE OF ARCTIC SEA ICE AND SEA SURFACE TEMPERATURES ON THE COLD 2015 FEBRUARY OVER NORTH AMERICA (AMIP (IFS model) modeling)

  • The cold spell of February 2015 in North America was predominantly internally generated; reduced Arctic sea ice and anomalous sea surface temperatures may have contributed in establishing and sustaining the anomalous flow.

9. THE 2015 EXTREME DROUGHT IN WESTERN CANADA (Observations; CMIP5 modeling; Trend and FAR analyses)

  • Analysis results indicate that the 2015 extreme drought in western Canada was likely an outcome of anthropogenically influenced warm spring conditions and naturally forced dry weather from May to July.

10. HUMAN CONTRIBUTION TO THE RECORD SUNSHINE OF WINTER 2014/15 IN THE UNITED KINGDOM (Hadley Centre event attribution system built on the high-resolution version of HadGEM3-A)

  • Extreme winter sunshine in the United Kingdom, as observed in the record high 2014/15 season, has become more than 1.5 times more likely to occur under the influence of anthropogenic forcings.

11. THE ROLE OF ANTHROPOGENIC WARMING IN 2015 CENTRAL EUROPEAN HEAT WAVES (Observations; weather@home modeling)

  • Station-based observations and bias-corrected model simulations show that the frequency of short-term heat waves in central Europe has increased, albeit quantitative estimates of risk ratios differ considerably between methods.

12. THE 2015 EUROPEAN HEAT WAVE (HadGEM3-A modeling)

  • A heat wave swept across central Europe in summer 2015. Model experiments suggest that anthropogenic forcings were a major factor in setting the conditions for the development of the 2015 heat wave.

13. THE LATE ONSET OF THE 2015 WET SEASON IN NIGERIA (Observations; Modeling with CAM5.1 and MIROC5)

  • We find no evidence that the delayed onset of the wet season over Nigeria during April–May 2015 was made more likely by anthropogenic influences or anomalous sea surface temperatures.

14. HUMAN INFLUENCES ON HEAT-RELATED HEALTH INDICATORS DURING THE 2015 EGYPTIAN HEAT WAVE (weather@home modeling)

  • A combined modeling and observational assessment of the 2015 heat wave in Egypt found that human discomfort increased due to anthropogenic climate change.

15. ASSESSING THE CONTRIBUTIONS OF LOCAL AND EAST PACIFIC WARMING TO THE 2015 DROUGHTS IN ETHIOPIA AND SOUTHERN AFRICA (CMIP5 modeling, land surface model simulations, and statistical analyses)

  • Anthropogenic warming contributed to the 2015 Ethiopian and southern African droughts by increasing El Niño SSTs and local air temperatures, causing reduced rainfall and runoff, and contributing to severe food insecurity.

16. THE DEADLY COMBINATION OF HEAT AND HUMIDITY IN INDIA AND PAKISTAN IN SUMMER 2015 (Non-stationary EV theory; C20C+ Attribution Subproject)

  • We find that the deadly heat waves in India and Pakistan in 2015 were exacerbated by anthropogenic climate change. Although the impacts of both events were severe, the events themselves were not connected to each other.

17. THE HEAVY PRECIPITATION EVENT OF DECEMBER 2015 IN CHENNAI, INDIA (Observations; Modeling with weather@home, EC-Earth and CMIP5)

  • Extreme one-day rainfall caused widespread flooding in Chennai, India, in December 2015. No effect of global warming was detected, likely caused by aerosols counteracting greenhouse gases up to now.

18. ATTRIBUTION OF EXTREME RAINFALL IN SOUTHEAST CHINA DURING MAY 2015 (HadGEM3-A-N216 modeling; FAR)

  • Anthropogenic climate change increased the probability that a short-duration, intense rainfall event would occur in parts of southeast China. This type of event occurred in May 2015, causing serious flooding.

19. RECORD-BREAKING HEAT IN NORTHWEST CHINA IN JULY 2015: ANALYSIS OF THE SEVERITY AND UNDERLYING CAUSES (CMIP5 modeling with ROF; FAR)

  • The record-breaking heat over northwest China in July 2015 was linked directly to atmospheric general circulation indices and anthropogenic forcing. The latter increased the risk of extreme heat by three-fold.

20. HUMAN INFLUENCE ON THE 2015 EXTREME HIGH TEMPERATURE EVENTS IN WESTERN CHINA (CMIP5 modeling with ROF; FAR)

  • Human influence has very likely increased the probability of occurrence of the 2015 western China extreme summer temperature events by at least 3-fold and 42-fold for the highest daily maximum and minimum temperatures, respectively.

21. A PERSISTENT JAPANESE HEAT WAVE IN EARLY AUGUST 2015: ROLES OF NATURAL VARIABILITY AND HUMAN-INDUCED WARMING (MIROC5-AGCM modeling)

  • The persistent Japanese heat wave that occurred in early August 2015 was mainly attributed to intraseasonal disturbances including tropical cyclones. Anthropogenic warming contributed to an increase in the probability of occurrence.

22. CLIMATE CHANGE AND EL NIÑO INCREASE LIKELIHOOD OF INDONESIAN HEAT AND DROUGHT (Observations; CMIP5 modeling)

  • El Niño and human-induced climate change have substantially increased the likelihood of rainfall deficits and high temperatures, respectively, in Indonesia such as those experienced in the drought conditions of J ul y – Oc t ober 2015.

23. SOUTHERN AUSTRALIA’S WARMEST OCTOBER ON RECORD: THE ROLE OF ENSO AND CLIMATE CHANGE (weather@home modeling; FAR)

  • Anthropogenic climate change was found to have a substantial influence on southern Australia’s extreme heat in October 2015. The relative influence of El Niño conditions was less clear.

24. WHAT CAUSED THE RECORD-BREAKING HEAT ACROSS AUSTRALIA IN OCTOBER 2015? (BoM seasonal forecast attribution system and seasonal forecasts)

  • Using a seasonal forecasting framework for attribution, we find that half of the record heat anomaly across Australia in October 2015 can be attributed to increasing CO2, with much of the rest due to internal atmospheric variability.

25. THE ROLES OF CLIMATE CHANGE AND EL NIÑO IN THE RECORD LOW RAINFALL IN OCTOBER 2015 IN TASMANIA, AUSTRALIA (Observations; Modeling with CMIP5 and weather@home)

  • Anthropogenic climate change and El Niño made small but significant contributions to increasing the likelihood of record low rainfall in October 2015 in Tasmania. Atmospheric variability was the main contributor.

26. INFLUENCES OF NATURAL VARIABILITY AND ANTHROPOGENIC FORCING ON THE EXTREME 2015 ACCUMULATED CYCLONE ENERGY IN THE WESTERN NORTH PACIFIC (GFDL FLOR modeling; FAR)

  • The extreme value of the 2015 western North Pacific (WNP) accumulated cyclone energy (ACE) was mainly caused by the sea surface warming in the eastern and central Pacific, with the anthropogenic forcing largely increasing the odds of the occurrence of this event.

27. RECORD LOW NORTHERN HEMISPHERE SEA ICE EXTENT IN MARCH 2015 (OGCM modeling)

  • The record low Northern Hemisphere (NH) winter sea ice maximum stemmed from a strong interannual surface anomaly in the Pacific sector, but it would not have been reached without long-term climate change.

28. SUMMARY AND BROADER CONTEXT

  • This year’s event types include tropical cyclones, extreme sunshine, nuisance tidal flooding, snowpack drought, forest fires, and Arctic sea ice extent in addition to heat, cold, precipitation, and drought. The Summary Table (Table 28.1) is provided to give readers a general overview of the results. However, it is a highly simplified categorization of the results and does not include information about the size of the signal detected or the confidence in the results. This information is found within each individual report and provides essential context for understanding and interpreting results for any individual event. Also, while these reports may be the first analysis for many of these events, they may not be the last. Additional research on any of these events may uncover new information that helps provide a more complete understanding for the role of climate change.
 La table 28.1 dont il est question est celle qui figure en tête de ce billet.


  La définition des acronymes figure au bas de ce tableau dans le document.

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