BAMS Report: Extreme Weather Events of 2012 from a Climate Perspective

BAMS Report: Extreme Weather Events of 2012 from a Climate Perspective

The Bulletin of the American Meteorological Society (BAMS) has just released a comprehensive study of 12 different extreme weather events of 2012 and whether or not human-caused climate change "Anthropogenic Global Warming" (AGW) may have played a role in the severity of each event. 78 climate scientists from around the world took part in this peer-reviewed study. Here is a brief summary of the reports conclusions.

The 12 events scrutinized were:

1. U.S. Heat Wave of July 2012

2. U.S. Heat Wave of March-May 2012

3. Hurricane Sandy

4. September 2012 Arctic Sea Ice Minimum

5. February 2012 Western European Cold Wave

6. Extreme Rainfall Variation in Europe Summer of 2012

7. Record Winter Drought on Iberian Peninsula 2011-2012

8. Rainfall Deficits in Eastern Kenya and Southern Somalia 2012 and 2003-2012

9. North China Floods of 2012

10. Heavy Rainfall in Southwestern Japan in 2012

11. Heavy Rainfall over Eastern Australia in March 2012

12. Two-day Extreme Rainfall Event in Golden Bay, New Zealand during December 2011



Locations of the 12 extreme weather and climate events covered in the BAMS report ‘Explaining Extreme Weather Events of 2012 From a Climate Perspective’.

NOAA’s Communications & External Affairs Department released a media statement today (September 5th) citing the report and keynoting some its ‘KEY FINDINGS’:

Heat Wave and Drought in United States:


Human-induced climate change had little impact on the lack of precipitation in the central United States in 2012.

The 2012 spring and summer heat waves in the U.S. can be mainly explained by natural atmospheric dynamics, however, human-induced climate change was found to be a factor in the magnitude of warmth and was found to have affected the likelihood of such heat waves. For example:

High temperatures, such as those experienced in the U.S. in 2012 are now likely to occur four times as frequently due to human-induced climate change.

Approximately 35 percent of the extreme warmth experienced in the eastern U.S. between March and May 2012 can be attributed to human-induced climate change.


Hurricane Sandy Inundation Probability:


The record-setting impacts of Sandy were largely attributable to the massive storm surge and resulting inundation from the onshore-directed storm path coincident with high tide. However, climate-change related increases in sea level have nearly doubled today's annual probability of a Sandy-level flood recurrence as compared to 1950. Ongoing natural and human-induced forcing of sea level ensures that Sandy-level inundation events will occur more frequently in the future from storms with less intensity and lower storm surge than Sandy.


Arctic Sea Ice:


The extremely low Arctic sea ice extent in summer 2012 resulted primarily from the melting of younger, thin ice from a warmed atmosphere and ocean. This event cannot be explained by natural variability alone. Summer Arctic sea ice extent will continue to decrease in the future, and is expected to be largely absent by mid-century.




Cover of the BAMS report.

Some Other Conclusions from the Report

The BAMS report is, of course, extremely detailed and aimed at a scientific audience. In all there were 19 different analyses made by 18 different research groups (some of the analyses covered the same extreme events). As is usual in scientific papers the conclusions were not ‘set in stone’ and came to a variety of different views so far as what role AGW played in each event. I recommend everyone to read the report for themselves to be found in its entirety here but will provide a snapshot of how each event was rated so far as AGW being complicit in each event's intensity:


1. U.S. Heat Wave of July 2012
(AGW likely to have played a role)

2. U.S. Heat Wave of March-May 2012
(AGW likely to have played a role)

3. Hurricane Sandy
(AGW did not play a role in the storm itself but may make such storms more destructive in the future due to AGW-driven sea rise)

4. September 2012 Arctic Sea Ice Minimum
(AGW played a role although a severe Arctic storm in August 2012 was also a contributing factor)

5. February 2012 Western European Cold Wave
(AGW probably not a factor)

6. Extreme Rainfall Variation in Europe Summer of 2012
(AGW may have played a role along in combination with several other factors)

7. Record Winter Drought on Iberian Peninsula 2011-2012
(AGW most likely played a role "modulated" by the NAO phase)

8. Rainfall Deficits in Eastern Kenya and Southern Somalia 2012 and 2003-2012
(not clear what, if any, role AGW played)

9. North China Floods of 2012
(not clear what, if any, role AGW played)

10. Heavy Rainfall in Southwestern Japan in 2012
(AGW unlikely to have played a role)

11. Heavy Rainfall over Eastern Australia in March 2012
(AGW unlikely to have played a role although warming ocean temperatures a factor)

12. Two-day Extreme Rainfall Event in Golden Bay, New Zealand during December 2011
(AGW may have played a role in so far as increased moisture in the atmosphere)


I hope I have summarized the AGW component correctly for each of the above cases. Some of the concluding remarks were so long and complex it was a bit difficult to ‘summarize’ them concisely. I therefore highly recommend reading the report for yourselves and determine if you agree with my brief summaries above (so far as the influence of AGW).

CITATION FOR COMPLETE REPORT: Peterson,, T.C., M.P. Hoerling, P.A. Stott and S. Herring, Eds., ‘Explaining Extreme Events of 2012 from a Climate Perspective’. Bulletin of the American Meteorological Society, Vol. 94 (9), S1-S74.. Report is here.

Christopher C. Burt
Weather Historian