Study: Global warming is driving increased frequency of extreme wet or dry summer weather in southeast, so droughts and deluges are likely to get worse

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"Study: Global warming is driving increased frequency of extreme wet or dry summer weather in southeast, so droughts and deluges are likely to get worse"

A new study by a Duke University-led team of climate scientists suggests that global warming is the main cause of a significant intensification in the North Atlantic Subtropical High (NASH) that in recent decades has more than doubled the frequency of abnormally wet or dry summer weather in the southeastern United States.

Increasingly Variable Summer Rainfall in Southeast Linked to Climate Change The NASH, commonly referred to as the Bermuda High, is an area of high pressure that forms each summer near Bermuda, where its powerful surface center helps steer Atlantic hurricanes and plays a major role in shaping weather in the eastern United States, Western Europe and northwestern Africa.

That’s from the Duke University news release for a new study in the Journal of Climate.

In a September 2009 post, “Hell and High Water hits Georgia,” I noted that, “as climate scientists have predicted for a long time, wild climate swings are becoming the norm, in this case with once-in-a-century drought followed by once-in-a-century flooding.”  And in fact, the flooding was more like a once in 500 year event.

Now a team of scientists has quantified the rise in extreme wet and dry summer weather — and finds global warming is likely the main cause.  The release continues:

By analyzing six decades of U.S. and European weather and climate data, the Duke-led team found that the center of the NASH intensified by 0.9 geopotential meters a decade on average from 1948 to 2007.  (Geopotential meters are used to measure how high above sea level a pressure system extends; the greater the height, the greater the intensity.

The team’s analysis found that as the NASH intensified, its area enlarged, bringing the high’s weather-making western ridge closer to the continental United States by 1.22 longitudinal degrees a decade.

“This is not a natural variation like El Nino,” says lead author Wenhong Li, assistant professor of earth and ocean sciences at Duke University’s Nicholas School of the Environment.   “We thoroughly investigated possible natural causes, including the Atlantic Multivariate Oscillation (AMO) and Pacific Decadal Oscillation (PDO), which may affect highs, but found no links.

“Our analysis strongly suggests that the changes in the NASH are mainly due to anthropogenic warming,” she says.

An early online edition of the study, published in the Journal of Climate, is available at the American Meteorological Society’s website at http://journals.ametsoc.org/doi/pdf/10.1175/2010JCLI3829.1.

The study has a firewall.  For the text alone, you can get around it here.

As the NASH intensified and migrated westward, Li’s team’s analysis found that its meridional variation, or north-south movement, also was enhanced from 1978 to 2007, a period when the frequency of extreme summer rainfall variability in the Southeast more than doubled over the previous 30 years.  From 1978 to 2007, 11 summers – defined in this study as the months of June, July and August – had total seasonal precipitation anomalies greater than one standard deviation from the mean.  Six of the summers were abnormally wet, while five were abnormally dry.

To forecast future trends in the NASH’s intensity, the team used climate models developed for use by the Intergovernmental Panel on Climate Change’s Fourth Assessment Report in 2007. The models – known as  Coupled Model Intercomparison Project Phase 3 (CMIP3) models – predict the NASH will continue to intensify and expand as concentrations of carbon dioxide and other greenhouse gases increase in Earth’s atmosphere in coming decades.

This intensification will further increase the likelihood of extreme summer precipitation variability – periods of drought or deluge – in southeastern states in coming decades,” Li says.

If the NASH ‘s western ridge’s meridional movement jogs a little to the north as it expands, the likelihood increases for more extreme dry weather in the Southeast that summer, she explains. If the NASH wobbles a little to the south, extreme wet weather becomes more likely….

In addition to long-term rainfall data and the CMIP3 models, the team used atmospheric reanalysis data from the U.S. National Center for Environmental Prediction/National Center for Atmospheric Research and the European Centre for Medium-Range Weather Forecasts to conduct the study.

For a meteorologist’s take on the amazing 2009 Georgia flooding, also using the NCEP reanalysis data, see “Weather Channel expert on Georgia’s record-smashing global-warming-type deluge.”

The peer-reviewed analysis concludes that “the NASH system will likely intensify, expand and move further westward in the 21st century with the increase of CO2, indicating increased likelihoods of both extreme rainfall events and droughts over the SE US in the future.”

The scary part, as I’ve said many times, is that we’ve only warmed about a degree Fahrenheit in the past half-century.  We are on track to warm nearly 10 times that this century (see M.I.T. doubles its 2095 warming projection to 10°F “” with 866 ppm and Arctic warming of 20°F ).  And that’s just business as usual.  The plausible worst-case scenario is beyond comprehension:

Drought and deluge — Hell and High Water — we ain’t seen nothing yet!

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23 Responses to Study: Global warming is driving increased frequency of extreme wet or dry summer weather in southeast, so droughts and deluges are likely to get worse

  1. Scrooge says:

    Absolutely understandable IMO this goes along with deserts expanding throughout the world also and the severity of storms along the boundaries increasing. Also this is why Georgia and Alabama may become a no mans land during future summers. Florida in my mind is still hard to figure out. Will it end up being a sand dune or tropical forest.

  2. Prokaryotes says:

    Florida will be flooded.

  3. Prokaryotes says:

    Conservative estimates

    Five feet of seawater to flood Florida’s coastline over the next 100 years, scientists warn http://www.palmbeachpost.com/news/five-feet-of-seawater-to-flood-floridas-coastline-423874.html

  4. Thanks for the heads up on that Joe. FYI we just had the craziest October I have ever seen here in Huntsville AL. Hardly a drop for all of October and then in two days- 5 inches plus.

    Forecasting it every day has been crazy.

  5. Mike says:

    Another victim: http://news.yahoo.com/s/ap/20101028/ap_on_sp_co_ne/fbc_notre_dame_accident

    A strong gust of wind swept across Notre Dame’s practice football field before a tower toppled, killing a student who had been videotaping the team from the tower, the university’s athletic director said Thursday.

  6. Scrooge says:

    I agree the coast of florida is in for dire consequences and so is the govt because of flood insurance. But most of florida is actually more than 5 feet above sea level. I sure wouldn’t buy a house in Miami though.

  7. Dan B says:

    Has anyone done a graphical illustration of extreme weather around the world? It would be very valuable in communicating to people how rapidly the climate is changing and help correlate where agricultural crises are likely to emerge.

    Each of these reports by themselves don’t seem to grab people’s attention unless they’re directly impacted. Victims of floods in Tennessee and Georgia and the 2003 European heat wave are unlikely to link in their minds the flooding in Pakistan and scorching heat in Russia unless there’s a clear visual.

    Changes in the norm and extremes would be a good start. Google, are you listening?

  8. Colorado Bob says:

    Just a reminder of this cycle -

    Six weeks later, Georgia fires still raging

    The state’s inability to keep the fires from rushing out of the Okefenokee Swamp is kindling a debate over lagging forestry budgets.

    http://www.csmonitor.com/2007/0530/p01s01-usgn.html

    http://www.nasaimages.org/luna/servlet/detail/nasaNAS~10~10~73848~179320:Fires-in-Georgia-and-Florida

  9. Peter M says:

    Actually the American south will see a dry/wet tropical savanna by centuries end- that will revert to desert if we do not stop C02 emissions.

    Virgina to NYC will become tropical to sub tropical- with Virginia resembling current day Florida- and NYC Charleston SC.

    Montreal will be like current Philadelphia. All unsettling.

  10. Peter M says:

    I may add that about of one third of Florida will likely have flooding or be submerged.

  11. catman306 says:

    Peter M., have you factored in the hell and high water events into your climate change predictions? Your predictions seem to be best possible cases without thought about the frequent and expectedly chaotic extreme events. Average temperatures only tell part of the story.

    My prediction will be that some locations will have great weather for a few years but that will change to bad. Other areas will have horrible weather for a few years but when the good weather comes much of the ecosystem will have already been destroyed by the bad storms and droughts. After many iterations pretty much everywhere will look like eroded desert with very little large scale vegetation and few trees. Savanna or desert or eroded mountains. The cities will long before have been ruined by mobs of starving looters.

    Agriculture depends foremost on predictable climate.

  12. Mimikatz says:

    Interesting statistical analysis of the Aiguo Dai paper on droughts discussed earlier this week on this site at Early Warning, a kind of eclectic site. If I understand it correctly, he finds that the two things that most correlate with where models predict drought is the prevalence of droughts in the observed past and El Nino Southern Oscillation impacts. The latter explains why the US has gotten off better than the models would have predicted.

  13. Most never take a real hard look at the globe and see that the contiguous states are just a tiny thing wedged between a huge mass of ocean on the west (the Pacific) and another large body of water on the east (the Atlantic).

    These oceans have absorbed most of the excess heat from the greenhouse effect, and their warmer waters will be causing more and more wild and destructive storms and weird weather events.

    Here in southern Illinois we are having the worst drought since record-keeping began in the 1880s.

    I’d like to see the real risk analyses being done by property insurers.

  14. Rabid Doomsayer says:

    Where I live cut off lows provided the rain, as predicted the cut off lows have moved towards the pole. So in the near term we face very dry conditions, getting worse mid term.

    Later we will probably get monsoonal weather and be much wetter.

    So do I move poleward or wait for the monsoon? OK that will not happen within my lifetime.

  15. Peter M says:

    #11 Catman306

    My predictions are a combination of many factors and assorted information I have gleaned from the UCS, and also comparison with the Paleoclimate of the Mid Pliocene which Global temperatures in 2050 are likely to be repeated again.

    I feel storms, erratic weather, droughts, floods are likely to occur as you have said. Climates shifting north from climate change has long been expected- elevation in some localities will naturally change some of the scenarios I have envisioned.

  16. Adam R. says:

    NOAA

    RECORD EVENT REPORT…CORRECTED
    NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
    250 AM CDT THU OCT 28 2010

    …HOTTEST TEMPERATURES FOR SO LATE IN THE SEASON AT HOUSTON
    INTERCONTINENTAL AND HOUSTON/HOBBY…

    A RECORD HIGH TEMPERATURE OF 94 DEGREES WAS SET AT HOUSTON INTERCONTINENTAL ON WEDNESDAY. THIS BREAKS THE OLD RECORD OF 91 DEGREES SET IN 1995. THIS IS ALSO THE HOTTEST TEMPERATURE EVER RECORDED THIS LATE IN THE FALL SEASON AT HOUSTON. PREVIOUSLY…THE LATEST THAT A TEMPERATURE THIS WARM OCCURRED IN HOUSTON WAS ON OCTOBER 19TH…IN 2004.

    THE LOW TEMPERATURE AT HOUSTON INTERCONTINENTAL ON WEDNESDAY WAS ONLY 76 DEGREES. THIS TIES THE RECORD HIGH MINIMUM TEMPERATURE FOR THE DATE LAST SET IN 1939.

    A RECORD HIGH TEMPERATURE OF 92 DEGREES WAS SET AT HOUSTON/HOBBY AIRPORT ON WEDNESDAY. THIS BREAKS THE OLD RECORD OF 90 DEGREES SET IN 1970. THIS IS ALSO THE HOTTEST TEMPERATURE EVER RECORDED THIS LATE IN THE FALL SEASON AT HOBBY. PREVIOUSLY…THE LATEST THAT A TEMPERATURE THIS WARM OCCURRED AT HOBBY WAS OCTOBER 25TH…IN 1942.

    Houston isn’t even in the really hot part of Texas.

  17. Bryan Seigneur says:

    This is the type of work that needs to be done: work that shows the actual lives and dollars lost due to slowing the transition away from fossil fuel. Concentration of precipitation events–droughts interspersed with floods–and overall increases in droughts have a real cost in property damage, lost crop yields, and lives lost. Temperate zone agriculture is most efficient when the rain is frequent and not a deluge. That’s common sense that will help the American people realize that denialists and fossil-protectors are lying to them or deluded.

  18. Richard Brenne says:

    The story about Notre Dame student Declan Sullivan who died on a five-story portable tower videotaping the football team’s practice that Mike (#5) alerts us to is infuriating on many levels. One is that Athletic Director Jack Swarbrick lied to cover Notre Dame’s behind, thinking about money (from a possible lawsuit) instead of the life his organization ended through reckless disregard and criminal negligence.

    Swarbrick said:

    “Things started flying by me that had been stationary for all of practice — Gatorade containers, towels,” Athletic Director Jack Swarbrick recalled Thursday. “I noticed the netting by the goal post start to bend dramatically, and I heard a crash.”

    The Yahoo story continues:

    “Just before the practice began, Sullivan posted Twitter messages in which he said “Gusts of wind up to 60 mph today will be fun at work … I guess I’ve lived long enough.”

    Less than an hour before the accident, he tweeted again, saying it was “terrifying” to be on the tower in the high winds.”

    I’m infuriated because this reminds me that a girl who ski raced at the same time as my daughter was hit by a reckless Vail employee speeding up the mountain during a ski race. I spoke to many parents who were working as gatekeepers all up and down the ski race course and they told me that every time the snowmobiler hit a road traversing the ski slope he was going so fast he caught a lot of air.

    While she was skiing down to warm up before the race in the lane on the slope designated for that, the reckless Vail employee snowmobiler hit the innocent 13-year-old girl when he was in the air and broke most of the bones in her body, killing her instantly.

    Vail immediately put out a press release through their corporate spokesman blaming the girl for being reckless and wearing headphones, something the parents told me was not the case. As an example of an industry closing ranks, the head of the ski patrol at our area chewed out all our ski racers and told them not to be as reckless as the dead girl supposedly had been (and in fact had not been).

    This is what corporations or institutions like Notre Dame and the Catholic Church can easily if not typically become about. The lives of innocent young men, a 13-year-old girl or countless innocent rape victims are not even considered relative to the financial health of the institution, which literally becomes monstrous as a result.

    In other ways each of the three institutions I’m citing here have many other laudable qualities in other areas. Now imagine what coal and oil companies can and typically are like, and you can see the literal monsters we’ve created that appear determined to put their profits and egos before the lives of virtually everyone of every species on Anthro-Earth.

  19. Richard Brenne says:

    Generally the Southeast has seen slightly less dramatic temperature increases than other parts of the U.S. (roughly half of some northern states like New York, Illinois and Washington), leading some to believe they won’t suffer as much as other parts of the U.S.

    But the old cliché that climate change will create “winners and losers” needs to be replaced with the fact that climate change will create “those hit by a truck” and “those hit by a truck and dragged onto railroad tracks then hit by a train that stops to back over them again.”

    According to Climate Central, and re-published in Appendix 1 in Heidi Cullen’s recent book “The Weather of the Future,” Houston will go from averaging 10 95 degree days in July and August 1990 to 45 in 2050, Atlanta will go from 7 to 34, and Tampa Bay will go from 5 to 47 95 degree days in those two months.

    Now imagine the majority of the days in those months with 95 degree highs, an even higher increase in nighttime low temperatures, and the collapse of the grid that provides consistent electricity for air conditioning that Richard Heinberg and many other energy experts predict. (The U.S. would need to invest over a trillion dollars to upgrade America’s infrastructure to the level where China’s will soon be, since they’re spending over ten times the percentage of their GDP on infrastructure, but most American citizens don’t want to pay the taxes to rebuild our crumbling infrastructure, especially those who can most easily afford to contribute.)

    New Orleans, Miami and Tampa Bay are among America’s most vulnerable cities to hurricanes, storm surge and sea level rise, as is the entire Gulf Coast and East Coast, with the danger generally climbing as one goes south.

    Then add malaria and countless other dangers increasing due to climate change.

    And according to Climate Central (again in Cullen’s Appendix 1), every Southeastern state except Georgia has experienced an annual average temperature increase of over 1 degree F (and over 2 degrees during Winter) from 1976 through 2005, with Tennessee having a 1.81 degree F average annual increase and a 4.8 degree Winter increase.

    So the myth of the Southeast not feeling dramatic effects of climate change is comparable to the myth of a justification for slavery or the Confederacy that supported it.

  20. Colorado Bob says:

    Adam -
    Yes , but it’s a wet heat .

  21. Colorado Bob says:

    The Prop 23 people should have paired this in their campaign -

    However, oil interests have a 4-1 advantage on a more obscure ballot measure, Proposition 26, which could also cripple climate action by requiring the legislature to have a two-thirds majority before imposing any new fees or tariffs.

    http://www.guardian.co.uk/world/2010/oct/28/arnold-schwarzenegger-proposition23-oil-climate-change

  22. Adrian says:

    Chicago area, summer, 2010:

    Record-setting 24-hr. rain in July + widespread floods. Record-setting long-duration heat in July. Exceptionally dry September and October. The “Chi-clone.”

    Let’s pause for a moment and remember Nero.

  23. Leif says:

    Another extreme weather event setting up over the North Pacific. A bit early for conformation but fun to watch the progression. Heading right for my diggins.

    http://cliffmass.blogspot.com/