Claim: ‘Megadrought risks in Southwest soar as atmosphere warms’ based on model, ignores records

From Cornell University and the CMIP modeling jockeys comes this claim:

ITHACA, N.Y. – As a consequence of a warming Earth, the risk of a megadrought – one that lasts more than 35 years – in the American Southwest likely will rise from a low chance over the past thousand years to a 20- to 50-percent chance in this century. However, by slashing greenhouse gas emissions, these risks are nearly cut in half, according to a Cornell-led study in Science Advances, Oct. 5.

“Megadroughts are rare events, occurring only once or twice each millennium. In earlier work, we showed that climate change boosts the chances of a megadrought, but in this paper we investigated how cutting fossil fuel emissions reduces this risk,” said lead author Toby Ault, Cornell professor of earth and atmospheric science.

If climate change goes unabated – and causes more than a 2-degree Celsius rise in atmospheric temperature – megadroughts will become very probable, Ault said.

“The increase in risk is not due to any particular change in the dynamic circulation of the atmosphere,” Ault said. “It’s because the projected increase in atmospheric demand for moisture from the land surface will shift the soil moisture balance. If this happens, megadroughts will be far more likely for the next millennium.”

Ault explained a natural “tug-of-war” governing the surface moisture balance between the precipitation supply (rain) and evaporation (transpiration). But he cautions that increases in average regional temperatures could be so dramatic – more than 4 degrees Celsius (7.2 degrees Fahrenheit) – that evaporation wins out. This, in turn, dries out the land surface and makes megadroughts 70- to 99-percent likely.

“We found that megadrought risk depends strongly on temperature, which is somewhat good news,” Ault said. “This means that an aggressive strategy for cutting greenhouse gas emissions could keep regional temperature changes from going beyond about 2 degrees Celsius (3.6 degrees Fahrenheit).”

This lower average warming figure cuts the megadrought risk almost in half, he said.

These tug-of-war scenarios could very well play out in the American Southwest, according to tree ring and geologic records. During sequences of exceptionally dry years, those rings tend to be relatively narrower than in wet years, he said.

“Tree rings from the American Southwest provides evidence of megadroughts, as there are multiple decades when growth is suppressed by dry conditions,” Ault said, pointing to several megadroughts that occurred in North America between 1300 and 1100 B.C.

“We also know they have occurred in other parts of the world, and they have been linked to the demise of several pre-industrial civilizations,” he said.

The tug of war between moisture supply and demand might play out differently in other parts of the world, Ault said.

“Nonetheless, even in the Southwest we found examples of plausible 21st-century climates where precipitation increases, but megadroughts still become more likely,” said Ault, who noted the normally verdant Northeast is in the middle of drought. “This should serve as a cautionary note for areas like the Northeast expecting to see a more-average moisture supply.

“Megadrought risks are still likely to be higher in the future than they were in the past,” he said. “Hence, efficient use of water resources in the drought-stricken American Southwest are likely to help that region thrive during a changing climate.”

“I wouldn’t ever bet against our ability to, under pressure, come up with solutions and ideas for surmounting these challenges,” said co-author Jason Smerdon of Columbia University’s Lamont-Doherty Earth Observatory,” but the sooner we take this seriously and start planning for it, the more options we will have and the fewer serious risks we’ll face.”

###

On the paper, “Relative Impacts of Mitigation, Temperature, and Precipitation on 21st-Century Megadrought Risk in the American Southwest,” Ault is joined by Justin S. Mankin and Benjamin Cook, both of the NASA Goddard Institute for Space Studies, and Smerdon. The National Science Foundation supported this research.

To their credit, they do make the paper available, rather than just expect us to believe the press release.

Abstract

Megadroughts are comparable in severity to the worst droughts of the 20th century, but of much longer duration. A megadrought in the American Southwest would impose unprecedented stress on the limited water resources of the area, making it critical to evaluate future risks under different climate change mitigation scenarios, as well as for different aspects of regional hydroclimate. We find changes in the mean hydroclimate state, rather than its variability, determine megadrought risk in the American Southwest. Estimates of megadrought probabilities based on precipitation alone tend to underestimate risk. Furthermore, business-as-usual emissions of greenhouse gases will drive regional warming and drying, regardless of large precipitation uncertainties. We find regional temperature increases alone push megadrought risk above 70%, 90%, or 99% by the end of the century, even if precipitation increases moderately, does not change, or decreases, respectively. While each possibility is supported by some climate model simulations, the latter is the most common outcome for the American Southwest in Climate Model Intercomparison 5 (CMIP5) generation models. An aggressive reduction in global greenhouse gas emissions cuts megadrought risks nearly in half.

Gosh, if only we could take “agressive” action on GHG’s. The Paper is here: https://cornell.app.box.com/v/megadrought-2016/1/11542178339/96890226850/1

They also provide a video, explaining/pushing the idea…but it was 500 mb in size, on a slow server and I don’t have 45 minutes to wait around to upload to WUWT. You can watch it here if you want:

https://cornell.app.box.com/v/megadrought-2016/1/11540712875

But, megadroughts have been a common feature of the southwest, long before “climate change/global warming” was a glimmer in Jim Hansen’s eye:

For example: Roman Period “megadrought” found in the USA southwest

Certainly, California has experienced megadroughts before. We covered a study that showed they were quite common:

California_drought_timeline

The paper:

North American drought: Reconstructions, causes, and consequences, Cook et al. 2007

PDF here: NADrought

Figure 10 is the source of the above graph:

Cook_etal_2007_fig10

Fig. 10. Long-term aridity changes in the West (A) as measured by the percent area affected by drought (PDSIb−1) each year (B) (redrawn from Cook et al., 2004). The four most significant ( pb0.05) dry and wet epochs since AD 800 are indicated by arrows. The 20th century, up through 2003, is highlighted by the yellow box. The average drought area during that time, and that for the AD 900–1300 interval, are indicated by the thick blue and red lines, respectively. The difference between these two means is highly significant ( pb0.001).

But the most important statement in their study is this one:

Given differences with current radiative forcing it remains uncertain if the Pacific will react in a similar manner in the 21st century…

That’s very true, we just don’t know. Some people claim we’ll see more precipitation and we’ll be in a more El Niño like state rather than La Niña. Just a few months ago we heard this in a story we covered:

Global warming will increase rainfall in some of the world’s driest areas over land, with not only the wet getting wetter but the dry getting wetter as well.

I’ll believe somewhat iffy paleoclimate records over models (especially the poorly skilled CMIP models) any day.

 

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56 thoughts on “Claim: ‘Megadrought risks in Southwest soar as atmosphere warms’ based on model, ignores records

  1. 1) Even the makers of the models admit that they are completely useless for determining regional affects.
    2) Historically, in the US Southwest, droughts have been associated with times of colder than average temperatures.
    3) More CO2 in the air means plants don’t need as much water to survive.

  2. What is …” atmospheric demand for moisture”

    ““It’s because the projected increase in atmospheric demand for moisture from the land surface will shift the soil moisture balance.”

    This sounds rather unscientific to my ear.
    How does the atmosphere demand anything?

    If the humidity is low, water will evaporate until the soil and air are in equilibrium.
    If the air has more moisture than it can hold, it precipitates out.

    • Atmospheric Demand for Moisture is basically this.
      The temperature of an air mass determines how much moisture it can hold.
      When the temperature of the air falls, relative humidity increases. As the Relative Humidity reaches 100%, the Dew Point is reached and moisture condences in the form of Fog or mist.
      Since warmer air can hold more moisture than cooler air, as the air warms, more moisture is drawn from the ground in an effort to stabilize the current relative humidity.

  3. Isn’t it amazing what the models foretell given the conditions in the model and which said conditions never happen or are unrealistic. All the while actual conditions in the real world continue to reveal an inconvenient truth – the models are flawed.

    • Of course you are right. All periods I’ve seen in the past have that were warmer meant more rain and more wet world. Higher temperatures if they were to happen which they aren’t would produce more moisture in the air as much of the surface area of the earth is water. This water doesn’t stay in one place.

  4. Chaco Culture National Historical Park is located in New Mexico. From its history:

    The cohesive Chacoan system began unravelling around 1140, perhaps triggered by an extreme fifty-year drought that began in 1130; chronic climatic instability, including a series of severe droughts, again struck the region between 1250 and 1450.

    I wonder what models say about that time frame.

  5. Thermalization of terrestrial radiation explains why CO2 (or any other gas which does not condense in the atmosphere) has no significant effect on climate. http://globalclimatedrivers2.blogspot.com identifies the three factors which do (98% match with measured, 1895-2015). Blaming CO2 for warming is science incompetence.

    Water vapor has made earth warm enough to be habitable. Water vapor in the atmosphere (measured as TPW (Total Precipitable Water) has been measured by satellite and is reported by NASA/RSS at ftp://ftp.remss.com/vapor/monthly_1deg/tpw_v07r01_198801_201609.time_series.txt (last 2 digits (09) are the month)
    Increasing water vapor is the only significant factor countering the average global temperature decline which would otherwise be occurring. Water vapor is hundreds if not thousands of times more effective at warming the planet than CO2 would be even if effect of CO2 wasn’t made insignificant by thermalization.

    Switching from coal to natural gas adds water vapor increasing the likelihood of flooding.

  6. I don’t give much credence to such studies that draw conclusions for one particular region without showing how it fits in with the whole weather circulation system. There are always floods somewhere and droughts somewhere often at the same time.
    Because this story seems to illustrate how people will find something to support their entrenched views it reminds me of a newspaper report a couple of years ago where Australia’s BOM issued a short range outlook that there was a 40% chance of below average rains in the coming 3 months. The reporter headlined her story a being bad news for farmers who were looking for rain. I called the reporter to make her aware that her 40% below average chance actually meant a 60% above average chance. She simply could not,, and would not, accept what I told her because the BOM had framed the outlook as a below average one and so she was therefore anticipating below average rains even if there was only a 40% chance of it, according to BOM that is.

  7. They should go back to the drawing board and read the definition for ‘drought’ really slowly so that even they can understand it. Drought is ‘below normal’ precipitation that takes place for months to years.

    If an area experiences 35 years of drought, that is climate. That means that region’s climate has changed and the baseline precipitation to declare a drought has decreased.

    Their error in logic here is of course that climate is naturally stagnant, but in reality the exact opposite is true. The western U.S. has had a wetter climate for the past 500 years compared to most of the Holocene. Deserts and semi-deserts covered most of the west all the way to the short grass prairies, which were covered with widespread sand dunes.

    • When I was studying Geology in college 60 years ago we learned that the last few hundred years were wetter than normal in the southwest and that a severe protracted drought was not unlikely, based on the past history. Hopefully now is not the time. But there was no man made CO2 then causing those droughts.

      • Yes, if you can get a drought when CO2 levels are low, you can’t possibly get a drought when CO2 levels are high.

      • Did not say that. Did not mean that. Parts of the West are obviously in a severe drought. The fact that severe droughts occurred without man made CO2 means you can’t blame this drought on man made CO2. They are a natural occurrence in this area

  8. … ignores records …

    This is no surprise whatsoever. The ability to ignore reality is the hallmark of the academic mind.

  9. “We found that megadrought risk depends strongly on temperature, which is somewhat good news,” Ault said. “This means that an aggressive strategy for cutting greenhouse gas emissions could keep regional temperature changes from going beyond about 2 degrees Celsius (3.6 degrees Fahrenheit).”

    No it doesn’t . . the risk of drought being dependent on temps, does not “mean” anything at all about what cutting GHGs might do . . this guy is spewing pretzel logic . .

    • “Tree rings from the American Southwest provides evidence of megadroughts, as there are multiple decades when growth is suppressed by dry conditions,” Ault said,

      Yes, exactly the point I was going to make. Trees on the Yamal peninsula are drought insensitive and are a proxy for temperature. Our trees are special and predict drought.

  10. It is interesting that tree rings indicate precipitation in this study, while others use tree rings for temperature.
    Perhaps tree rings indicate both, plus insects, crowding, fungi, etc., with no real way to sort out which.

    • Of course, Tom. The irony is obvious to us, but not necessarily to a climate scientist. You don’t need to be a botanist to realise that tree growth is dependent on multiple environmental factors. You can make some general statements, like tree rings in desert areas are likely to reflect overall moisture because that’s the limiting factor in their growth. But the only way to separate out individual environmental parameters from tree ring data would be to do a multi-species study over a multi-year period where all the environmental factors are well known from direct historic measurement. Then you MIGHT be able to isolate a way of estimating temperature, rainfall etc. by using something like factor analysis or PCA to tease those data out of another multi-species (the same multi species of course) study where the environmental factors are not known (such as in past centuries).

      Of course, that would be a lot of work, with no guarantee that the results would support your AGW model. So you might not get funding for it.

  11. Totally pseudoscientific Alarmist horsefeathers, based on suppositions and bogus models. Aggressive cutting of GHGs will do nothing but make mankind poorer and less able to adapt and respond to whatever Ma Nature throws at us, including cooling, which is likely.

  12. Use the CESM LENS results to ‘wash’ internal variability. Wrong. A recent post at CE shows the LENS results just prove Lorenz was right and CESM results are exquisitly sensitive to initial conditions. Validating TARs statement that climate is nonlinear (feedbacks) and dynamic (feedbacks are not instantaneous), so mathematically chaotic, so incapable of being accurately modeled.
    Use RCP8.5. Wrong. It is physically impossible. BAU is between RCP4.5 and 6.
    Use CMIP5. Wrong. Already observationally falsified two ways: absence of model projected tropocal troposphere hotspot, sensitivity twice what is observed.
    Regionally downscale CMIP5 to Southwest. Wrong. GCMs well known (many papers) not to downscale well, if at all.
    Ignore historical evidence of past SW US megadroughts (nothing to see at Chaco Canyon?) to make unprecedented future megadrought claim based on quadruply wrong modelling. Demand GHG reduction. Yup, another classic ‘climate science’ paper for the definitive book on warmunist nonsense.

  13. I didn’t know that the Pueblo Indians drove SUVs during the Middle Ages. I have a new found respect for their technical abilities.

  14. Apparently Cornell doesn’t teach math or logic:

    “Megadroughts are rare events, occurring only once or twice each millennium. …,” said lead author Toby Ault, Cornell professor…

    … Ault said, pointing to several megadroughts that occurred in North America between 1300 and 1100 B.C.

    • Ack, I caught about 1 minute of her campaign in Florida today. It is official, Florida is now lost due to extreme flooding, the water level is already a foot higher, hurricanes are on the increase and everybody will be dead.

      In century,
      when these shysters aren’t around any longer, man, that woman screeches something fierce. I sure as heck wouldn’t want to be in an argument with her!.

  15. “An aggressive reduction in global greenhouse gas emissions cuts megadrought risks nearly in half.”

    Apparently not so. Australia was in drought from ~1997-2010. Despite CO2/ greenhouse gases rising during that period Mother Nature won over and the drought broke in 2010. This is despite the prognostications of the Alarmists, probably best illustrated by the then Climate Commissioner Tim Flannery, who said in 2007 that “……. cities such as Brisbane would never again have dam-filling rains, as global warming had caused “a 20 per cent decrease in rainfall in some areas” and made the soil too hot, “so even the rain that falls isn’t actually going to fill our dams and river systems … “. Current Water Capacity for Brisbane is now 100%!

    Some of the people seem to salivate at the most dire predictions they can think of. It reminds me of last week with Hurricane Matthew. They almost seemed to want it to hit and hit hard just so they could say “I told you so but you wouldn’t listen”. It is almost verging on a sickness I fear.

    • These are from Weather Underground. Tides in Georgia are in the range of the maximum storm surge shown here. Depends a lot on when it hits, but it does have a wide shelf, hence the tides. Analysis of this storm will be interesting.

      7.8’ Fort Pulaski, GA
      6.4’ Fernandina Beach, FL
      6.1’ Charleston, SC
      4.5’ Mayport, FL
      4.4’ Springmaid Pier, SC
      4.1’ Wilmington, NC
      2.6’ Beaufort, NC

  16. Persistent, decadal-scale droughts over the western
    United States have been linked to La Niña–like
    SST patterns in the ETP during the instrumental
    period (35). Tree-ring reconstructions extend this
    relationship back to the Medieval Warm Period
    (MWP, A.D. ~900 to 1300), which was seemingly
    characterized by positive solar forcing, inactive
    tropical volcanism, La Niña–like conditions, and
    multidecadal “megadroughts” (3, 5, 6, 35). The first
    high-resolution, continuous Holocene speleothem
    proxy precipitation record from the southwestern
    United States documents a robust connection between
    inferred solar-activity maxima and dry conditions,
    which may be explained by solar forcing of
    La Niña–like states (36). Taken together with our
    SST record, these observations are consistent with
    solar-induced dynamical cooling of the ETP and
    provide predictions for millennial-scale fluctuations
    in the hydrologic balance over the western
    United States during the early Holocene.
    http://instaar.colorado.edu/~marchitt//reprints/tmmscience10.pdf

    • in actual fact
      I think it is the sun overheating and earth trying to protect its population by forming more ozone, peroxides and others TOA;
      but true enough,
      the end result is global cooling
      causing less rain at the higher latitudes
      -statistically speaking-

  17. I don’t know what caused the historic megadrought events (it obliviously has nothing to do with CO2), but there is a simple explanation for Californian droughts in recent years.

    Drought in California = atmospheric blocking caused by the RRR (Ridiculously Resilient Ridge, see Wikipedia) near the West coast of the US. This high air pressure region diverts the storm track from the region resulting lack of precipitation.

    The European heat wave in 2003, and the Russian drought in 2010 were also caused by blocking anticyclones.

    “Warm temperature extremes result from strong adiabatic warming due to downward motion and radiative anomalies in blocking anticyclones. The percentage of blocking-related warm temperature extremes exceeds 80% in large continental regions north of 45°N, and exceeds 60% over the oceans.”
    Source: Shaw et al. 2016: Storm track processes and the opposing influences of climate change (Nature Geoscience)

    It has nothing to do with AGW.

  18. Instead of counting all of the ‘likelys’ and ‘coulds’ in these unverifiable and untestable model scenarios I simply add ‘Of course it also could be as likely as monkeys flying out of our butts. We just don’t know for sure but we need to prepare for the possibility’ to the end of the conclusion. Seems they all have the same ending.

  19. I thought megadroughts in the SW US arise from protracted Negative PDO conditions. Not warmth, but cold?

  20. I would love to see the rain totals for Phoenix, Tucson, and Flagstaff, AZ this year. I know they had record rains earlier in the year. I have seen a lot of rain on the weather map recently, and in the last couple months. Do they just forget about the record rains 6 months prior? (delete them?).

    • Depending on dates selected (cherry-picking, in otherwords) one can arrive at whatever answer wanted.
      Generally this has been a slightly wet year to date for Tucson:

      • “Tree-ring reconstructions extend this
        relationship back to the Medieval Warm Period
        (MWP, A.D. ~900 to 1300), which was seemingly
        characterized by positive solar forcing, inactive
        tropical volcanism, La Niña–like conditions, and
        multidecadal “megadroughts”
        “The influence of solar variability on Earth’s
        climate over centennial to millennial time
        scales is the subject of considerable debate.
        The change in total solar irradiance over recent
        11-year sunspot cycles amounts to <0.1%, but
        greater changes at ultraviolet wavelengths (1)
        may have substantial impacts on stratospheric ozone
        concentrations, thereby altering both stratospheric
        and tropospheric circulation patterns (2). Estimates
        of the secular increase in total irradiance since the
        late 17th century Maunder sunspot minimum
        range from ~0.05 to 0.5% (1). Values in the middle
        of this range are sufficient to force the intermediatecomplexity
        Zebiak-Cane model of El Niño–
        Southern Oscillation (ENSO) dynamics into a more
        El Niño–like state during the Little Ice Age (A.D.
        ~1400 to 1850) (3), a response dubbed the “ocean
        dynamical thermostat” because negative (or positive)
        radiative forcing results in dynamical ocean
        warming (or cooling, respectively) of the eastern
        tropical Pacific (ETP) (4). This model prediction is
        supported by paleoclimatic proxy reconstructions
        over the past millennium."
        http://instaar.colorado.edu/~marchitt//reprints/tmmscience10.pdf

      • “The mid-Holocene (5600–3500 yr
        BP) was a time of consistently weak El Niño activity, as were the
        Early Middle Ages (∼1000–1500 yr BP) and the 19th-to-mid-20th
        centuries. El Niño event strength and frequency were moderate to
        high during the remainder of the last 3500 years.
        Empirical evidence from a diverse set of continuous paleoclimate
        records make clear that the ENSO mode of climate variability
        persisted throughout the last 9200 years, except for the period
        from about 5500–3800 yr BP, when ENSO was weak or inoperative.
        Synchronous changes in Galápagos rainfall extremes and in
        the occurrence of US Great Plains drought with cosmogenic nuclide
        production supports a link between solar activity and ENSO
        throughout most of the Holocene. These observations can be exploited
        to improve models being used to predict changes in ENSO
        caused by anthropogenic climate forcing. Indeed, based on the
        Holocene evolution of ENSO, we propose it is likely that the future
        intensity and frequency of both El Niño and La Niña will be
        at least partly modulated by natural variations in solar activity.”
        http://faculty.washington.edu/jsachs/lab/www/Zhang_Leduc_Sachs-El%20Junco%20Botryo%20dD%20Holocene-EPSL14proofs.pdf

      • ren
        These observations can be exploited to improve models being used to predict changes in ENSO caused by anthropogenic climate forcing. Indeed, based on the Holocene evolution of ENSO, we propose it is likely that the future intensity and frequency of both El Niño and La Niña will at be least partly modulated by natural variations in solar activity

        henry says
        that is also a contradiction…. I find there is no [measurable] man made global warming, hence all climate change aka change in drought/precipitation, is forced by solar activity.
        I know this to be true
        firstly because of my own results on a variety of parameters,
        – indeed the Gleissberg cycle became the only explanation for the results, at 86.5 years exactly –

        but also from measurements by others shows that the Gleissberg is as relevant today as it was during the whole of the holocene
        http://www.nonlin-processes-geophys.net/17/585/2010/npg-17-585-2010.html

        2016-86.5= 1930

        [1932 saw the start of the dust bowl drought]

  21. When it suits their purposes, the AGW soldiers can treat climate as a statistical phenomenon – discussing ‘risks’ and chances – rather than a deterministic phenomenon – CO2 sensitivity, ‘the science is settled’. The reality is that you can’t have it both ways.
    Either you know enough about the many causes and effects to make hard predictions, or you must admit to incomplete knowledge and roll the dice.

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