Pre-Columbian America was plagued by decades-long megadroughts

In the August issue of Physics Today, climate scientists Toby Ault and Scott St. George share a pair of startling research findings. Between roughly 800 and 1500 CE, the American West suffered a succession of decades-long droughts, much longer than anything we’ve endured in modern history. And statistical models suggest that, as the climate warms, such megadroughts are increasingly likely to return.

The western US was plagued by multiple decades-long droughts, data from tree rings reveal. Credit: Greg Stasiewicz. Data from the North American Drought Atlas.

How can scientists be so sure about the duration and extent of droughts that happened long before the era of instrument-based precipitation records? As Ault and St. George explain, the annual growth rings of ancient trees contain a rich paleoclimatic record of precipitation and soil moisture patterns. The width of a tree ring gives clues as to how well nourished the tree was in a given year. The map shows four western US megadroughts predicted from tree-ring data.

Ring-width analyses provide the most complete set of data on past moisture levels. But researchers have other ways of determining those conditions. Here are four of them:

  • Underwater tree stumps
  • Archaeological artifacts
  • Sand-dune cores
  • Pollen-grain deposits

Full story here

h/t to WUWT reader “Theo”



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Dr. Bob

And I thought tree rings only predicted temperature!

Bryan A

An interesting pattern though…

808-842=34 years drought
842-976=134 years wet

976-1010=36 years drought
1010-1126=116 years wet

1126-1160=34 years drought
1160-1264=104 years wet

1264-1298=34 years drought

Donald Kasper

Except that the areas of drought are very different each time.

Bryan A

Actually all have fallen on Utah with gradual subsequent expansion into Nevada, then Wyoming, and then to include Montana and Southern California.


Yeah, there’s a whole field for that–dildoclimatology or something like that.

Ian Magness

Good one! 🙂

Old England

We know that trees grow faster in higher CO2 levels and require Less water – but there is no definitive way to relate growth seen in tree rings to any one of 4 key variables .

Temperature – although the ambient temperature is not the key factor some choose to suppose because numerous studies have found and demonstrated that trees can and do control, and moderate, leaf temperature to optimise photosynthesis regardless of the ambient temperature.

Sunlight – without data on cloud cover and thickness the amount of solar energy available for photosynthesis and thus Growth is an unknown variable

Precipitation is another factor affecting growth – but growth is then moderated by the other factors of temp, sunlight, soil conditions and CO2 levels, and that’s before you consider it’s position in relation to other trees. Again we know that too dry and too wet soil will reduce growth and cause stunting.

CO2, the basic feedstock of plant and tree growth. Without accurate knowledge of CO2 levels, and there aren’t, there is no way of determining what amount of growth or lack if growth can be attributed there.

Dendrochronology seems to allow any conclusion that the ‘researcher’ wants to be drawn from tree rings. Seems like that ‘discipline’ is perfect for climate ‘scientists’

Ian Magness

And to that, OE, you can add changing soil thickness and nutrition and short- and long-term attack by parasites and disease. In short, as you imply, it is very difficult (if not wildly speculative) to attribute change in tree ring growth over time to any single factor.


Lake levels, tho, are pretty good indicators of precip. For ex, there’s solid evidence that Lake Tahoe’s level has been much lower (underwater stumps).

John Brisbin

Liebig’s law of the minimum dictates that the most scarce critical resource controls growth.
Light, water, CO2, mineral nutrients, organic nutrients….
Rings only tell you that these things change in their availability, not which one did in a particular case.

Always interesting how they try to prove things with data that when actually examined absolutely disproves their hypothesis.

The best tree-ring reconstructions do show a slightly higher temperature (+0.1C) than the 1904 – 1980 mean for North America. From just before 800 CE to around 1075 CE. ( After that, the tree-ring studies show a lower temperature right up to the modern day (even when you include the hockey stick producing tricks). Between -0.1C and -0.3C lower for the majority of that period.

Long-term North American temperatures have very little (I would say none) correlation with long-term drought conditions. Without correlation, there is not even the faintest possibility of causation; you can throw away your obviously false hypothesis without a qualm.

Yet, here these fools are; they can’t even make up a plausible lie.

Donald Kasper

Tree rings don’t record temperature. They record moisture. That is 80 years of research saying that, and yes, they did understand the concept of temperature at the turn of the 20th century.


Trees are lousy thermometers, but pretty good hygrometers.


I would really like to see the research that supposes to correlate temperature with growth alone, as growth is the only thing that tree rings demonstrate. There are lots of reasons why a tree might be doing well one year vs. another. Perhaps all its neighbors were cut down.


@ rocketscientist:
You are going to *love* the Finnish “Supra-Long” chronology.
Here is a detailed presentation showing the hard work of obtaining samples, and then the meticulous work getting a temperature calibration.
Do check it out, it is truly remarkable.

Steve McIntyre covered it in two posts over at Climate Audit, very favorably.
Here is his second post, note that it contains a link to his first post (up top).

Science done right.

Thank you for the correction. I should have said something like “…for those who believe that tree rings correspond solely to temperature…”

Any way you look at it – no correlation, unwarranted “scientific” conclusion.

Todd Pedlar


John Bell

Too much hyphen-abuse in that list, but an interesting topic and story. Imagine of all things, droughts in deserts.

Donald Kasper

The whole of the southern Rocky Mountains is included in that area. That is not desert.


Nor is Sacramento, CA.

Alexander Carpenter

Were you to live there, you would not claim that. Most people don’t consider California to be a desert, either, yet most of it is exactly that, certainly off monsoon-season.


I lived in the Bay Area for four years and San Diego County for two.

If a desert be defined by less than eight inches of rainfall, then most of CA is not a desert. Much of it is semi-arid.

Average precipitation at Sacto is 18.52 inches, so even in droughts, it doesn’t qualify as desert.

Here is CA precip:

The floor of the southern San Joaquin Valley and most of SE CA is indeed desert. The rest, not so much.



First, no h/t for the Physics Today article; now under moderation.

What gives?


No worries. Thanks for explanation.

Ron Long

I remember when an underwater camera filmed tree stumps and indigenous stone rings 90 feet below the current level of Lake Tahoe. Caused quite an alarm as regards drought potential.


I would venture to guess that there are quite a few more inhabitants of the Lake Tahoe area now as well.

Bruce Cobb

“And statistical models suggest that, as the climate warms, such megadroughts are increasingly likely to return.”
Bingo, there’s the Alarmist, money-grubbing turd stuck into what is otherwise some interesting research.

Donald Kasper

There are two camps. Camp one, with a history of over 80 years publications states that tree rings record only rainfall noticeably. Camp two, arising in the 1990 timeframe ignores that 80 year history and reports that tree rings only report temperature noticeably. You cannot unravel moisture and temperature together in tree rings. Apparently this is still undecided which one they record. I will stick with rainfall.


Tree rings measure the water uptake and growing season of trees. Maybe also CO2 in the air. If it’s hot, more water will evaporate. Since trees get their water via the ground, their uptake is a function both of temperature and precipitation, but mainly the latter. Average temperature does vary over the centuries of tree’s life, but not by all that much, unless it survived across a glacial-interglacial transition.

D. J. Hawkins

Not only that, but many tree species have an ideal ambient temperature for growth. On either side, growth slows down.


I believe that’s true of other parameters, as well.

Donald Kasper

Tree rings are based on: moisture, days above freezing, timing of last snow melt, amount of cloudiness and coastal fog, soil nutrients, sun exposure/blockage by other trees, root damage, daily and seasonal amount of time in shade (reducing water demand), insect pest injury, slope orientation, altitude, soil maturity, species, tree water demand, forest floor albedo (plants vs rocks), groundwater migration, plant in relation to forest canopy top/access to sun, proximity to water ponding and springs, root development, lightning damage, glaze and snow damage, to name a few. So dendrochronologists never said there was an absolute indication of rainfall amount, just a general concept of wetter or drier. Trees at the White Mountains, CA bristlecone pine for plants like alpha-one are on south facing slopes only. The north facing slope pines are totally different growth, more robust and round. Nearby ancient sage have to be chopped up to count rings as the growth is very erratic and lobate in appearance. So for those, it depends on what lobe or orientation of a lobe you pick. The problems using trees are basically endless with none of the parameters able to be constrained. From this, we then got a residual signature using spooky statistics developed by the researchers to look for certain periodicities of temperature, that is temperatures of certain time scales. Really, what temperature are trees supposed to record? Daily/weekly/monthly/seasonal average minima? Maxima? Mean? Someone needs to cut the propaganda and explain what climatic temperature they are talking about, but of course, the can’t and don’t. Sort of a bs fog on what temperature is supposed to mean for trees.


Donald writes

Camp two, arising in the 1990 timeframe ignores that 80 year history and reports that tree rings only report temperature noticeably.

Actually the “temperature measuring tree rings” are selected from areas thought to be limited by temperature to make temperature the most significant factor. For example at the tree line on a mountain.

That doesn’t rule out other factors like moisture, it just allows them to justify what they’re doing. Which is still a crock in scientific terms. Even more so when post-hoc selection is used. No matter how they try to justify it afterwards…

Donald Kasper

The idea of temperature was from a paper on something like Norwegian coastal pines comparing summer and winter rings where the summer ring is wider when warmer, but defined only on long term temperature of 100 years or more. They did not ever read a ring to say a temperature, it was a very long term average. This then became any tree on earth recording temperature. Again, what a ring for a year means in terms of any climate metric of temperature has never been defined. Trees are not neutral indicators of climate. They are preferentially affected by extreme weather. My paper in the 80’s proved, for example, there is no correlation of tree deformation growth to the climatic mean annual wind. When a sorry climatologist out of Japan studied Tokyo bay and showed the trees always leaning perpendicular away from the coast he concluded that the winds of Tokyo came in and diverged. I explained that salt degrades growth toward the source oriented to the ocean, and whatever the coastal wind was doing, the tree will grow perpendicular to the shoreline. This is not the shore mean annual wind direction. It is a very restricted component of the climate that disproportionately damaged the trees. In any alpine system, the main effect on trees is snow and glaze damage from winter storms, and the amount of time they are in snow. The trees are not going to start growing until the snow is gone and temperatures are above freezing all day. This is a freeze response not a direct daily temperature response. Longer snow coverage and the growing season is shorter and the rings are thinner.

Donald Kasper

For that paper, if you have a southern Sierra extreme cold spell with short summers, the rings are going to be thinner, and these people are going to report “drought”. This is sloppy.

Donald Kasper

They drill core the wood in the SW adobe structures to date them, and get a rainfall record at the same time.


Don’t the dates 800-1500 CE overlap or coincide with the Medieval Warm Period, ca 950-1250?


Many paleoclimatologists consider the MWP to have run from c. AD 950 to 1400, and the LIA from c. 1400 to 1850. But others favor different start and end dates.

Some other conventional dates are for the Roman Warm Period, 250 BC to AD 400, and the Dark Ages Cool Period, 400 to 950, but with slop on both ends of each.

The cycles might be shortening, which is not a good sign, if you like it warmer rather than cooler.


Not only is the length shortening, but the peak temperature of each warm period is decreasing.


Yes, indeed. Noticeably and worryingly.

Maybe humans will be able to warm the planet enough so that the Modern WP can just beat out the Medieval, slowing the inevitable downtrend in place for at least 3000 years, but probably 5000, since the end of the HCO.


Megadroughts in the American Southwest during that time are well known. The time coincided broadly with the Medieval Warm Period. One such severe drought is believed responsible for the disappearance of the Anasazi Indians. They built the iconic cliff pueblos which contain an abundance of tree logs spanning a range of centuries. The logs provide a wealth of information for both dating and climate.
Nothing surprising or new about any of this.

Donald Kasper

The Anasazi did not disappear. They migrated down to the rivers to farm.


You mean that the Aztecs didn’t eat them?

Shouldn’t higher global temperatures drive higher precipitation worldwide, with considerable local and regional variation? With the wet regions remaining the same, getting wetter, or getting dryer, and the dry ones remaining the same, getting dryer, or getting wetter, as, of course, not only does the precipitation change in a region, but also the boundaries between these regions shift.

It looks like here we have a great example of complexity not amenable to disambiguation (is that really a word?) by old-paradigm, Modern and post-Modern reductionist linearizing science. No wonder the paper itself seems so dodgy, trying to squeeze prior-concludings from mixed data.


There is a potential for temperature changes to shift weather patterns. Rain would continue to fall in the same amounts. Just in different places.

NOTE: I said potential. Nothing has been proven, and models are not proof of anything.


If CO2 is the control knob, then the required higher water content should produce more precipitation, right?

“Climate Change” = politicians covering up Planet X, or Ninbaru. You can bet they and the super-rich already have their underground shelters safe from the teeming hordes.

Pop Piasa

Then again there’s also the threat of Planet Z, or Nincompoop.
You can bet there’s no surviving a planetary collision, above or below the crust of the planet.
I’m curious… How do “teeming hordes” relate to the topic of this thread?

Pop Piasa

Really far out there, predicting drought during this little “age of aquarius”, while warm SSTs are pumping moisture into the dry extremes of polar latitude, limiting their winter heat loss through cloud cover.

Gary Pearse

So the thickness of the tree rings are now indicative of water or lack thereof- the same data that gave us the temperature hockey stick! How do they know it wasnt cold weather instead of hot drought. This is the only science that uses the same data to divine each of two mutually incompatible conditions. Oh and whatever happened to high CO2 making plants resistant to drought.

The chaotic system here is the minds of climate alarmists, not climate . The two strange attractors are marxbrother тоталiтагуaиs and the CO2 putsch.


We don’t know what caused them, but we know that CO2 will bring them back.

This isn’t science, it’s mysticism.


Looks like coincidental dates with the disappearance of the Anasazi. They supposedly disappeared around 1300 CE. The last drought did them in.

Roger Bournival

Were the tree rings in the study gluten free?


In the inimitable words of Sam Kinison … when the next super mega hyper drought blankets the Western US and turns it into a desert … Move. MOOVE!!!! MOOOooovvvVVVVEeeeee!!!!!!

It’s kinda how man has survived the fickle “moods” of Mother Nature

Walter Sobchak

I miss him.

Alan Tomalty

There are some droughts that have lasted a 1000 years.

“The sediment cores from Valles Caldera go back 550,000 years and show evidence of megadroughts that lasted as long as 1000 years during the mid-Pleistocene Epoch during which summer rains were almost non-existent.”


This suggests that drought can prevail for much longer periods. The evidence seems good although I don’t know if their theory of causation is solid or just based on coincidence but the basic idea is that the monsoons shift north and south based on Earth’s axial procession. The drought that creates the Sahara desert, and the desert belt that stretches east from there will, according to this theory, persist for another 15,000 years. Then the Sahara has the chance of once again becoming the very wet, green place it was 6000 to 9000 years ago.
When The Sahara Desert Was Green


And the Nevada Triassic ichthyosaurs

Shoki Kaneda

This pre-Columbian artifact was recently found and explains many past climate phenomena. Our knuckle-dragging ancestors had Suburbans!
comment image?version=0


It’s a woodie.


Is academia trying to make CE=AD? Even the PRC uses AD, and they are real communists.

F. Leghorn

It bothers me too


We have better than tree ring data in Australia that says something similar.

The coral of the great barrier reef gives us a very good picture of run off from at least coastal Queensland, by the amount of sediment deposited on the reef by major rivers.

Cores taken from the reef in the 1960 can be easily read to give the rainfall patterns from before white settlement by comparison the sediment deposited by known rainfall events today.

Those cores indicate that when the renowned Captain Cook was making his voyager of discovery up the east coast in 1770 Queensland was just recovering from a 28 year old drought, all of which was as severe as our current drought, just 5 times longer than anything since.

If the same occurs again you can bet there will be much slandering of that much maligned innocent molecule, CO2.


Aridzona prone to drought? Who would have thought…

But wait a minute…I thought tree rings were a proxy for temperature. Isn’t that what Mann used? Now they’re a proxy for precipitation?

A Multi-purpose proxy that can be used to demonstrate whatever it is you want to demonstrate…how convenient.

By the way…Who was driving the SUV’s and using the fossil fuel generated electricity that caused the mega droughts back in Pre-Columbian times?

I mean…if the only possible cause for any mega droughts we have in the future is humanity killing the planet, that must be what caused it before, right? Couldn’t possibly be natural climate variations, could it?

We already knew the past history of droughts – ask the Anasazi . The American Southwest has been in a drought condition of one sort or another for a long long time, and it repeatedly gets decades of really dry weather. Nice to know that they acknowledge that this is not new.


There is also evidence of Hyper-El Ninos in South America in the per-Colombian period. Entire cities that depended on fishing were abandoned because there were no fish in the warmer waters. In addition the warmer moister air hit the Andes which wrung out the excess moisture to produce massive flooding. Musta been CO2 though, Mann can’t be wrong.

Tom Schaefer

Isn’t there grass colony organisms that are tens of millennia old? Would there be a way to use those to extend this analysis back even further with genetic analysis or carbon dating? What about sediment layers? More rain = more sediment. Have they tried taking cores from the Salton Sea bottom, maybe deeper cores from San Francisco bay?


This research, which was reported earlier in 2018 in the Journal of Climate, is attempting to turn the tables on honest science by claiming that results from fraudulent GCMs should really be regarded as data which should be used to make decisions about the future. The authors also discount and devalue historical data because it represents only one state (even though the honest/truthful state) and models are capable of cranking out way more outcomes to consider than the historical record. The senior author of this so-called research, Ault, I think has played too many video games.

Big Rich

CE? Are these people total pagans? WTV?


So we had mega droughts pre CO2 blaming.

Could we make an argument that the Climate changes with or without CO2?


CO2 follows climate changes. It doesn’t cause them.


The magical tree rings again.

Steven Zell

The droughts indicated in blue and yellow (through eastern Nevada and Utah) correspond to the Medieval Warm Period, while the wider drought area in red corresponds to the cooling near the end of the Medieval Warm Period near the end of the 13th century. So which was worse for the people living in the American west during those times–the warming in the 10th through 12th centuries, or the cooling during the late 13th century? If the latter, we could infer that a cooling climate causes worse droughts in this area than a warming climate.


In general, cooler is indeed drier.