Last week I reprised the fact that the current geological age is named for a megadrought:
...If you remember your geologic timescales the divisions of time on
earth run from "eons which split into eras, which break into periods,
which divide into epochs and then all the way down to ages." That's from
Inverse who note the powers that be
decided to call the present age the Meghalayan referring to the
drought-caused worldwide collapse of civilizations 4200 years ago rather
than the much-championed Anthropocene (human influenced) age.
and realized we haven't had a good megadrought post in a while.
Fortunately Physics Today (the membership mag of the American Institute of Physics) had a paper which their blog summarized on August 1. Unraveling the mysteries of megadrought
First though our standard boilerplate on drought in the U.S.:
1) The Great American Desert was called that for a reason. The weather
of the U.S. over the last 150 years is an anomaly in the longer history.
2) The subsidization of row crops, corn in particular, is a political
decision that severely distorts investment and thus nutrition outcomes.
And from Physics Today, "Four ways we know pre-Columbian America was plagued by 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
Roughly the area of 35 000 football fields, Mono Lake, nestled in the
eastern Sierra Nevada, is California’s fourth-largest inland body of
water. Before 1940 it was even larger. That year, the city of Los
Angeles began diverting water from the lake’s influent streams to
provide municipal water. The receding shoreline of Mono Lake exposed two
generations of low-lying tree stumps that had been hidden under the
surface for centuries.
The
diverting of water from the streams that feed Mono Lake in California
has lowered the water level, which in turn has revealed centuries-old
tree stumps that offer clues to the area’s past climate. Credit: Ron
Reiring, CC BY 2.0
In 1994, California State University geographer Scott Stine used
carbon dating to determine that the stump populations were the remains
of trees that had died out around 1100 and 1350, respectively. A simple
ring count suggested that at least some of the trees had lived for half a
century before drowning under rising lake levels. Together, those
pieces of information suggested that twice—once during the late 11th
century and again during the early 13th century—Mono Lake dropped to
exceptionally low levels for periods of 50 years or more. Stine’s study
also yielded evidence of contemporaneous water-level drops in the Osgood
Swamp and West Walker River, near Lake Tahoe, and in Lake Tenaya in
Yosemite National Park. (S. Stine, Nature369, 546, 1994.)
Archaeological artifacts
During protracted water shortages, societies often have no choice but
to alter behavioral habits. During the California drought that lasted
from 2011 to 2017, residents who watered their lawns, washed their cars
with garden hoses, or committed other unnecessary water-related deeds risked being fined.
But archaeological data suggest that those inconveniences pale in
comparison with the disruptions suffered by pre-15th-century Native
American cultures. Archaeologists can deduce those groups’ population
shifts and migration patterns by carbon dating ceramic wares and other
artifacts....MUCH MORE
...Donald Coxe, chief strategist of Harris Investment Management and one
of my favorite analysts, spoke at my recent Strategic Investment
Conference. He shared a statistic that has given me pause for concern as
I watch food prices shoot up all over the world.
North America
has experienced great weather for the last 18 consecutive years, which,
combined with other improvements in agriculture, has resulted in
abundant crops. According to Don, you have to go back 800 years to find a
period of such favorable weather for so long a time.
Well we are now at 26 years of near perfect weather for row crops.
Finally, from March 2015:
That little red blip at the far right side of the timeline is the current drought.
You could make a reasonable argument that for the last 150 years Californians have been living in a fool's paradise.
