The New York Times: In California, a Wet Era May Be Ending
The drought, now in its fourth year, is by many measures the worst since the state began keeping records of temperature and precipitation in the 1800s. And with a population now close to 39 million and a thirsty, $50 billion agricultural industry, California has been affected more by this drought than by any previous one.
But scientists say that in the more ancient past, California and the Southwest occasionally had even worse droughts — so-called megadroughts — that lasted decades. At least in parts of California, in two cases in the last 1,200 years, these dry spells lingered for up to two centuries.
The new normal, scientists say, may in fact be an old one.
After introducing history the writer starts blabbering about global warming, which is not relevant to historic droughts that resulted in social and cultural changes across the southwest including California. Civilizations rose and then vanished. We live in a region that has experienced extended drought lasting up to 200 years that were not cause by human CO2 emissions.
I have written many times about Scott Stine’s work in the Sierra, especially around Lake Tahoe.
In the 1990s, Scott Stine, a professor at what is now called California State University, East Bay, took advantage of a decline in the levels of Mono Lake and other lakes and streams in the eastern Sierra Nevadas to study tree stumps, still rooted in the ground, that had become visible after having been submerged for hundreds of years.
At some point, water levels must have been low enough for long enough for the trees to grow. By dating the stumps using radioactive carbon techniques and noting their elevations, Dr. Stine was able to reconstruct the ancient water levels and thus the drought history of the area.
The extent of these two droughts has been debated — Dr. Stine says they affected areas well beyond California, but other scientists are not so sure.
“The evidence for the existence of sustained severe droughts is pretty convincing,” said Malcolm Hughes, a scientist at the University of Arizona who corroborated some of Dr. Stine’s work using tree-ring analysis. “But the pattern of how that plays out across the continent is what we’re grappling with.”
If you look at the graphic above you will see that we have been living in a relatively wet period in climate history. A wet period lasting about a 200 to 250 years long. We maybe on the cusp of a much longer drought and our only indicators are history, we have no reliable science for seeing into the future. Stay tuned!