After four years of drought, California’s snowpack levels have already been declared the lowest since records began about a century ago. Now with new information gleaned from tree-ring data, scientists think that California’s snowpack is the lowest it’s been in over 500 years—and maybe even 1000.

Scientists used a new way to measure centuries-old snowpack for the study, which was authored by University of Arizona paleoclimatologists and published in today’s Nature Climate Change. The tree-ring width of 1,500 blue oaks found throughout the Central Valley of the state gave the scientists reliable growth information for about 500 years. When they compared those measurements to tree-ring data since Sierra Nevada snowpack began being instrumentally recorded in the 1930s, the scientists realized that the oaks’ growth accurately recorded the very lowest snowpack seasons. Although it was clear that 2015 had the lowest snowpack levels in 500 years, it’s more likely that it’s the lowest in 1000 years, but these trees just aren’t old enough to show it.

In a story in the New York Times, A. Park Williams, a bioclimatologist at Columbia University commented on the study and added his voice to the growing chorus that climate change has made the drought even worse and noted that low snowpack will be the norm, not the exception:

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“We are now migrating into this new world where temperatures are higher,” Dr. Williams said. “So even though the chances of an event like this were extremely unlikely in the past, in the future it will be more likely to occur.”

Here is the graph from the study which shows the snowpack levels that have been instrumentally recorded from the 1930s to today, followed by the estimates from the past 500 years or so. The red lines are where the instrument-recorded data correlates with the tree-ring estimates. Besides a few potential dips below 2015 levels in the 16th century, this is easily the lowest snowpack measurement scientists have ever seen:

This report comes on the heels of another report from NOAA that the last few years have brought the highest average temperatures in California’s recorded history. Just for fun, let’s check out the graph which shows temperatures since records began being kept in 1895:

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When viewed together those two charts give me chills—El Niño, where are you???

[Nature Climate Change via NY Times]

Peaks in the Sierra Nevada normally covered by snow are almost bare in this April, 2015 photo (AP Photo/Rich Pedroncelli)