Anyone following the news this summer knew about California's historic drought -- one guy even decided not to shower for 128 days to raise awareness about water conservation. A new paper published in the journal Geophysical Research Letters shows how unusual such an extreme drought really is. The answer? Very, very rare.
In fact, the 2012-2014 California drought is the worst drought in the region in the last 1,200 years (at least), and the project's researchers Daniel Griffin and Kevin J. Anchukaitis figured this out using tree cores.
The Guardian's Dana Nuccitelli reports:
The study used drought reconstructions from tree-ring cores, from the North American Drought Atlas (NADA) and from cores Griffin & Anchukaitis collected from blue oak trees in southern and central California. Blue oak tree ring widths are particularly sensitive to moisture changes. According to Griffin, "California's old blue oaks are as close to nature's rain gauges as we get."
The study compared today's drought conditions in California to those reconstructed over the past 1,200 years using the Palmer Drought Severity Index (PDSI), an estimate of available soil moisture.
They concluded that not only was this drought the worst in over a millennium, but that it was the worst because of record heat.
"Temperature could have exacerbated the 2014 drought by approximately 36 percent," Griffin and Anchukaitis wrote. "These observations from the paleoclimate record suggest that high temperatures have combined with the low but not yet exceptional precipitation deficits to create the worst short-term drought of the last millennium for the state of California ... Future severe droughts are expected to be in part driven by the anthropogenic influences and temperatures outside the range of the last millennium."
However, the exact cause of the drought is the subject of controversy. Another more recent study conducted by the National Oceanic and Atmospheric Administration disputes that causal linkage. Instead, the researchers argue that the drought was caused by a lack of precipitation caused by natural atmospheric cycles -- not climate change. In an interview with Mother Jones, oceanographer and lead author Richard Seager said, "The preponderance of evidence is that the events of the last three winters were the product of natural variability."
Still, others have called the NOAA study "deeply flawed" for misinterpreting ocean and Arctic sea ice data, according to NBC News, and for largely ignoring extreme temperatures in the state.
While the science of climate change is not controversial (and will affect droughts in the future), the science of this particular drought is still undetermined. NOAA meteorologist Marty Hoerling spoke of the second paper: "This is by no means a final analysis, or a final word, about the California drought."