The earth climate is driven by cycles, orbital cycles, solar cycles, ocean cycles and cycles we have yet to identify. However, one of the cycles that has been identified is the Pacific Decadal Oscillation (PDO). The Central Pacific warms and cools on an average 27 year, cycle with longer and shorter periods making up the historical cycle. Scientists do not fully understand what causes the PDO switches, but they are evident in near term climate records and in the historical record take from the Greenland Ice Core.
Below is a graphic of PDO cycles derived from the ice cores, with the measured data in dotted lines on the chart. Note the cool phase from about 1949 to 1977, and then the rapid warming and then a decline. It was this rapid warming that started all the chatter about “global warming” in the press.
It was the cool phase during the 50s, 60s, and early 70s that sparked the coming ice age chatter. Speaking of ice ages, below is a chart of PDO phases during the Little Ice Age.
Why are we discussing PDO cycles? Because cool phases PDOs are associated with droughts in various part of the County, including California, especially when the Atlantic Multidecadal Oscillation (AMO) is in the warm phase. We are currently in a cool PDO phase, with a warm AMO phase. See D. in graphic below. We have been in a warm phase AMO since 1995. Based on the typical duration of the AMO phases, the current warm phase is expected to persist at least until 2015 and possibly as late as 2035. It could be long, long drought.
Historical climate records clearly show the connection between the PDO and AMO phases. If you would like more details in a peer-reviewed study go here: Gregory J. McCabe, Michael A. Palecki, and Julio L. Betancourt, 2004: Pacific and Atlantic Ocean influences on multidecadal drought frequency in the United States. PNAS 2004 101 (12) 4136-4141; published ahead of print March 11, 2004, doi:10.1073/pnas.0306738101
They present the figure below with the title “Impact of AMO, PDO on 20-yr drought frequency (1900-1999)”. The figures correspond to A: Warm PDO, cool AMO; B: Cool PDO, cool AMO; C: Warm PDO, warm AMO and D: Cool PDO, warm AMO
So, what does the future look like? With a Cool PDO and Warm AMO the US temperatures have been flatlining, with no significant increase over the last 15-16 years. With the AMO going into a cool phase between 2015 to 2035 we can expect to see some cooler wetter weather in California. Perhaps I should note that 2020 is about the time that Livingston and Penn predict the sunspots will vanish and we could be in for another Grand Minimum and Cool Phase PDO and AMO.
Here is Don J. Easterbrook, Dept. of Geology, Western Washington University has forecast for the PDO to 2040 based on past PDO history.
Forecasting when the AMO will shift to a cool phase is risky business, but for our analysis let assume about every 30 +/- 5 years there is a shift. 1995 + 30 = 2025, add the plus we have 2030 and minus and we have 2020.
It appears that we are in for some long periods of PDO created drought in California. And, we are could be in some serious trouble, as the states population has doubled since the last water collection dam was built. We can only conserve so much water, then the toilets stop flushing and faucets run dry.