The Pacific Decadal oscillation, or PDO, is a long-term oscillation in Pacific Ocean temperatures. It is one of several known swings in ocean temperature between two phases, a “cold” phase and a “warm” phase. The most well-known natural oscillation like this is the El Nino-Southern Oscillation, which changes phase every 3-5 years.
The PDO is a longer term oscillation which changes phase every ten to 20 years (hence “decadal”). The graph of the PDO is shown below. If you look on the far right hand side, you will see an uptick or red series of lines in the past few months, indicating that a change in phase from cold to warm may be underway. This could have big consequences for global climate, because scientists think that the cold phase of the PDO has helped keep global temperatures from rising for the last 15-20 years, the so-called “pause” in the warming trend we have seen since the 1970s, If the warm phase returns, it is likely that global temperatures are going to rise again at a faster rate. But since the PDO has only been studied since about 1997, there is a lot climatologists still don’t know about how it will affect climate regionally. It will be interesting to see how this plays out in the next few years.
You can read more about this in this Washington Post article, published earlier this week(link).