On three separate occasions in the last century, the climate has abruptly changed, affecting salmon stocks and water resources. Ze'ev Gedalof predicts that another abrupt change will happen soon. Smith is one of 14 international researchers examining the ecology and climate signals from high-altitude trees from Alaska to the tip of Chile in a study sponsored by the Interamerican Institute for Global Change Research in Brazil. He used tree rings from mountain hemlock to link the impact of the PDO on land with its impact in the ocean and was able to trace its effects back 400 years. Changes in ocean temperature affect top level predators like salmon by altering the amount of food, like phytoplankton and zooplankton, at the base of the food chain.
Historical records show that temperature changes cause massive reorganizations of salmon stocks.
These changes in ocean temperature also affect the amount of snow which accumulates in the mountains, which has impacts on hydroelectric power generation. During the warm phase of the PDO, competition for water resources for hydroelectric production, fisheries management, and agriculture will be fiercer. The historical data may enable Gedalof to predict how climate will behave in the next decade. The PDO changes states every 23 to 26 years, and the last time it did so was in 1977. That means we are due for another change soon.