Global Climate: Pacific Decadal Oscillation

The global climate is influenced greatly by the oceans of the Earth. One of the most commonly known ocean conditions that affects climate is the El Nino Southern Oscillation (ENSO), which causes the waters in the southern pacific to fluctuate in temperature. A lesser known condition with similar traits is the Pacific Decadal Oscillation (PDO). The term, coined in 1996 by fisheries scientist Steven Hare, is used to describe notable temperature deviations in the Pacific Ocean, mainly the northern parts off the western coast of the continental US. Location differences are not the only thing that separates the PDO from the ENSO. A normal cycle for the ENSO, whether it is cool or warm, typically lasts from 6-18 months. The PDO however has cycles that can last anywhere from 20- 30 years.

When a cycle is considered "warm" (positive), the ocean temperatures in the northern pacific are cooler than normal, while the temperatures around Alaska and off the west coast of the US are higher than normal. The opposite proves true for a "cool" (negative) cycle.

When regions experience an extreme shift in temperatures, the marine ecosystems usually suffer. Cool phases disrupt growth near Alaska, while warm phases disrupt growth near the western US coast.

It is currently unknown what causes the temperature fluctuation, making climate predictions difficult. The temperatures seem to reflect symmetry over the equator, and the area of water affected is massive. Because of the size of the area affected, small temperature differences can cause large changes in climate, mainly the position of the jet stream over the United States. This has an affect on temperatures and precipitation across the entire country. When there is a cool phase, the jet stream is moved north, causing temperatures to be warmer and shifting the path of potential storm systems. If the underlying cause of this oscillation is discovered, accurate long-range models can be created to predict how the climate will be affected.

Innovative ways of understanding the history and discovering the root of the oscillations are being used today. For example, studying tree rings has allowed paleoclimatologists to study climate fluctuations as far back as the 17^th century. Also, satellites are able to measure water temperatures based on surface height. New studies indicate that the PDO may even consist of two cycle periods. Dr. Yi Chao, an oceanographer at NASA's Jet Propulsion Laboratory, believes that the PDO not only has cycles of 20-30 years, but also those near 70 years. This new theory, as well as the cause of the other cycles will be further tested in the future. Scientists believe studying temperatures below the surface will help provide some evidence as to the cause to these oscillations.

While the cause of the PDO is unknown, the affects are felt across the country. When combined with the right phase of El Nino or La Nina, the PDO can prove to be very troublesome in causing flooding, droughts, and extreme temperatures in the US. Hopefully someday soon the engine of this phenomenon will be discovered, and accurate climate forecasts can be made.

References

Mantua, Nate. January 2000. The Pacific Decadal Oscillation (PDO). http://jisao.washington.edu/pdo/

NASA's Earth Science Enterprise. August 1, 2000. Pacific Decadal Oscillation Packs A One-Two Punch.http://www.jpl.nasa.gov/releases/2000/pdomoodswings.html

NOAA. January 2001. Journal of Climate.NorthClimate.NorthDecadalcific Decadal Climate Variability Since AD 1661. http://www.ncdc.noaa.gov/paleo/pubs/biondi2001/biondi2001.html