Monday, 15 January 2007
Southern California upwelling: Is recent weakening a result of global warming?
Exhibit Hall C (Henry B. Gonzalez Convention Center)
An analysis of southern California coastal upwelling anomalies, sea surface temperatures, surface winds, mean sea level heights and onshore precipitation and stream discharge records for approximately 60 years reveal broad decadal changes, coincident to large-scale shifts in Pacific sea surface temperatures, the PDO. Shorter period variability evident in most records analyzed reflects tropical Pacific influences, ENSO. Additionally, increasing trends in the records may signal a global warming influence. Upwelling anomalies show decreasing values from the mid 1970's to 1997 and correspond to increasing coastal SSTs, higher frequency occurrences of El Niņo (negative ENSO) events, and the positive (warm) phase of PDO. Contrastingly, cooler coastal SSTs and increased upwelling correspond to negative PDO values beginning in 1998. Increased precipitation and stream discharge broadly correlate with mostly positive PDO values and more closely to warmer, shorter-termed El Niņo periods. Since 2002, PDO and ENSO patterns become less discernible in the records. Graphical plots of all variables studied show increasing trends for the years reviewed. These rising tendencies may be the signature of global warming and also demonstrate the interconnectivity of oceanic upwelling, sea surface temperatures, wind speed, etc. For example, increasing trends in meridional wind flow translate, generally, into stronger upwelling and to drier than normal coastal climate. Limited and variable data make proving the global warming connection tenuous. Alternatively, the increasing trends might simply reflect the shift from the negative to positive PDO phase. Overall, climate variability in southern California is predictable from large scale Pacific atmospheric and oceanic patterns. This predictability is useful for long term planning and to establish policy for water and energy resources.