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Report on the Health of the World's Oceans (6)

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Climate Change

Besides overuse and mismanagement, and pollution from land and sea, there is yet another factor influencing the health of the world's oceans. This final impact may be the most devastating, and the least understood. It seems harmless, but can wreck havoc on our oceans, and land. This final impact is simply, climate change. Often cited as "global warming" and attributed to increased levels of CO2 and other so-called "greenhouse gasses", the causes and effects are not that clear. Sometimes we come to a dilemma in studying the complex factors contributing to our climate. It may be hard to determine which is the cause and which is the effect. It's much like the saying, "Which came first, the chicken, or the egg?"

The strange weather that has been observed in recent years, and the apparently changing weather patterns may be from a combination of factors. One factor is known as the Pacific Decadal Oscillation (PDO). Periodically Pacific Ocean temperatures tend to switch from one temperature extreme to another. Scientists believe that we may have experienced such a switch starting a year and a half to two years ago (21). If this was a true shift, it should last 20 to 30 more years (21). The shift is characterized by a swath of warmer than normal water from Japan eastward, 2/3 of the way across the ocean (21). At the same time, unusually colder water remains in the rest of the North Pacific (21).

A possible effect of a switch in the PDO would be an increase in salmon in Washington and Oregon, while Alaska salmon dwindle (22). Other marine species may experience similar changes in location and abundance.

A similar temperature switch happens periodically in the Atlantic Ocean, and is known at the North Atlantic Oscillation (NAO) (23). In one state of this shift, called the "high" phase, there are strong storms near Iceland, and warm air over northern Europe, while in the alternative phase, storms are weak over Iceland, and northern Europe is colder (23). Environmental variations played a role in failed fisheries in Iceland in the 17th through the 19th centuries (24). It may be possible that during this time a shift in the NAO occurred that contributed to the fishing conditions. Other factors are just as likely, and it's not well understood exactly what was the cause (24).

The last phase of the NAO starting in 1976, and possibly ending in 1999 may have caused drought and winds in Africa (31). These winds carried dust and a soil fungus that killed more than 90 percent of a soft coral known as sea fans in the Caribbean (31). The same winds caused decreases in Diadema sea urchins (31). Sea urchins graze on algae that grow on Staghorn coral (31). The resulting increase in algae from lack of urchins killed large numbers of Staghorn coral (31). Other epidemics known as "coral plague" coincide with years of high dust load (31).