California Coast & Ocean

Sea levels have risen four to eight inches during the past century, largely because of thermal expansion--warmer water occupying a greater volume--rather than as a result of melting glaciers and ice caps, as is commonly assumed. (Ice melt, if we push warming too far, will lead to more ominous sea level rises measured in feet, rather than inches.) The warming happens at the surface, yet slow mixing has been detected as much as 10,000 feet deep, so the entire ocean world is affected. More heat energy in the ocean, as well as in the atmosphere, generates more severe weather. In the last 20 years, researchers at the Scripps Institute of Oceanography, in San Diego, have documented trends of rising storm wave heights, higher incidence of extreme waves, and shorter El Niño cycles. Although an individual extreme-weather event like Hurricane Katrina cannot be absolutely tied to climate change, it is consistent with the patterns predicted by climate change theory and ocean-atmospheric models.

During El Niño years, wind and ocean currents flow west to east in the Pacific Ocean, and warm water collects off the eastern Pacific coast. Jet streams and storm tracks overhead shift accordingly. In between El Niño years, La Niña may appear, when a “cool pool” forms in the Pacific waters closest to us and the currents and wind turn around and flow away from the coast. With El Niño conditions, southern ocean species increase off the central and southern half of California, while northern species of zooplankton and northern cold-water fish decrease within local kelp forests. Green-spotted rockfish (Puffinus griseus) declined by half after the 1970s, while warm-water fish like Garibaldi (Hypsypops rubicundus) increased significantly.

This past winter, the cycle brought us La Niña, and we experienced the coolest winter since the last La Niña, in 2001. Yet the long-term warming trend continued. A National Climatic Data Center report released in March noted that “the combined global land and ocean surface temperature was the 16th-warmest on record for the December 2007-February 2008 period” (0.58¡F above the 20th-century mean). These changes have had profound effects on ocean life.

As carbon dioxide gas dissolves in water, it produces carbonic acid. Ocean water thus becomes more acidic and, coupled with warmer temperatures, kills coral reefs, leaving only bleached-looking white skeletons. Higher acidity also interferes with the formation of carbonate shells of mollusks and other creatures. We collect such shells on the beach, dimly aware that they originally housed living creatures. Microscopic phyto- and zooplankton that encase themselves in carbonate constructions are also damaged. Phytoplankton provide the photosynthetic base that begins ocean food chains, so they are critically important keystone species. Mess with their ability to survive, and the consequences could be widespread and profound.

All this should concern us, but it can be personally difficult to see the connections to ourselves and to grasp that our individual daily greenhouse gas emissions create problems for ocean species that must construct their bodies in sea water that is increasingly acidic because of higher atmospheric carbon dioxide levels.