After a hiatus of nearly 30 years, changes in wind patterns may bring warm surface waters back to the West Coast of North America. Warmer waters might be a relief to swimmers, but they would also bring rising sea levels, which can damage coastal communities.
"There are indications that this is what might be happening right now," study researcher Peter Bromirski of the University of California at San Diego's Scripps Institution of Oceanography said in a statement.
Bromirski's team studied the amount of force that wind has been putting on the surface waters of the Pacific Ocean, a contributor to the Pacific Oscillation patterns. Off the West coast this wind moves the surface water of the ocean, and pulls up the deeper, colder water layers — called the "positive" phase. The wind has the opposite effect near the equator.
When the cycle shifts to the "negative" phase, the wind causes downwelling, so less cold, dense water gets brought to the surface of the Pacific Ocean. The resulting warmer surface water will expand more than the cool water, raising the sea level.
The researchers found that current winds over the Pacific are similar to the conditions of the 1980s. The last negative phase took place during that decade, when sea-level rise on the Pacific coast was similar to that elsewhere in the world. The last positive conditions prior to this period ended in 1946.
The current change in wind patterns may foreshadow a shift to this negative phase, which could return sea-level rise to near — or possibly even higher than — the global rate.
Around the globe, sea levels are rising. During the 20th century, they rose at a rate of about 2 millimeters (0.08 inches) per year, which increased in the1990s to 3 millimeters (0.12 inches), an uptick frequently linked to global warming.
These rising sea levels could impact coastal development, beach erosion and wetland water levels. Higher sea levels damage coastal communities and beaches, especially during coincident high tides, storm surges, extreme wave conditions and violent El Niño/La Niña seasonal conditions.
The study will be published in a forthcoming issue of the Journal of Geophysical Research-Oceans.