Waves Are Getting Taller In North Atlantic

SF Chronicle 20nov00

German scientists have reported that the seas are getting rougher, perhaps because of global warming.

In the latest issue of the journal Nature, H.H. Essen and two colleagues announced there has been a gradual increase in wave heights in the northeast Atlantic in the past few decades.

The team reached this conclusion by analyzing data from seismic stations, which are so sensitive they can monitor pounding waves at sea and on shore.

Essen and his colleagues found that average wave heights in the Norwegian Sea were increasing by about four inches per year in the period between 1955 and 1994. But in the latter part of the same period -- from 1975 to 1994 -- the maximum per year increase in wave height was closer to eight inches.

Also, their records show that in the 1954-1977 period "we detect an average of seven days per month" with strong wave pounding. But "this number increases significantly in the second half of the record, reaching approximately 14 days per month."

Microseismological evidence for a changing wave climate in the northeast Atlantic Ocean

Nature 408, 349 - 352 16nov00

I. GREVEMEYER, R. HERBER & H.-H. ESSEN

One possible consequence of a change in climate over the past several decades is an increase in wave heights, potentially threatening coastal areas as well as the marine industry. But the difficulties in observing wave heights exacerbates a general problem of climate-change detection: inhomogeneities in long-term observational records owing to changes in the instruments or techniques used, which may cause artificial trends. Ground movements with periods of 4–16 seconds, known as microseisms, are associated with ocean waves and coastal surf , and have been recorded continuously since the early days of seismology. Here we use such a 40-year record of wintertime microseisms from Hamburg, Germany, to reconstruct the wave climate in the northeast Atlantic Ocean. For the period 1954–77, we detect an average of seven days per month with strong microseismic activity, without a significant trend. This number increases significantly in the second half of the record, reaching approximately 14 days of strong microseisms per month. The implied increase in northeast Atlantic wave height over the past 20 years parallels increased surface air temperatures and storminess in this region, suggesting a common forcing.