I was an ocean engineering major at the Naval Academy. I wasn't an outstanding student by any measure, but I got the degree.
There are things that stuck with me, one of them is "wave power varies as the cube of the height." That is, a wave that is twice as tall has eight times as much power.
Energy is the capacity to do work. Power is the rate at which work is done.
Most ocean waves are wind-generated, and wave height varies linearly with wind velocity. That is, a 10% increase in wind speed yields 10% higher average wave heights.
Wind speed is a function of energy in the atmosphere, temperature and pressure differences in various regions of the atmosphere. A warmer atmosphere has more energy, and so larger differences can occur, although on a global scale one might think that the average atmospheric temperature is equally greater, so the differences that drive wind would be relatively the same. But, it's complicated and they're not.
The analysis revealed that in the era beginning after 1970, California's average winter wave height has increased by 13% or about 0.3 meters (one foot) compared to average winter wave height between 1931 and 1969. Bromirski also found that between 1996 and 2016 there were about twice as many storm events that produced waves greater than four meters (13 feet) in height along the California coast compared to the two decades spanning 1949 to 1969.
So (average winter Pacific northwest) wave heights have increased 13% since 1970. That means average wave power has increased 1.13^3, or ~1.44. That's 44%!
That's 44% more power to erode shorelines, move sand. In a rising ocean.
Shoreline erosion is taking place at a much faster rate than it has in the past. We can quibble about whether it's 20%, 30%, or 44%, but no matter what number you want to put on it, you have less time to "manage" shoreline erosion.
We have to move faster.
Originally posted at Notes From the Underground 09:55 Monday, 7 August 2023