Upper-ocean warming is changing the global wave climate, making waves stronger

When wind impacts the ocean it puts its energy into both increasing height and horizontal velocity. Geologists and coastal engineers have long been interested in this transfer of energy, as one example movement of sediment along shorelines. Old physics books say that cold air is denser so higher temperatures might allow higher wave heights, all other things being equal, which in the ocean never are. Then again colder, denser air should move more energy into waves. There is also the complication of swells from distances and origins past and the state of the sea surface from fetch, and surfactants for example, pour oil on the sea.

When did temperature first appear in such formulas? I would be more interested in changes in cold and warm front frequency. Density of air is important but so is that of the ocean.

Have not seen the paper but if they are so smart let them harvest the energy from waves. Old idea, easily fails. Doubt if the authors have been to sea much. At the same wind speed I always felt safer at higher temperatures but those were times of old history.

Why am I skeptical that anyone can say what the total “global wave energy” is right now, let alone back in 1946? Or any year in between?
And why are waves bad?

Let’s look at some first principle reasoning.

Wave power (wave height) is a combination of wind field speed and Reynolds number of the fluid as the wind field pushes across the fluid surface.

Reynolds number (Re) is inversely related to kinematic viscosity. Kinematic viscosity is the ratio of dynamic viscosity over density. Thus decreasing kinematic viscosity (or dynamic viscosity) will increase Re. Increasing Re will create higher waves for the same wind speed. However, the scientific/engineering question is, “Is the effect measurable within uncertainty for the temperature changes under question?”

Sea water (at 36 g/L salinity) dynamic viscosity is slightly temperature dependent. Empirical tables tells us that moving from from 29 deg C to 30 deg C (warming) decreases dynamic viscosity from 0.00088 Ns/m^2 to 0.00086 Ns/m^2, a ~2.5% decrease/deg C. But seawater density also decreases with temp, but not nearly as fast, about 0.5%/deg C. Thus kinematic viscosity decreases about 2%/deg C in the range of SST temps of interest (20-30 deg C).

So as SST rises also Re rises. A 1 deg C rise in SST will increase Re by about 2%. So at most, Re has increased less than 2%, as global SST rise has been slightly less than 1 deg C since 1948. With an uncertainty of probably at least 5% in WP change, I doubt a 2% change has any significance out of a noisy measurement.

(for NOAA’s global SST changes, see this chart:

Note: the scale on that chart is in Fahrenheit.)

Now compare this to the statement made by Dr. Borja G. Reguero:
“In fact, wave power has increased globally by 0.4 percent per year since 1948, and this increase is correlated with the increasing sea-surface temperatures, both globally and by ocean regions,…”

The energy from wind is what generates waves of course to make Wave Power (WP). But for every climate model simulation that projects a wind energy increase to 2050 or 2100, you can find one that predicts an oceanic winds decrease. Thus wind speed changes of the ocean under CC is very uncertain. So what does history tell us?

Historically we know the oceanic trade winds strengthen during periods of global cooling like 1940-1970, and winds weakened as from 1910-1940, a period when global surface air temps increased by about 0.4 deg C.

So over much of the period under study, 1948 to today, trade winds increased to about 1977 and diminished somewhat to 2000. Since 2000, trade winds have been strengthening, suggesting an on-going deep ocean cooling cycle (and that gave us the Pause). (Note: the direction of causality is difficult because trade winds and SST are coupled processes. That is more wind speed increases the more deep water overturning occurs, and deep water overturning brings colder water to the surface thus cooling the climate).

However every climatologist is in general agreement that weaker trade winds will accelerate climate change warming as oceanic surface-deepwater overturning is decreased. This will keep more warmth in the upper layer of the seas and thereby warming the surface air temps. So for a climateer to suggests ocean Wave Power will increase as ocean wind field speeds diminish under CC is simply spewing nonsense.

As far as storms go for generating waves, the IPCC reports are quite uncertain about stronger storms over the oceans. Most honest climatologists will tell you that as the temperature gradient between the tropics and the poles decrease under CC, then storm strength will lessen. The dishonest climatologist of course always predicts more intense storms under CC regardless of the physics under consideration.

So in those 70 years since 1948, this climateer is claiming wave power increased by 28%. I find that hugely unlikely due to an SST effect on Re, but merely a likely result of oceanic wind speed increase during the Pause since ~2000. And oceanic winds speeds (thus WP) will increase as the SST cooling proceeds to a return us to the Pause (hiatus) state in the coming years. And the observed increase in WP since 2000 will likely revert back to the mean under a warming/diminishing wind speed cycle sometime after 2030-2035.

And in any case, the climateers say that oceanic wind speeds will diminish under CC global warming as oceanic overturning decreases. So Borja G. Reguero’s claim on Wave Power and warming under CC is hogwash by both first principle and by even the climateers’ own dogma concerning CC effects on ocean winds.