Life On the Ocean Wave
24 May 2006
GWA Correspondent

So goes the Royal Marines marching song and a catchy number it is but for how much longer mankind will be able to use the seas for his purposes of trade, military expression of power, or simply for pure pleasure is a question that is anything but trivial.

Daily we read of ever larger ships in trouble as conditions get wilder out there. Rising sea temperatures are not just loading up the air with extra moisture but also leading to much stronger surface wind forces. Temperature stress is changing the nature of global meteorology and it seems to have passed largely unnoticed.

In the Fifties a low with a core pressure reading of 970-980 millibars was considered a very severe depression. Look at your old barometers and see for yourselves. Today, we experience winter storms with pressure at their centres going down to 940-950mbs in the higher latitudes (North Atlantic).

At the other end of the scale down near the Equator, the number of hurricanes has increased dramatically over recent years. These are simply tropical depressions with eye pressure readings low enough to generate winds above 74mph (measured 10 metres above sea level). Now we have had to up the scale and categorise a new and even more deadly storm rated as a Major Hurricane. These are defined as having winds if 111mph and above.

The Beaufort Scale, invented in 1805 by Admiral Beaufort himself, found no need to have a number greater than Force 12, which was a hurricane with winds of 74-83 mph. Last year in 2005 there were 7 Major Hurricanes, all off the top of the Beaufort Scale.

The lower the pressure the stronger the winds around the depression will be as the isobars or lines of equal pressure are closer together. If the distance between two isobars is halved from one system to another, the wind force is doubled.

As ever deeper lows develop, whether it be in the tropics or north of Iceland, the isobars will get closer and closer together. The winds generated by such a tight spacing, and the concomitant seas raised, may well make our oceans impossible to navigate safely in the future.

Hurricane Allen had an eye pressure of 899 mbs with winds of 190 mph, while Hurricane Wilma last year had an eye pressure of 888 mbs, the lowest ever recorded.

 

Over the last twenty years there have been claims that super waves as high as 95 ft were being encountered during particularly strong storms. Until very recently these were denied by much of the scientific community, as their models could not replicate them. The existence of these freak waves has now been proven.

 

This week a fifty feet high wave washed over the 41000 tonne Pont Aven, flagship of Brittany Ferries. Sufficient damage was done to force a diversion into Roscoff in France.

 

In the North Atlantic and in the seas off Alaska, fishing has become the world’s most dangerous occupation according to the US Bureau of Labour. At 151 deaths per 100,000 employees it tops the next category, logging, and is three times as dangerous as coal mining. Half of the deaths relate to fishing boats actually sinking.

 

The numbers can only rise as our tempestuous oceans react to climate change.