Long before sophisticated measuring tools and satellite feeds, it was fishermen off the west coast of Ecuador and Peru who first noticed rising sea temperatures at year’s end.

The God-fearing fishermen named the phenomenon – coinciding with the Christmas period – “El Niño” (the boy).

Usually occurring every three to seven years, El Niño was feared by local fisherman, who could only watch fertile fishing grounds turn barren as warmer sea temperatures kept cold, nutrient-rich deep water from rising to the surface.

While global sea temperatures are now recorded and studied using far more sophisticated techniques, shifts in weather patterns are followed just as closely, particularly by insurers calculating their natural disaster loss reserves and reinsurance limits.

In contrast to South American fisherman, insurers dread the arrival of El Niño’s inverse pattern, “La Niña” (the girl), where warm sea surface temperatures turn cool (measured within a band of just 1.6 degrees Celsius) and cause natural catastrophe costs in Australia to skyrocket.

According to the 2012 JP Morgan/Taylor Fry General Insurance Barometer, which was launched last month in Sydney, the average annual natural catastrophe cost in Australia since 1967 is $1.045 billion.

It says that during “neutral” years – the interim period between El Niño or La Niña patterns before scientists can establish a trend – the average annual cost falls to $816 million.

“In Australia, weather changes can be a significant driver of catastrophe costs,” JP Morgan Insurance Analyst Siddarth Parameswaran says.

“Overall, 2012 estimates for catastrophes were less than what the industry forecast at the start of the year. That seems set to reverse in 2013, based on the early experience to date.”

El Niño weather patterns, generally associated with warmer temperatures and an increased risk of drought and bushfires, signal a reprieve for insurers, with average catastrophe costs of just $490 million, less than half the 46-year average.

But La Niña heralds the opposite. With more rainfall and an increased risk of cyclone formation, insurers on average have paid $3.025 billion each year the La Niña weather pattern was in effect, triple the long-term average and six times higher than El Niño losses.

La Niña, and El Niño for that matter, tend to last for one year. However, statistics from the Bureau of Meteorology indicate Australia has experienced an unusually long La Niña season stretching back to 2007, with the exception of a “moderate” El Niño season in 2009/10.

It would follow that natural catastrophe losses in Australia since 2007 have been above average, and figures from JP Morgan and the Insurance Council of Australia (ICA) confirm this has been the case.

In 2007, 2010 and 2011 insurers paid out $2-4 billion in weather-related claims each year. The last 24 months were officially the wettest on record.

Natural catastrophe losses in 2008 and 2009 were down but still above the rolling 10-year average.

Combined ratios have followed suit. In the worst of the most recent natural catastrophe years, 2011, classes prone to fluctuations caused by weather, namely household and fire & ISR, have been well above 100.

Just two months into 2013, insurers have already paid $674 million in weather-related claims, despite the Bureau of Meteorology’s El Nino-Southern Oscillation indicators in the tropical Pacific remaining at neutral levels for the next nine months.

At present the Predictive Ocean Atmosphere Model for Australia, a Bureau of Meteorology computer model, is predicting a 10% chance of a return to La Niña conditions by September.

Insurers can do little but hope the Girl will stay away.