Warm and wet weather... blame the blob

By SIMON COLLINS science reporter

Scientists have found an extraordinary "warm blob" in the oceans around New Zealand that sent temperatures soaring to record levels in the late 1990s.

The blob, from north of New Zealand northwest to the Solomon Islands, raised the average sea level about 5cm above normal.

It raised the average temperature in the top 800m below the surface of the Tasman Sea by 1.2C - producing extra heat equivalent to between 5000 and 10,000 times New Zealand's daily use of electricity.

Dr Philip Sutton, of the National Institute of Water and Atmospheric Research (Niwa), said it was the biggest change observed in the heat system.

"We are very excited about it because it's a huge signal and it could well happen again."

He told a climate change seminar organised by the Foundation for Research, Science and Technology in Wellington yesterday that the Tasman started to warm in 1996, peaked in 2001 and was now cooling.

This was not the result of long-term global warming, but was associated with an unusually strong swing in the weather pattern in the Pacific in 1998, when an El Nino pattern bringing cold, dry weather to much of New Zealand switched suddenly to a La Nina, bringing warm, wet weather.

"We think the wind fields in the central Pacific created a nice warm pool of water.

"We don't really understand how it got down to New Zealand."

The country's average temperature soared from 12.3C in 1997 to 13.4C in both 1998 and 1999 - the hottest years since records began in the 1860s.

Temperatures have since dropped back to 12.6C last year, in line with the average of the past 30 years.

Dr Sutton said the "warm blob" in the surrounding oceans showed up as an anomaly in satellite measurements since 1993, which recorded a global average rise in sea level of just under 3mm a year.

"Around New Zealand it's more like 10 to 15mm a year. It's quite an amazing feature.

"Warm water is lighter and therefore stands taller."

The warm sea temperatures were confirmed by measuring devices dropped overboard from container ships plying between Auckland and Suva, Lautoka (Fiji) and Brisbane, and Sydney and Wellington, under a collaborative deal with research institutes in Australia and the United States.