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La Nina heatwave sweeps the country

Published: 1:58PM Friday December 03, 2010 Source: NZPA/ONE News

New Zealand is in for a long, hot summer as La Nina hits our shores, the National Institute of Water and Atmospheric Research (Niwa) says.

Already, temperatures have soared across the country in late November, a pattern likely to continue until March, principal scientist James Renwick said today.

"In November, pretty much all of the country, the South Island and most of the North Island away from the coast, was quite a bit warmer than normal. Over summer, we're expecting things to be on the warmer side in most places," he said.

He said the current warm weather pattern - along with another La Nina heatwave in the late 80s - was the strongest in about 50 years.

People could expect temperatures to be several degrees Celsius above normal, taking some regions into the 30s "from time to time".

While good news for holiday-makers, it was not so good for Northland or Waikato farmers already concerned about dry conditions, he said.

With little rain forecast before Christmas, Northland farmers facing their third consecutive summer drought this week said they would seek support from the government.

El Nino and La Nina are different stages in a cyclical pattern of climate turbulence in the Pacific.

Tropical cyclone activity is likely to be near - or above-normal - through to May and the risk of an ex-tropical cyclone passing close to New Zealand is slightly above average. Normally at least one ex-tropical cyclone passes within 500 kilometres of New Zealand in the cyclone season.

While El Nino usually brings higher rainfall, La Nina brings cooler sea temperatures, high atmospheric pressure and drier air. Strong winds blow moisture away making for cloudless skies and dry conditions in equatorial countries from the International Date Line east to South America.

"The net result for New Zealand is we tend to get high pressures and more settled conditions," Renwick said.

Some scientists believe that the increased intensity and frequency - now every two to three years - of El Nino and La Nina events in recent decades is due to warmer ocean temperatures resulting from global warming.

"You could say yes, in that temperatures have risen in New Zealand in the last century, so the chances of getting warm conditions have increased... because things are warming up," Renwick said.

The United Nations said today that 2010 is set to be among the top three warmest years since records began in 1850, and the past decade the warmest, in a new sign of man-made climate change.

This year so far was slightly warmer than both 1998 and 2005, the previous top two, but could slip if December is a cool month, the UN's World Meteorological Organisation (WMO) said in a report issued on the sidelines of UN climate talks in Mexico.

"The trend is of very significant warming," WMO head Michel Jarraud told a news conference. Asked if the data were new evidence that emissions of greenhouse gases were warming the climate, he said: "Short answer: yes."

"These are the facts. If nothing is done ... (temperatures) will go up and up."

Antarctic ozone hole smaller

Analysis from Niwa's ozone research shows that the Antarctic ozone hole is smaller this year than any of the previous five years.

Calculations made by combining satellite data with ground-based measurements, including the Antarctica New Zealand Arrival Heights observatory near Scott Base, show that the 2010 Antarctic ozone hole reached a maximum area of approximately 22 million square kilometres and a maximum ozone mass deficit of approximately 27 million tonnes. In 2009 these figures were 24 million square kilometres and 35 million tonnes.

The largest ozone hole ever recorded was in 2000, when it reached approximately 29 million square kilometres and 43 million tonnes deficit.

Niwa's atmospheric experts say the new information adds to a pattern of less severe ozone holes in recent years.

Atmospheric scientist Stephen Wood says the results are encouraging and indicate that international initiatives may now be showing a positive effect on the Antarctic ozone hole.

"We see a lot of year-to-year variation in ozone holes, caused by differences in atmospheric temperature and circulation. So we can't definitively say the ozone hole is improving from one new year of observations. However, we have now had a few years in succession with less severe holes. That is an indication we may be beginning to see a recovery."

Niwa scientists have been measuring surface ozone at the Arrival Heights laboratory near Scott Base since 1988 and measurements taken this year show the lowest levels in Antarctica since the ozone hole first formed nearly 30 years ago.

The Antarctic ozone hole forms in August and September each year, and remains until it is breaks up in November or December. The summer period is when its effects on New Zealand are likely to be largest.