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

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 told NZPA.

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. 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," Dr 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," Dr Renwick said.

2010 one of warmest years on record

This year is almost certainly set to be one of the three warmest years since instrumental climate records in 1850, according to data sources compiled by the World Meteorological Organisation (WMO).

The past decade has also been the warmest 10-year period in recorded history.

The findings were released in the WMO's draft annual statement on the status of global climate today at the United Nations climate conference in Cancun, Mexico.

The statement noted the year began with a El Niño event in the Pacific Ocean, which quickly broken down in the early months of the year. By August La Niña conditions were in place. The report said the event, which is still in progress, is "the strongest since at least the mid-1970s".

A rapid transition took place and La Niña conditions were in place by August.

By some measures the La Niña event in progress in late 2010 is the strongest since at least the mid-1970s.

"The El Niño-to-La Niña transition is similar to that which occurred in 1998, another very warm year, although in 2010 the El Niño was weaker, and the La Niña stronger, than was the case in 1998," it said.

"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."

Dr Brett Mullan, the manager of NIWA's climate variability group, told Science Media Centre the last 16 years contain the 15 warmest years globally in the instrumental record.

"Only one single year of the twentieth century, namely 1998, achieved a global-average temperature higher than the average over the last 10 years, 2001-2010," Mr Mullan said.

"However, the year is not yet over and the current La Nina in the Pacific may yet knock 2010 out of the top slot. Global temperatures inevitably rise in the long-term with increasing greenhouse gas concentrations, but the year-to-year variations are dominated by other factors.

"That large tropical volcanic eruptions cool the global climate is well-known. Climate scientists have also known for more than 20 years that El Niño's influence the global temperatures with a time delay of around six months.

Mr Mullen said the El Niño at the start of the year was a big factor in
predictions last year that this year would be unusually warm.

"Since that time El Niño has dissipated and a very strong La Niña has developed, but we are still to experience the full cooling effect of the latter. So, to me, it is going to be a close call whether the La Niña can pull down global temperatures enough in the remaining month or so of 2010.

"Looking ahead, I would not expect 2011 to be as warm as 2010."