While there is a general warming trend in NZ since records have been kept – see the NIWA mean NZ temp graph – El Nino tends to have a downward effect on NZ temperatures as you can see in the global picture. Which means that there is a logical connection to the onset of El Nino and the fact that we had a cold December in NZ. The cold December set the climate change deniers chattering but is not surprising. El Nino also results in warming in the US, which was hotter than usual in December (some places much hotter like New York where they had 20degrees celcius on Jan 6 when they normally have snow on the ground). And Oz tends to have droughts in El Nino.