2012 in global top 10 warmest ever, despite La Nina

[muriel_volestrangler]

Nasa researchers said it was the ninth warmest year while experts from another American agency said it was the 10th.

Both teams said that temperatures would have been higher if it had not been for the La Nina weather pattern that brought cooling to some regions.

They were equally certain carbon dioxide had been the principal driver of the rise over the past 50 years.

The National Oceanic and Atmospheric Administration (Noaa) said that their analysis of temperature data from a global network of weather stations indicated that the average temperature for 2012 was 0.57C above the 20th Century average.

http://www.bbc.co.uk/news/science-environment-21033083

[OnlinePoker]

1. I don't know why they're saying it was a La Nina year

It was La Nina until May (continuing from 2011) and then moved over to El Nino (albeit a weak one) for the remainder of the year. It has gone back into La Nina territory since the beginning of January of this year.

[muriel_volestrangler]

2. They define it as more than 0.5C anomaly for a 3 month running mean

up to that point, with La Nina being -0.5C or below, and El Nino +0.5C above, for at least 5 consecutive months.

So they think there was not an El Nino event in 2012, but there was a La Nina event in the first 3 months of the year.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

So, although the 3 month running mean did peak at +0.6C, since it was only +0.4C in the months either side of it, it's not an official El Nino.

[OnlinePoker]

3. Thank-you for the explanation. n/t