On a misty Sunday morning in Wellington...

...there have to be better things to do than debate climate change.

But, hey, I plead the XKCD defence.

So here we go.

Unafraid of waking the neighbours on a Sunday morning, Poneke has a post up loudly declaring the global temperatures stopped rising in 1998; and claiming that this fact devastates the case for anthropogenic global warming.

Okey dokey.

Here's my reply (repasted here so my links make it past Poneke's spam filter).

Gosh, I’m hardly awake myself and all of a sudden my pager is blurting noise. Mullah Gore has detected some climate change denial in my quadrant and it’s up to me to silence it. I tell you the hours in this job are lousy. Good thing I am a zealot.

Poneke,

On any given day or any given year numerous factors contribute to global temperature. We are worried about human Greenhouse Gas (GHGs) emissions because they are very likely to lead to a trend of increased temperatures globally*. Such a trend will not be a perfectly linear increase because GHG’s are only one contributing factor to temperature. Amongst this signal we’ll see plenty of noise. The noise which caught your ear this morning is, for the most part, a product from the El Nino/La Nina cycle you talk about. 1998 was an exceptionally hot year because of the powerful El Nino effect that year.

In the Hadley Centre dataset 1998 was the hottest year since records began. In NASA’s dataset 2005 was. In both datasets, if you eyeball a graph of averaged temperatures, this means you’ll see a ‘dip’ or plateau in temperatures this millennium. However, in either dataset, if you place in trend lines the trend (the signal without the noise) is still one of warming.

You will also notice, if you look at a graph of temperature trends since 1975, that there have been two other similar dips. And then the rise continues.

Now, if our ‘dip’ continues for another 10 years, then we’ll have reason to believe that there is something missing in our understanding of the globe’s climate. But until then it simply isn’t accurate to claim that global warming has stopped.

Oh, and no one in the World Meteorological Association is going to be called a denier for the simple reason that the don’t deny anthropogenic climate change. From Reuters:

OSLO (Reuters) - Climate change is still nudging up temperatures in the long term even though the warmest year was back in 1998 and 2008 has begun with unusual weather such as a cool Pacific and Baghdad’s first snow in memory, experts said.

“Global warming has not stopped,” said Amir Delju, senior scientific coordinator of the World Meteorological Organization’s (WMO) climate program.

Last year was among the six warmest years since records began in the 1850s and the British Met Office said last week that 2008 will be the coolest year since 2000, partly because of a La Nina event that cuts water temperatures in the Pacific.

“We are in a minor La Nina period which shows a little cooling in the Pacific Ocean,” Delju told Reuters. “The decade from 1998 to 2007 is the warmest on record and the whole trend is still continuing.”

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*And remember here, that global means global. Temperatures in specific locations may perform quite differently.