Global Warming? Blame it on El Niño

Somehow it’s already that time of year again… November. Bam, its Christmas! Oxford Street lights have been switched on, Mariah Carey will soon be wailing out of every speaker, and what everyone is desperate to see, (don’t fret, there’s not long to wait) the 2015 John Lewis Christmas advert.

So, as tradition says, you have to buy your nearest and dearest presents. But what to get that person who has everything? I have the answer. This: 

Source: Designed by Words & Unwords for Zazzle.com   

If you’re not feeling the t-shirt, not to worry, you can get the same design on a mug, tote, or for that really special person, how about a badge?

Stylish and educational, don’t you think?  

The results of a study (McLean et al., 2009) stated that at least 68% of the variance in global tropospheric temperature anomalies (GTTA) is accounted for by the Southern Oscillation Index (SOI), i.e. ENSO. This raises to 81% accountability in the tropics.

They are some large percentages. So maybe the t-shirt isn’t being sarcastic after all?

“The close relationship between ENSO and global temperature, as described in the paper, leaves little room for any warming driven by human carbon dioxide emissions.”

This is a quote taken from the press release related to the paper by one of the authors, R. M. Carter.

Hmm, now I’m really hoping the t-shirt is, as I first thought, being sarcastic.

So how did McLean et al come to such a bold conclusion? Well, essentially by removing the long term upward trend of the global tropospheric temperature anomalies. This trend can be seen by the GTTA line in Figure 1.



Figure 1: Twelve-month running means of SOI (dark line) and MSU GTTA (light line) for the period 1980 to 2006 with major periods of volcanic activity indicated

Source: McLean et al., 2009

A mere -0.223 correlation is found between the pre-transformed variables, suggesting a very weak negative correlation. However, when both the SOI and GTTA data is transformed into time derivatives, a correlation of -0.847 is found. This is now suggesting a very strong negative correlation, and thus forms the basis for the study’s conclusion. However, these time derivatives are calculated by subtracting the 12 month moving average from the same average for data 12 months later. It is said this transformation is to remove noise, but this herein lies the problem, as it removes the linear upward trend of the temperature data. Therefore a strong correlation will be found, as it has been recognised that El Niño has a strong effect on short term global temperatures but that it cannot account for the long term trend (Santer et al. 2001, Lean and Rind 2008, Foster and Rahmstorf 2011).

In fact, in direct contrast to McLean et al., 2009, it has been suggested that El Niño has had a slight net cooling effect on global temperatures (Fawcett, 2007). This has also been noticed for the period 1979 to 2005 by Lean and Rind, 2008, and for the period 1979 to 2010 by Foster and Rahmstorf, 2011.

I hope we are now all in agreement that global warming is not the fault of El Niño? Please drop me a comment if you have any questions.

Finally, if you do decide to buy the t-shirt for someone this Christmas, hopefully you’ll now have enough knowledge to share over your turkey (or vegetarian equivalent) dinner.