Global climate change
Are El Nino Years getting Warmer?
9/25/2015, 6:34:48 PM
Below is the latest up to date NASA GISS plot of the global land/ocean surface temperature anomaly since 1880.
It is looking more and more likely that 2015 will end up as the warmest year on record (currently held by 2014) thanks in part to a strengthening El Nino that is currently in the strong category coupled with a warm (positive) phase of the Pacific Decadal Oscillation (PDO).
It is well known that El Nino has a warming influence on the overall global temperature. A positive PDO also seems to have a warming influence. Based on this and the fact that fourteen of the 15 hottest years on record have all fallen in the first 15 years of this century it is no real surprise that 2015 will likely set another record as underlying warming continues.
What I did below was to first show a globally averaged temperature anomaly graph of just El Nino events going back to the 1950s. The start years of each ENSO event are shown for reference. Basically what I did was average out the monthly, global temperature anomalies (via NASA GISS) that were officially included under EL Nino criteria (via NOAA) whether it was a 4 month period or a 13 month El Nino period. The actual plot of anomalies is labeled in red with the upward trend line in green.
As you can see, it is pretty obvious that El Nino years by themselves are getting progressively warmer over the past 60+ years. Why is that?
A list of EL Nino events in the past 50 years by strength. Typically the stronger the El Nino the stronger the warming influence on overall global temperature.
Next, I made a plot of years where there was an El Nino and a +PDO.
Despite the smaller sample, it is pretty clear once again that years with an El Nino coupled with a +PDO are trending warmer and the most likely reason is the steady increase in greenhouse gas concentration, which is clearly causing an increase in heat which is mostly being absorbed by the oceans. The loss in sea ice in the Arctic is also contributing to the rapid increase in temperature in that region due to a decrease in albedo.
The El Nino Southern Oscillation shows close correlation to global temperatures over the short term. However, it is unable to explain the long term warming trend over the past few decades.
The PDO is an internal process and does not increase or decrease the total energy in the climate system.
Yes, the strong EL Nino and the +PDO are have contributed to the record warmth so far in 2015, but it's not the only story, far from it.
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