ENSO influence on temperature variations

Here's an interesting chart I just put together - it's a plot of 12 month averages of the Southern Oscillation Index and de-trended RSS temperatures. It's interesting to note how close the ups and downs match up except for the Chichon and Pinatubo eruptions which are marked.

So, when skeptics like to make hay about temps have flattened or dropped since 2003 (or whenever) notice what the SO index was doing. Then consider that we just entered ENSO neutral conditions (neither EL Nino or La Nina) after being in a La Nina and may enter El Nino conditions soon (May's SO index was -5.1 which would be 5.1 on the chart) - so what will the temps do then?

Now, before the skeptics get all excited and try to say "see - its ENSO and not CO2 driving temps" I'll point out that the RSS data has had the trend of about 0.0013 C removed per month (0.0013 for the 1st month, 0.0026 for the second month, etc up to about 0.4684 removed for April 2009). The ENSO data is unaltered because it has no trend (Dave - that means it's "flat"). So the correlation we are seeing here is correlation with the wiggles in the trend, but not correlation with the trend.



I didn't do anything fancy here, it was very simple:
- Reverse the sign of the SO index so that El Nino conditions are positive and La Nina conditions are negative.
- Calculate the per-month slope of the RSS data and subtracted that times the months from the start from the RSS data. This removes the trend from the RSS data so what we have is the variation from the trend (Dave - that makes it "flat").
- Average every 12 month span (01/1979 to 12/1979, 02/1979 to 02/1980 etc)

The ENSO data is from here:
ftp://ftp.bom.gov.au/anon/home/ncc/www/sco/soi/soiplaintext.html
With a brief explanation here:
http://www.bom.gov.au/climate/glossary/soi.shtml

The RSS data is here:
http://www.remss.com/data/msu/monthly_time_series/RSS_Monthly_MSU_AMSU_Channel_TLT_Anomalies_Land_and_Ocean_v03_2.txt

I would not count on El Nino just yet ...

Here is a corroborative report that suggests the current flat trend in global temperatures will remain flat for another decade until 2020:

http://news.bbc.co.uk/2/hi/science/nature/7376301.stm

I've also noticed strong correlation between global temperature with the Pacific Decadal Oscillation (PDO), which suggests no temperature increase likely over the next two decades before entering a warming phase around 2030.

In either case, one thing's for certain if temperatures fail to rise in the next 10 years: the AGW debate will get hotter!

An interesting document to read is

Impact of global warming on enso variability using the coupled giss GCM/ZC model
EICHLER Timothy; RIND, David; ZEBIAK, Stephen

Abstract
This study uses a hybrid coupled model (referred to as the general-circulation model (GCM)/Zebiak/Cane (ZC) model), which consists of the Goddard Institute for Space Studies' (GISS) Atmospheric general-circulation model (AGCM) coupled to the oceanic component of the ZC intermediate model to assess the impact of global warming on El Niño behavior, with and without the influence of heat introduced from the subtropical Pacific (via subtropical cell (STC) pathway). The baseline GCM/ZC model produces El Niño variability with a two year periodicity and an amplitude of approximately half the magnitude of observed El Niño. The GCM/ZC model also produces an appropriate atmospheric global response to El Niño/southern oscillation (ENSO) as shown by composites of 500 hPa heights, sea-level pressure (SLP), 200 hPa wind, and precipitation during El Niño and La Niña periods. To evaluate the importance of global warming on ENSO variability, 2x CO2 and 4x CO2 transient simulations were done increasing the atmospheric CO2 one percent per year, then extending the runs for an additional 70 years to obtain equilibrium climates for each run. An additional set of global-warming simulations was run after including a STC parameterization generated by computing 5-year running means of the sea-surface temperature (SST) difference between a transient run and the 1 x CO2 GCM/ZC run at the anticipated subduction zones (160-130°W, 20-40°N and 20-44°S, 160-130°W) and adding it to the base of the equatorial mixed-layer of the ZC model with a time lag of 15 years. This effectively alters the vertical temperature gradient of the ZC model, which affects SST via upwelling. Two features of the GCM/ZC response to global warming are emphasized. Firstly, the inclusion of the STC results in a major redistribution of heat across the equatorial Pacific, leading to an El Niño-like response in the final equilibrium solution with less variability about the mean. The global warming aspect due to the El Niño-like response results in a positive feedback on global warming, which causes a higher global surface-air temperature (SAT) than identical transient simulations without inclusion of the STC. Secondly, including the STC effect produces a far greater magnitude of global ENSO-like impact because of the reduction of, or even the reversal of, the equatorial Pacific longitudinal SST gradient. The implications of such an extreme climate scenario are discussed.

International journal of climatology ISSN 0899-8418
2006, vol. 26, no10, pp. 1283-1314


El Niño and climate change
Trenberth, K. E. and Timothy J. Hoar
National Center for Atmospheric Research, Boulder, Colorado
Geophys. Res. Lett., 24(23), 3057–3060.

A comprehensive statistical analysis of how an index of the Southern Oscillation changed from 1882 to 1995 was given by Trenberth and Hoar [1996], with a focus on the unusual nature of the 1990–1995 El Niño‐Southern Oscillation (ENSO) warm event in the context of an observed trend for more El Niño and fewer La Niña events after the late 1970s. The conclusions of that study have been challenged by two studies which deal with only the part of our results pertaining to the length of runs of anomalies of one sign in the Southern Oscillation Index. They therefore neglect the essence of Trenberth and Hoar, which focussed on the magnitude of anomalies for certain periods and showed that anomalies during both the post‐1976 and 1990‐mid‐1995 periods were highly unlikely given the previous record. With updated data through mid 1997, we have performed additional tests using a regression model with autoregressive‐moving average (ARMA) errors that simultaneously estimates the appropriate ARMA model to fit the data and assesses the statistical significance of how unusual the two periods of interest are. The mean SOI for the post‐1976 period is statistically different from the overall mean at <0.05% and so is the 1990‐mid‐1995 period. The recent evolution of ENSO, with a major new El Niño event underway in 1997, reinforces the evidence that the tendency for more El Niño and fewer La Niña events since the late 1970s is highly unusual and very unlikely to be accounted for solely by natural variability.

Are interesting papers to read concerning the effects of ENSO on global warming. Based on a quick google scholar search these papers reflect current uncertainty whether ENSO affects global warming or global warming affects the ENSO. I just love science