The Declines In Global Temperatures From El Niño To La Niña

I’ve moved to WordPress.  This post can now be found at The Declines In Global Temperatures From El Niño To La Niña

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Global surface temperature and lower troposphere temperature (TLT) anomalies are dropping this year in response to the transition from El Niño to the La Niña conditions in the tropical Pacific. The temperature anomalies in some datasets are dropping more quickly than others, and I was asked to illustrate the typical declines in global temperatures during these transitions.

In this post, I’ve illustrated the drops in surface temperature and TLT anomalies, starting in January and ending in June of the following year:
--For the five years since 1979 when an “official” El Niño event was followed by a La Niña—1983, 1988, 1995, 1998, 2007,
--For 2010 year to date. The most current month is August, with the exception of the Hadley Centre data, which lags and ends in July.
--For the three surface temperature anomaly datasets--GISS, Hadley Centre, and NCDC, and:
--For the two TLT anomaly datasets--RSS and UAH.

Since the January start temperatures are different for each year and for each dataset, I’ve also zeroed the Januarys for each dataset to provide a better visual comparison.

Last, I’ve averaged and compared the surface temperature anomalies, Figure 12, for the years prior to 2010 for each dataset to show how the average declines of surface temperature datasets differ from the TLT anomaly datasets. This was the graph that I was most interested in producing, but there may be those wanting to see the other comparisons, so I’ll present those first.

SURFACE TEMPERATURE DATASETS
Figures 1 through 3 show the land plus sea surface temperature anomalies since 1979, for the transition years from El Niño to La Niña. Year-to-date 2010 data are also included. Illustrated are Hadley Centre, NCDC, and GISS datasets. The GISTEMP dataset is their Land-Ocean Temperature Index (LOTI), which is the combined dataset with 1200km smoothing. All three datasets show elevated temperature anomalies during 2010 with respect to other El Niño to La Niña transition years. (More on that later.) What struck me were the two apparent epochs before and after 1997. That is, if we look at months 3 through 8, the March through August data, there appears to have been an upward shift in the data after the 1997/98 El Niño.
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Figure 1
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Figure 2
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Figure 3
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In Figures 4 through 6, I’ve shifted the datasets so that the January surface temperature anomalies are zero. This should provide for a better visual comparison of the decays in temperatures for those who are interested. The Hadley Centre and NCDC datasets are both showing 2010 as having a slow decline through July and August respectively, but the GISS data is showing a much faster decline, with the 2010 decline now about mid range of the past events.
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Figure 4
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Figure 5
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Figure 6
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LOWER TROPOSPHERE TEMPERATURE DATASETS
Figures 7 and 8 show the UAH and RSS Lower Troposphere Temperature (TLT) anomalies for the El Niño to La Niña transition years. The TLT anomalies in 2010 are closer to 1998 than any other year in both datasets. (More on that later.) If not for the early drop in 2007, it would also appear that there are two epochs in the TLT data, before and after the 1997/98 El Niño.
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Figure 7
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Figure 8
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In Figures 9 and 10, the January TLT anomalies have been zeroed, shifting the data. Unlike the Hadley Centre and NCDC Surface Temperature datasets (Figures 4 and 5), the 2010 TLT anomalies appear to be dropping at rates that leave them mid to low in the range of past events. What really stands out in Figure 9 and 10 is how little the TLT anomalies dropped during 1995.
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Figure 9
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Figure 10
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But as shown in Figure 11, which compares the NINO3.4 SST anomalies for the same years used in this post, the associated 1994/95 El Niño and 1995/96 La Niña events were not very strong in terms of tropical Pacific sea surface temperatures.
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Figure 11

SURFACE TEMPERATURE AND TLT AVERAGES
In Figure 12, the 1983, 1988, 1995, 1998 and 2007 Global land plus sea surface and TLT anomalies for each of the datasets have been averaged. As illustrated, the GISS, Hadley Centre and NCDC surface temperature datasets show gradual declines during the transition from El Niño to La Niña. The RSS and UAH TLT anomaly datasets show slower declines through September, then sharp drops from September to January of the following year.
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Figure 12

WHY ARE 2010 SURFACE TEMPERATURE AND TLT ANOMALIES NEAR RECORD LEVELS?
Refer again to Figures 1 though 3 for the Surface temperature anomaly datasets and Figures 7 and 8 for Lower Troposphere Temperature anomaly datasets. It’s quite obvious that 2010 global temperature anomalies are near to record levels. And if we refer to Figure 11, for the years included in this post, we can see that the January 2010 NINO3.4 SST anomalies were third highest since 1979; that is, the strength of the 2009/10 El Niño was a distant third compared to the 1982/83 and 1997/98 El Niño events. Some might take the elevated 2010 global anomalies as proof of the continued impact of anthropogenic global warming.

In reality, much of this rise in global temperature is, of course, caused by the fact that the East Indian and West Pacific Sea Surface Temperature (SST) anomalies can rise in response to El Niño AND La Niña events and the fact that these warmings can be cumulative when El Niño and La Niña events occur in sequence. I’ve discussed this in numerous posts, including “More Detail On The Multiyear Aftereffects Of ENSO - Part 2 – La Nina Events Recharge The Heat Released By El Nino Events AND... ...During Major Traditional ENSO Events, Warm Water Is Redistributed Via Ocean Currents,” “More Detail On The Multiyear Aftereffects Of ENSO - Part 3 – East Indian & West Pacific Oceans Can Warm In Response To Both El Nino & La Nina Events”, and with animations of numerous datasets in “La Niña Is Not The Opposite Of El Niño – The Videos.”

Also, after fifteen years of relatively flat Sea Surface Temperature anomalies, the South Atlantic SST anomalies shifted upwards in 2009/10. I discussed this shift in the post The 2009/10 Warming Of The South Atlantic, but I still have not found a paper or webpage that presents an anthropogenic cause for it.

And of course, the TLT anomalies of the mid-to-high latitudes of the Northern Hemisphere shifted upwards in response to the 1997/98 El Niño. This was discussed and illustrated with time-series graphs and Hovmoller plots in the post “RSS MSU TLT Time-Latitude Plots...Show Climate Responses That Cannot Be Easily Illustrated With Time-Series Graphs Alone.”

SOURCES
GISS LOTI data:
http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt

Hadley Centre CRUTEM3+HadSST2 data and the HADSST2 data used for the NINO3.4 anomalies are available through the KNMI Climate Explorer:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere

NCDC Land Plus Sea Surface data is available on or about the 3rd of each month through their ERSST.v3b webpage:
ftp://eclipse.ncdc.noaa.gov/pub/ersstv3b/pdo
Specifically for this post:
ftp://eclipse.ncdc.noaa.gov/pub/ersstv3b/pdo/aravg.mon.land_ocean.90S.90N.asc

RSS MSU TLT anomalies:
http://www.remss.com/data/msu/monthly_time_series/RSS_Monthly_MSU_AMSU_Channel_TLT_Anomalies_Land_and_Ocean_v03_2.txt

UAH MSU TLT anomalies:
http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt