Temperature Variation Due to ENSO

In this post I use the Multivariate ENSO Index (MEI) supplied by NOAA at http://www.esrl.noaa.gov/psd/enso/mei/index.html and lower tropospheric temperature data supplied by UAH to show how much of temperature variation over the past 20 years is due to ENSO and how little is due to CO2.  I will keep words brief and let graphics do the talking.

Firstly, here is the MEI data from 1950:

Fig. 1:  Monthly MEI from 1950

As an aside, this is how it compares with SOI data.  The SOI is inverted and both are scaled for comparison.

Fig. 2:  MEI compared with SOI inverted

Now compare scaled MEI with Global UAH:

Fig. 3: MEI (scaled) and UAH

Notice tropospheric temperatures appear to lag the MEI by some 5 months:

Fig. 4: MEI advanced 5 months and UAH

Notice both datasets are noisy, and there is a clear discrepancy in the early 1990s.  12 month running means show this more clearly:

Fig. 5:  12 month means of UAH and MEI advanced 5 months:

The slump in UAH data is shown by the arrow.  Mt Pinatubo’s main eruption was in June 1991. (Without El Chichon in 1982, there may well have been a much higher spike in the mid-1980s).

Now let’s look at the correlation between monthly MEI and UAH.  Firstly, the whole period from December 1978:

Fig. 6:  UAH vs MEI advanced 5 months 1978 – 2016

About 13% of temperature variation is associated with MEI variation.  Doesn’t tell us much does it.  What if we exclude the UAH data for two years from April 1982, and from July 1991 to December 1995?

Fig. 7:  UAH vs MEI advanced 5 months 1978 – 2016 with periods after volcanic eruptions excluded

Considering the fluctuations in both datasets, that shows a fairly strong correlation.

Next, we examine the periods, before, during, and after the Pinatubo influence.

Fig. 8:  :  UAH vs MEI advanced 5 months December 1978 – June 1991, excluding April 1982 to March 1984

Again we see a similar correlation.

Fig. 9:  UAH vs MEI advanced 5 months July 1991 – December 1995

The strong positive correlation of the previous plots has broken down.

Fig. 10:  UAH vs MEI advanced 5 months January 1996 – June 2016

The correlation is even higher.  Over half of temperature variation is associated with ENSO variation five months previously.  Here is the same 1996-2016 plot but with 12 month running means:

Fig. 11  UAH vs MEI advanced 5 months January 1996 – June 2016, with 12 month running means

74% of temperature variation for the past 20 years and 6 months can be explained by previous ENSO variation alone.  In the same period, carbon dioxide concentration at Mauna Loa has increased by 44.77 ppm, which is more than 49% of the entire increase from 1958, and Global temperature as measured by UAH has increased by a little over 0.1 degree C.

No wonder Global Warming Enthusiasts were pinning their hopes on the 2015-16 El Nino to put an end to the Pause, but they must also hope for the ENSO- temperature correlation to break down shortly, as a deep La Nina will mean cooler temperatures and further embarrassment for them.  However, the correlation breaks down when volcanoes cause lower temperatures in El Nino conditions as we have seen, but what mechanism could there be for higher temperatures in La Nina conditions?  Perhaps that magical greenhouse gas CO2?  That would indeed be spectacular- there are no outliers at the low end of any of the above plots.  The most UAH has been higher than expected with low MEI is about +0.2C to +0.3C, and those values cannot be described as outliers.  Besides, UAH for June is already down to +0.34C, and we are only four months past the peak- the cooling has barely begun.

Finally, this is a plot of the centred 37 month mean MEI (because La Ninas can last for three years).

Fig. 12: 37 month centred mean MEI

Notice that before 1975 the 37 month average never exceeded +0.5, the majority of the time was in negative territory, and in the 1950s and 1970s reached below -1.0.  Since 1975 the MEI has dropped below -0.5 only once in 2000 and approached -0.5 in 2012, but has been in positive territory for the vast majority of the time, exceeded +0.5 in six events, and was above +1.0 in the early 1990s.  It would be surprising if global temperatures had not seen a large increase.

How low will the monthly MEI go with the coming La Nina, and how low will the following global temperatures go?  All depends on La Nina’s length and strength, but the monthly MEI data are falling fast.  Stand by.

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The Pause Update: June 2016

The complete UAH v6.0 data for June were released yesterday.  I present all the graphs for various regions, and as well summaries for easier comparison.  The Pause still refuses to go away, despite all expectations.

These graphs show the furthest back one can go to show a zero or negative trend (less than 0.1 +/-0.1C per 100 years) in lower tropospheric temperatures. I calculate 12 month running means to remove the small possibility of seasonal autocorrelation in the monthly anomalies. Note: The satellite record commences in December 1978- now 37 years and 7 months long- 451 months. 12 month running means commence in November 1979. The y-axes in the graphs below are at December 1978, so the vertical gridlines denote Decembers. The final plotted points are June 2016.

 [CLICK ON IMAGES TO ENLARGE]

Globe:

The 12 month mean to June 2016 remains at +0.46C and should stay at about this value for the next two months.  If so, The Pause, (now 1 month shorter), will continue to be an embarrassing reality! However, it may end soon after with a small positive trend.

And, for the special benefit of those who think that I am deliberately fudging data by using 12 month running means, here is the plot of monthly anomalies, which shows that The Pause is over by my rather strict criterion:

+0.3C/100 years since December 1997- not exactly alarming.  The Pause will return sooner with monthly anomalies than 12 month means of course.

Northern Hemisphere:

The Northern Hemisphere Pause has ended as expected.  Note the not very alarming warming of 0.21 +/- 0.1C per 100 years for half the record compared with 1.37C for the whole period.

Southern Hemisphere:

The Pause has shortened by 2 months.  For well over half the record the Southern Hemisphere has zero trend.

Tropics:

The Pause has shortened by another 3 months with the El Nino influence, but is still over half the record.

Tropical Oceans:

The Pause has shortened by another 2 years- the El Nino now having a strong effect on the 12 month means.

Northern Extra Tropics:

The Pause by this criterion has ended in this region, however note that the slope since 1998 is +0.29 +/- 0.1C per 100 years compared with +1.59C for the whole period.  That’s still embarassingly slow warming.

Southern Extra Tropics:

The Pause has lengthened by another month.

Northern Polar:

The Pause has decreased by 1 month.

Southern Polar:

The South Polar region has been cooling for the entire record.

USA 49 States:

No change.

Australia:

The Australian Pause has not changed.

The next graphs summarise the above plots. First, a graph of the relative length of The Pause in the various regions:

Note that the Pause has ended by my criteria in the Northern Extra Tropics and the Northern Hemisphere, but apart from the North Polar region, all other regions have a Pause of 18 years 8 months or longer- well over half the record, including the South Polar region which has been cooling for the whole record.

The variation in the linear trend for the whole record, 1978 to the present:

Note the decrease in trends from North Polar to South Polar.

And the variation in the linear trend since June 1998, which is about halfway between the global low point of December 1997 and the peak in December 1998:

The only region to show strong warming for this period (18 years 1 month) is the North Polar region: the Northern Extra Tropics, Tropics, and the Northern Hemisphere have very mild warming but all other regions (including the Globe as a whole and all of the Southern Hemisphere) are Paused or cooling. The imbalance between the two hemispheres is obvious. The lower troposphere over Australia has been strongly cooling for more than 18 years.

12 month means will continue to grow in some regions for the next few months, so the Pause as here defined may end in some regions shortly (probably North Polar, Tropics, and Tropical Oceans), and may not reappear until early 2018.  The impact of the coming La Nina will be worth watching.  Unless temperatures reset at a new, higher level and continue rising, very low trends will remain.