The 1997-1998 El Niño versus the 2015-2016 event. How do they differ? How are they similar? The takeaway?
Now that the global HadCRUT4.6 dataset is available for February 2018, it is possible to examine a 4-year period for both El Niños, including the ‘pre’ and ‘post’ months for each.
These two major El Niño events do have some similarities as shown in their respective 4-year charts.
Besides the shared visual pattern of low-to-high-to-low similarity, the peak temperature for both periods came in the month of February (1998 & 2016).
For both, the beginning month (February 1996 and February 2014) were essentially identical: +0.32°C and +0.33°C.
And the end points displayed in the above charts are not dramatically different – there is only a +0.07°C gap between the higher February 2018 anomaly versus that of February 2000.
The small end point difference of only +0.07°C is rather surprising within the context of how much more peak warming took place in February 2016 (+1.11°C) versus February 1998 (+0.76°C).
Then there is a similarity of linear rate of warming for the 24 months leading up to the peak months of February 1998 and February 2016: +22.3°C per century versus +22.6°C, respectively.
Regarding the differences between the two phenomenons:
There is a large difference for the peak month anomaly of the respective Februaries (1998 & 2016). Indeed, a visually striking difference is apparent.
In addition, on average, the monthly anomalies of the 2014-2018 period are +0.35°C then for the 1996-2000 period. Visually, the entire curve for the later El Niño event has been shifted up.
With that said, when the anomalies for the 10-year period prior to February 1996 and February 2014 are compared, one finds that the later anomalies were, on average, +0.3°C higher than those of the earlier 10-year period.
Another difference is the overall warming trends exhibited during the two 4-year analysis periods. From February 1996 through February 2000, the warming rate is +3.6°C per century. The warming rate for the February 2014 through February 2018 is significantly lower at +0.72°C per century.
This substantially larger per century warming rate for the earlier event analysis period – ending in February 2000 – is rather unexpected given the typical mainstream headlines leading up to this last major El Niño.
Then there is the difference in how much the temperature anomaly has dropped since the peak month for each of these El Niños. For the 24-month period after the Feb. 1998 peak, the temperature anomaly dropped a -0.3°C. In contrast, the drop from the Feb. 2016 peak has been double the earlier period’s – a drop of -0.6°C.
Finally, the deceleration of warming rates after the peak highs do differ but not excessively. For the 24-month span ending February 2000, the deceleration of warming from the February 1998 peak was a -18.81°C per century (i.e. cooling per century) versus a deceleration, from the 2016 peak, of -16.44°C per century ending February 2018.
via The Global Warming Policy Forum (GWPF)
April 1, 2018 at 05:55AM