New Kid in Town

El Niño (“the little boy”) is the warm phase of an ocean/atmosphere oscillation; it helps heat go from the ocean to the atmosphere and warm up our weather. During its counterpart, la Niña (“the little girl”), it does the opposite, moving heat from the atmosphere into the oceans. The whole phenomenon is called the El Niño southern oscillation, or ENSO, but it often happens that we just say El Niño for the whole thing.

It’s one of the things that affects Earth’s global temperature — temporarily — and there are lots of ways to quantify it, i.e. to “put a number on it.” One of the best is MEI, the Multivariate El Niño Index. It’s the way I describe El Niño when I adjust global temperature for temporary factors (volcanic eruptions, solar variations, and yes, El Niño).

There’s a new kid in town, or at least, a new way to quantify El Niño. The scientists who constructed MEI have come up with a new, improved version (version 2), so of course I’ve re-computed the adjustments based on the new version of MEI data. Since the new version covers the year 1979 to the present, that’s the time span for which I’ve computed adjusted data.

Let’s start with the global temperature data before we try to remove the influence of temporary factors. Here it is (monthly averages, the whole globe, since 1979, from NASA):

My estimate is that the whole el Niño thing had this much effect on global temperature during this time:

We can see the warm spikes from the big el Niño events of 1998 and 2016. But there’s an even bigger one in 1983, even though that didn’t show up as a super-hot year like 1998 and 2016 did.

That’s because there are other temporary factors at work, and as chance would have it, one of them — the eruption of the el Chicon volcano — canceled out most of the 1983 el Niño warming. Here’s my estimate of the effect of all three fluctuation factors (el Niño, volcanic eruptions, and solar variations) on global temperature:

The biggest upward peaks, the times when the world was warmest because of fluctuations (not trend), were the big el Niño peaks of 1998 and 2016.

When we subtract this estimate from the original data, we get an estimate of how temperature has changed in addition to those temporary factors. We can call it the “adjusted” data, and here it is:

The trend is still there, unchanged, but the fluctuations are much smaller, and the steadiness of the uninterrupted warming trend is easy to see.

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If you’re read this far, you probably have more than average interest in global temperature. You might even know already that more than one organization estimates global average temperature. Here’s the yearly average, for the whole globe, according to two of the best-known data sets, one from NASA (we’ve just seen their monthly data), the other from HadCRU (the Hadley Centre/Climate Research Unit in the U.K.):

There’s an obvious trend, and just as obviously it fluctuates around that trend. In fact, as obvious as the trend is, the fluctuations are plenty big enough to be quite noticeable.

We’ve already computed adjusted data for NASA; we can do so for the HadCRU data too. It gives this:

The trend is still the same, but now the fluctuations are a lot smaller. Of course we can never eliminate them, but by at least getting rid of the fluctuations we can explain, we make our view of the trend that much clearer.

And the world’s warming rate? NASA data put it at 0.0178 °C/year, the HadCRU data estimate 0.0177 °C/year. That’s plus or minus 0.0018 °C/year. Basically, they’re telling the same story: 95% chance it’s somewhere between 0.0160 and 0.0196 °C/year.

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