The article begins with the statement that “Global Land temperatures have plummeted by 1°C since the middle of this year — the biggest and steepest fall on record.” There are three problems with using land temperatures over roughly half a year (keep in mind, the article came out on November 30) to infer global trends. The first, as was pointed out by many people, is that 70% of the Earth’s surface is ocean. The second, as a few people pointed out, is that the ocean warms and cools less quickly than land does, so the magnitude of the drop in temperature would be reduced if oceans are included. The third problem, which I’m surprised wasn’t brought up by more people, is that 67% of the Earth’s land is in the Northern Hemisphere. What direction would you expect Northern Hemisphere temperatures to go between the middle of the year and the end of November? So right away you have a number presented in such a way as to make it look far more significant than it really is, and I could understand why people wouldn’t have bothered with the article any further than here.
As far as the “icy silence” from “climate alarmists” was concerned, anybody who understands how global mean temperatures fluctuate would say that a drop in global mean temperatures from the recent peak was long expected as the strong El Niño finally faded and segued into the other side of the natural cycle, called La Niña. But what makes is this article worth examining is that, instead of ignoring the perfectly natural explanation for the temperature variation, Delingpole actually identifies the cause correctly but then mistakenly concludes that it supports the idea that there is no warming trend. He cites another skeptical author named David Rose, who is quoted as follows:
“Big El Ninos always have an immense impact on world weather, triggering higher than normal temperatures over huge swathes of the world. The 2015-16 El Nino was probably the strongest since accurate measurements began, with the water up to 3ºC warmer than usual.
It has now been replaced by a La Nina event – when the water in the same Pacific region turns colder than normal. This also has worldwide impacts, driving temperatures down rather than up.
The satellite measurements over land respond quickly to El Nino and La Nina. Temperatures over the sea are also falling, but not as fast, because the sea retains heat for longer.
This means it is possible that by some yardsticks, 2016 will be declared as hot as 2015 or even slightly hotter – because El Nino did not vanish until the middle of the year. But it is almost certain that next year, large falls will also be measured over the oceans, and by weather station thermometers on the surface of the planet – exactly as happened after the end of the last very strong El Nino in 1998. If so, some experts will be forced to eat their words.”
I’m not actually certain what experts Rose is talking about. Most of what he says outside of the last sentence is at least defensible, although there is room for some argument on the details. (2016 appears to have been more than slightly warmer than 2015, for example.) To illustrate the connection between the El Niño/La Ninã cycle (generally referred to in the scientific community as the El Niño Southern Oscillation, or ENSO) and global mean temperature, I’m going to show a few graphs.
Figure 1
Figure 1 contains the bimonthly mean anomalies, measured relative to the 1951-1980 mean, of global temperatures in the GISS data set. The temperature curve is not a smooth, steady rise, but rather a series of peaks and relative minima oscillating back and forth around a general trend. The most pronounced peak is indeed the most recent one, reaching a bimonthly mean value of 1.33 ºC above the 1951-1980 mean in February/March 2016. The temperature anomaly dropped over half a degree back to 0.80ºC in June/July, which is pretty steep over a short period of time, but it has actually gone up a bit since then.
Figure 2
Figure 2 shows the corresponding bimonthly mean plot of a quantity defined by the National Oceanic and Atmospheric Administration (NOAA) as the Multivariate ENSO Index (MEI). The mathematics of calculating the MEI is complicated, but it revolves around measurements of six different weather-related quantities in the tropical Pacific, and then defining the variance in these quantities relative to median conditions (defined as an MEI of 0). The high positive values correspond to El Niño events, while the strongly negative values correspond to La Niña events. As you can see, many of the temperature spikes in Figure 1 coincide with El Niño events, and many of the relative minima coincide with La Niña events. This is why scientists consider the ENSO cycle to be the dominant source of short-term, natural variations in the global temperature record.
However, while the 2015-2016 El Niño event is among the strongest on record, the MEI data suggest that it was not stronger than the one in 1998. That particular El Niño event produced its own sharp spike in the global temperature record. It has also produced a large amount of misunderstanding of how global mean temperatures work, as skeptics have spent much of the last decade or so declaring the 1998 peak as the point where global warming stopped. It should be clear enough from Figure 1 that there is more at work than the cyclical El Niño variations. The highest bimonthly mean temperature anomaly recorded in 1998, a stronger El Niño than the most recent one according to the MEI data, was 0.75ºC. Not only is that nearly 0.6ºC cooler than the most recent peak in the temperature anomaly from last year, but the 1998 peak was cooler than the planet is right now, even after the large drop.
As for the drop, the 2015-2016 El Niño has certainly ended, but the present state is closer to neutral than to a full-blown La Niña event. This suggests that ENSO-neutral conditions presently result in a temperature anomaly at, or maybe a little bit above, 0.80ºC. Were this state of general neutrality to continue for the rest of the year, 2017 would wind up comfortably being the third warmest on record, but that ultimately depends on whether or not a strong La Niña ultimately happens.
So does that mean, as Delingpole concludes in his article, that “The last three years may eventually come to be seen as the final death rattle of the global warming scare”? No, of course not. The overall trend in the temperature anomaly data continues to be positive. The trend may appear larger or smaller at different times due to natural fluctuations, but it is there just the same. If ENSO were the dominant influence on global mean temperatures without any additional warming trend, then the temperature anomaly from this past year would most likely not be higher at all than the one in 1998, much less 0.6ºC higher.
(Incidentally, I told my climate-related classes in 2015 that it would only be a matter of time before the same people who insist on using the peak of the strong 1998 El Niño as the starting point in their analysis of subsequent temperature trends would start publicly dismissing the much greater peak presently in the temperature record on account of its association with a strong El Niño. And here you go.)
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I heard a scientist state that a warmed up Earth meant a more active Earth and that there would be more extreme events because of it. Doesn't that mean that we would expect deeper drops in temperature as well?
ReplyDeleteLocally, under some circumstances, yes that's possible. People are also definitely looking into how ENSO would change in a warming world, which would include whether or not the natural variations in global mean temperatures would be affected. I don't think any firm or confident conclusions have been drawn in that regard yet, but it's an area of active research. And there are other sources of natural variations as well.
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