What should we know about yearly average global temperature trends?
ENSO, of course
Get ready for the media blitz about how 2024 was the hottest year on record and exceeded 1.5°C. In fact, it has already started. For example, the New Scientist writes
2024 is now almost certain to become the first year on record when average temperatures exceed 1.5°C above pre-industrial levels, breaching the threshold set by the Paris Agreement.
“At this point, barring an asteroid impact or a massive volcanic eruption… I think it’s safe to say this will be the first year above 1.5 degrees,” says Zeke Hausfather at US non-profit Berkeley Earth.
in 2024 is set to be the first year that breaches the 1.5°C warming limit (11/6/2024). That’s 2.7°F for those of us in the U.S. Expect to see graphs like that in Figure 1. Note that I’m using NOAA data, and there are slight differences depending on the source. I’m also just averaging the months of each year and not weighting them based on the number of days in the months. Hence the 2.31°F for 2024 (so far) as opposed to the predicted 2.7°F.
You’ll notice in Figure 1 that has increased for the last two year from 1.61°F to 2.31°F. I expect we’ll also see articles about how global average temperature increases are speeding up. ENSO is one of the largest sources of variation in global temperature. Figure 2 is the punchline. I’ll explain how we get there below.
If you are a reader of Briefed by Data, you are familiar with the graph in Figure 3. I update this graph each month in QTRS, with the most recent in QTRS 11/21/2024. The first occurrence of this graph was in my post, The Three Trends of Climate Change (6/8/2023). The key here is that ENSO has a large effect on monthly anomalies, with El Niño months (red) the warmest, La Niña (blue) the coolest, and neutral months in between. Overall, temperature anomalies are increasing at a quadratic rate (those are quadratic functions, x²) and not an exponential rate. A pet peeve of mine is that people call any concave increasing function exponential. That isn’t true.
Anyway, it is worth noting the El Niño months are warming faster than La Niña and netural monhts. In other words, we see a jump in anomolies when El Niño arrives. The proper way to understand Figure 1 is in the context of the ENSO status of the months in the given year.
If I take Figure 3 and replace the trend lines with bars for the average temperature for each year, the pattern starts to emerge as seen in Figure 4. We get a jump in the yearly average when El Niño arrives.
It is hard to see each year in Figure 4 and the corresponding ENSO status of each month. I zoomed in to start at 2000, faded the monthly anomaly bars a bit, and colored the yearly average bars for ENSO status. This gives us Figure 2, reapated here for convenience.
El Niño tends to have a stronger effect the longer it lasts. We see that 2023 had more El Niño monhts than 2024, but they were stronger in 2024. On the other hand, 2022 was all La Niña and a cooler year. It takes a bit of luck to have El Niño impact a large portion of the year. The last time this happened was in 2015 and 2016, when we had record anomalies of 1.65°F and 1.85°F. We didn’t break 1.85°F again until 2022.
What should we expect moving forward? It is likely to be a number of years, maybe 5-10, before we break 2.31°F again. At the same time, we should generally expect that we’ll likely stay above the previous record of 1.85°F, as we will usually see increases for all three ENSO trends.
My issue is that the media will hype this year, as the New Scientist subtiles says
This year’s average global temperature is almost certain to exceed 1.5°C above pre-industrial times – a milestone that should spur urgent action, say climate scientists
Climate change is happening, and it is serious. As I’ve noted in past writings, so far we are doing very little to change this, nor do I expect much to change as we all want abundant cheap energy. Yet, I don’t think hyping one year and not explaining the trends does any good and, in fact, likely causes harm, as it seems like crying wolf given the gaps in record years. What effect will it really have if it takes another 5-10 years before we can say we broke 1.5°C for the second time?
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Please point out if you think something was expressed wrongly or misinterpreted. I'd rather know the truth and understand the world than be correct. I welcome comments and disagreement. We should all be forced to express our opinions and change our minds, but we should also know how to respectfully disagree and move on. Send me article ideas, feedback, or other thoughts at briefedbydata@substack.com.
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I am a tenured mathematics professor at Ithaca College (PhD Math: Stochastic Processes, MS Applied Statistics, MS Math, BS Math, BS Exercise Science), and I consider myself an accidental academic (opinions are my own). I'm a gardener, drummer, rower, runner, inline skater, 46er, and R user. I’ve written the textbooks R for College Mathematics and Statistics and Applied Calculus with R. I welcome any collaborations.