What is the difference between weather and climate? It is quite complicated and quite frankly arbitrary and I personally do not like the NOAA definition of climate but this blog post sheds a little light on the subject.
It was posted in late January and it contains three short YouTubes you can watch that show how averaging turns weather into climate. It is not as precise as I would like but it at least starts the conversation. The post was written by Michelle L’Heureux
As many of the ENSO Bloggers do from time to time they intertwine the science with personal experience which may help in understanding the concept.
The official NOAA definition of Climate is the average over the last three completed decades so currently that is 1991 -2020. I do not like that definition because it does not reflect the influence of long cycles such as the AMO and PDO but I can not think of a better definition.
You can read the Blog Post with the comments HERE But I have reproduced most of the post in this article with some of my comments so click “Read More” to read my article.
Note: On Friday we published an article on the NOAA update of the ENSO Alert and that can be accessed HERE.
Now we hear from Michelle L’Heuraux
With the arrival of the new year and an ongoing strong El Niño, many folks are already asking us, why isn’t the current El Niño bringing the expected wetter/drier/warmer/cooler conditions over my house yet?!
First, we’ve already seen impacts consistent with El Niño across much of the globe and those impacts have been occurring for some time now. A quick look around the world indicates some very El Niño-like impacts over the past half year (footnote #1).
Second, we’re two-thirds through January as of this writing, which means we’re barely past the midway point in the December-February season. We’ve basically just entered the January-March season when the U.S. El Niño impacts are most widespread (El Niño’s sea surface temperature typically peaks a couple of months earlier, but there’s a lag). It’s just too soon to say much because, as we’ve discussed, ENSO is a seasonal climate phenomenon and primarily impacts seasonal climate averages. That’s right—ideally, we wait *three whole months* (footnote #2) to look back and examine a given winter’s consistency with the historical El Niño impacts (footnote #3).
With that said, we totally understand the curiosity about whether El Niño impacts are being felt or if factors other than El Niño will wind up dominating this winter. I will admit to staring at the near-term weather forecasts a bit too often over the past couple weeks (hooray for mid-Atlantic snow!).
Happy children enjoying a weather event that provided at least 4 inches of new snowfall (two storms in one week in the DC area!). They’ve said their prayers to the deities of El Nino and the polar vortex to produce similar snowy events this winter. Photo credit: M. L’Heureux.
But I have to remind myself that weather and climate are two very different things. It’s not easy! After all, our lived experience from day to day, what we see and feel, is the weather. It’s a bit harder to “feel” the climate, which is the average of weather over different spans of time (footnote #4). I don’t generally go on a stroll in the morning and think to myself, “I better bring a raincoat because today’s 1-month average sure feels wet.”
But those averages are the climate! And so, to understand the climate, we have to examine longer time periods. If this is still a bit confusing, I’m going to try out an analogy. And if it is lousy, you can immediately close your browser window and we will forget this ever happened.
Hit the gym
In honor of the New Year, many of us make resolutions to improve ourselves over the coming year. A popular one is to become fitter, by eating more balanced meals and exercising. I’m in this category and in early January, I bought one of those 1-month reduced-price gym memberships because this is THE YEAR I will become fit enough to do a pull-up (footnote #5).
So, what does my New Year’s fitness resolution have to do with weather vs. climate? Well, let’s take a look at the animation below. What you are seeing here is an animation of daily-average weather (precipitation and pressure changes) from the 1st of December 2023 through the 20th of January 2024 (footnote #6).
To watch this animation Click HERE and when you get the full display of the Youtube. Then click the start arrow.
Daily pressure patterns (highs in brown, lows in purple) and precipitation (grayscale) in Northern Hemisphere winter to date (2023-24). There’s a lot of motion in this movie; lots of variability from day to day. That’s the weather. Video by NOAA Climate.gov, adapted from original by Michelle L’ Heureux.
The upshot of this animation is that the weather is chaotic and noisy! Look at all that movement, particularly outside of the tropics and in the middle-to-high latitudes! It’s dizzying. The division between the purple and oranges is where regions of higher pressure (orange shading) meet lower pressure (purple shading). This boundary is often the location of weather fronts which bring rapid changes in the weather. The most dramatic example of this tends to occur ahead of low-pressure systems (the purple shading) that bring rain or snow. Pretty cool, isn’t it?
The movement in this map is a lot like me actively doing some crunches or repetitions on a weight machine at the gym on a certain day. I’m moving, it’s happening! My physical activity over 1 day is super high! If I go to the gym enough, I’m going to be able to do that pull-up! But, oh wait…
Portion control
It’s now two weeks into my resolution and I’ve skipped a few workouts and–confession–there were a few nights in a row when I consumed that extra-large cheesy pizza. Now maybe I’m a little behind on my goals and feeling a bit more sluggish. It’s not a total loss—after all I did do some of my daily workouts. But my physical activity is lower over the 2-week average than for the days that I went to the gym. By evaluating our physical activity over longer spans of time (our overall fitness), we are now shifting from weather to climate timescales.
To watch this animation Click HERE and when you get the full display of the Youtube click the start arrow.
2-week rolling averages of pressure patterns (highs in brown, lows in purple) and precipitation (grayscale) in Northern Hemisphere winter to date (2023-24). Compared to the daily animation, changes have slowed down, like we’re playing back the daily animation at half speed. That’s still weather, but we’re shifting toward climate. Video by NOAA Climate.gov, adapted from original by Michelle L’ Heureux.
The 2-week average animation above is made up of the exact same data as in my 1-day animation except now I’m averaging together 14 days in a row and then sliding this 14-day average forward one day at a time. So, December 1- 14th is the first snapshot, then December 2nd-15th is the second snapshot, etc. What do you notice here?
You may notice that the animation changes a lot more slowly. The chaos inherent in the daily animation is much reduced. There is still movement, but not as much. Some interesting aspects of this animation is the precipitation we see in the global tropics. If you watch it loop a few times you will notice in that you see a distinctive dark band of shading across the tropical Pacific Ocean—these are clusters of storms that have been generally more active (see Emily’s recent post) because of the ongoing El Niño!
As we slide forward in time, we can see the storminess in the tropical Pacific Ocean becomes reduced and, gradually, the storm cluster over the tropical Indian Ocean gets stronger and then starts shifting toward Indonesia. What is this? This fluctuation is, in part, driven by the Madden-Julian Oscillation (MJO), which is a dominant driver of the tropical climate (and an important factor in U.S. conditions) on “sub-seasonal” timescales. Fancy word, but all “sub-seasonal” means is that we are looking at climate averages shorter than a season, such as two weeks or a month. In the first half of January, the MJO was moving into locations (we describe them as phases) that enhance rainfall in the Indian Ocean/Indonesia and suppress it over the tropical Pacific—a geographic arrangement that opposes the effects of El Niño.
There are a lot of interesting features in this animation, but since we are a United States-based blog, let’s shift our attention the U.S. From mid-December through the beginning of January, we saw lower pressures (purple shading) dominate the eastern North Pacific Ocean (off the West Coast). We saw a similar area of lower pressure near the southeastern United States. Over Canada and the northern tier of the U.S., there was a region of higher pressures. This observed pattern overlapped strongly with the expected El Niño pattern. However, since early January, we’ve seen that atmospheric pattern break down, likely partially due to the MJO.
Slow and steady wins the race
Let’s increase the averaging length further and move onto a monthly (4-week) average. Now it’s harder to see the sort of drastic changes that are obvious in daily or 2-week averages.
To watch this animation Click HERE and when you get the full display of the Youtube click the start arrow.
Rolling 4-week average of daily pressure patterns (highs in brown, lows in purple) and precipitation (grayscale) in Northern Hemisphere winter to date (2023-24). Compared the daily and even 2-week animations, changes are much more subtle, like we’ve switched to 1/4 speed slow motion. Not weather, but not yet a full season (which is the climate period El Niño forecasters pay attention to), a month is typically described as “sub-seasonal” climate. Video by NOAA Climate.gov, adapted from original by Michelle L’ Heureux.
The band of tropical precipitation is steadier and is more consistent with the typical conditions this time of year (though El Niño enhances rainfall over the equatorial Pacific Ocean). Over North America, we see a persistent pattern of higher pressure over Canada and the northern tier of the U.S., with lower pressure over the eastern Pacific and southern U.S. We can also see higher amounts of precipitation in the southeastern U.S. These are all features consistent with El Niño that were more difficult to spot in the daily or two-week averages!
So, here at the monthly level, we have hints of an El Niño influence, but we need to still remember El Niño describes only a small part of sub-seasonal variability. It is very common to see variations in the 4-week average within a season and these may have nothing to do with El Niño.
So, can you do that pull-up now?
No, not yet. While the chances (probabilities) are in favor of me getting closer to my fitness goal the more I go to the gym and eat right, it doesn’t mean I’ll be able be fit enough to do a pull-up by the end of the year. In the same fashion, weather patterns can average over time to be consistent with the influence of El Niño, but rarely do they perfectly match El Niño expectations (see Nat’s awesome blog post that illustrates how much “matching” we can expect between U.S. precipitation and ENSO). Why is that?
Well, go back to that 1-day animation map and stare at it some more. Weather is chaotic! If I told you that on a certain day, one month from now, a cold front will move through the central Plains and it’ll be rainy and 35° Fahrenheit, you should laugh me out of the room. El Niño is never going to tell you what the WEATHER will be on a certain day. What El Niño can tell us is that, for seasonal averages, chances favor more storm systems and precipitation over the southern tier of states in the winter/early spring (along with these other impacts).
But just like my 1-day workout in the gym isn’t going to tell me whether I will be fit enough to do a pull-up by the end of the year, looking at short spans of time isn’t necessarily going to reveal whether El Niño left its mark. It’ll be the average of my eating habits and workouts (weather) that tells the story of my overall fitness (climate). And, even then, there might be surprises in store: my fitness could deteriorate for some other reason like illness or injury—things that are unpredictable. On that uplifting note, Happy New Year! I’m going to hit the gym.
Editor’s Note: You can see that in this example the longer averaging time from the first YouTube to the third revealed a more stable situation. But there is a corresponding problem of what to do when there is a secular trend such as Global Warming. We will talk about that in a future article. The below footnotes show what we might have learned from this exercise about El Nino or would if we used a longer averaging time and considered multiple El Nino events.
Footnotes:
(1) Some impacts that are likely partially attributable to (consistent with) El Niño relationships include:
decreased precipitation and drought across northern areas of South America and parts of Central America since at least June 2023.
flooding rains and increased precipitation near the Horn of Africa in October-November 2023.
drier conditions around Indonesia and the Philippines since August 2023.
drier conditions over Australia during August-October 2023.
wetter conditions across southern India and Sri Lanka during October-December 2023.
increased precipitation near Uruguay/southern Brazil since September 2023.
Also read footnote #3 and realize many of these impacts also occur within a warming world so cannot be solely attributed to El Niño (see this interesting recent analysis on the Amazon).
(2) This can be confusing, but when we say “seasons” we mean any 3-month period. Not the conventional “winter,” “summer,” etc. A season here can be December-February, January-March, February-April, March-May… you get the picture.
(3) To be clear, consistency with historical El Niño impacts is a pretty low bar for determining whether anomalies were driven by El Niño. To get more serious about attribution, one could run models driven with observed tropical Pacific Sea surface temperature (like what was shown in this post) to see what degree the climate response to the sea surface temperatures matched both the expected El Niño signal and what actually occurred.
(4) I’m simplifying here a bit by saying it’s just “averages.” Climate can be defined by other metrics that make up a probability distribution. For example, we could look at changes in the variability (variance/standard deviation) over different time spans.
(5) Ha ha. This is a total lie. I will never be able to do a pull-up as long as I live. But I’m going to try to be healthier and that’s good enough for me.
(6) As a friend points out, to make this a better analogy, we’d start this loop on January 1st. He also says the animation loop should end when everyone gives up their New Year’s resolutions.
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I hope you found this article interesting and useful.
Mr. Silber is a mathematician and an economist with many years of experience in a variety of technologies. He started his career at Bell Telephone Laboratories and has worked in and provided consulting to many participants in the computer and communications industries. He has also been very involved with Natural Resources having been a V.P. of Planning and Financial Analysis for Kennecott Minerals. Mr. Silber has also taught a graduate course in Information Economics at Polytechnic University which is now part of New York University. Mr. Silber has served as an elected Supervisor and Secretary Treasurer of the Santa Fe - Pojoaque Soil and Water Conservation District. In addition to his consulting practice, Mr. Silber is working on a book that will address the economic issues related to Global Warming.
