A Hot Topic: Graphing Temperature Trends

Statistically, it's growing warmer.

March 27, 2019
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Recently, as I was working with a spreadsheet that has all of my weather forecasts for The Old Farmer’s Almanac for the 23 years that I have been making them, it occurred to me that here was a database that contains a great deal of information that might be useful in looking at trends.

To do this, I moved the data around within the spreadsheet to be able to create graphs showing how temperatures have changed over the past 23 years. These graphs show some interesting trends that seem to fit, at least in a general sense, with the idea that it’s growing warmer. 

Above-Normal Temperature “Normals”

Let me explain these graphs. As you may realize, each year we forecast the coming year’s weather for 18 United States regions and seven Canadian ones. The maps of these regions that appear in The Old Farmer’s Almanac print editions and on Almanac.com show several cities within each; it is these cities for which I have compiled data on actual temperatures and how they have departed from normal. 

For example, when I say that the temperature departure for December 2018 was 2.61 degrees F (see Figure 1, below), this means that the average of all of the cities shown on all of these regional maps for the United States and Canada was 2.61 degrees F warmer than their most recent official 30-year normals, which cover the period of 1981–2010. The “normal temperatures” that I use are the official ones updated once each decade by the United States and Canadian government meteorological services, based upon smoothed averages of daily temperatures for the 30-year period covered.

Figure 1: Monthly temperature departures from normal, 1996–2018
Figure 1. Monthly temperature departures from normal, 1996–2018.

Thus, if I say that the 2019 average temperature is 1 degree above normal, this temperature is going to be different from what it would be if I were referring to the 2009 average temperature being 1 degree above normal, because over the ensuing decade the “normal” temperatures would have been recalculated and changed. 

Since temperatures generally have been rising, this means that each decade, when the new “normal” temperatures are computed, they are higher than the previous “normal” temperatures. The effect of this is that a graph that shows how temperatures have departed from normal over the years actually understates the real increase in temperatures, since the normals are rising along with the actual temperatures.

When we examine the graph showing the monthly departure of temperature from normal (Figure 1, above), we see that most—but not all—months in the past 23 years have had temperatures above normal. However, there does not seem to be any clear trend in these temperature departures, or at least not one that I can readily see. The greatest positive departure was 8.67 degrees F back in January 2006, while the greatest negative departure was 4.78 degrees F in December 2000.

12-month_moving_average_departures_from_normal_large_full_width.jpg
Figure 2. 12-month moving average of monthly temperature departures from normal, 1996–2018.

When we look at the 12-month moving average of these departures (Figure 2, above), their pattern becomes more apparent, as there does seem to be a general rising trend in the temperature departures, with nearly all above normal. The only times when this 12-month moving average of temperature departures for the United States and Canada were below normal were in 2001 and 2014.

36-month_moving_average_departures_from_normal_large_full_width.jpg
Figure 3. 36-month moving average of monthly temperature departures from normal, 1996–2018.

Examining the 36-month moving average of temperature departures (Figure 3, above) seems to show a trend emerging. Although there are still peaks and valleys, a general upward trend seems more apparent, with each peak higher than the previous one.

What Causes these Changes?

Meteorologists and climatologists have proposed various explanations for the month-to-month and annual variations, including teleconnections such as El Niño, changes in ocean currents, and changes in solar output. 

As for the clear trend of rising temperatures over the past decades, I have seen only three viable proposed explanations: (1) natural variability (perhaps combined with changes in land use and population), (2) an expected general rise in average temperatures as we are still coming out of the last ice age, and (3) warming temperatures due to human activities that increase the levels of carbon dioxide and other atmospheric greenhouse gases.

Find predicted temperatures for the upcoming year in The 2019 Old Farmer’s Almanac.

Reader Comments

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The trend of warming temperatures

I note when people like to think the planet is warming that there is little to any consideration given to the rising population. The increase of population in cities naturally increase temperature. Because of all the hard surfaces and the continual reduction of greenery. Even in small towns the temperature difference from farm to town where the temperatures are often recorded can be 3 degrees or more in difference a somewhat large amount. As most towns and cities around the world grow it is only natural to see records being broken because of where most records are taken. Secondly much of the temperature data taken for rural and remote locations has been done so for such a short period of time we don't have a reasonable data point to say the planet is warming. Thirdly why do people want to be so concerned about Carbon after all if there is not enough of it the plants will die and so will we. so common stop listening to global warming hoax as if it was a bad thing. In a greenhouse we can add Carbon dioxide to increase plant growth. We really need more of it not less so that the water cycle can operate properly and we can grow more food for our ever growing population. All science 101 stuff the so called scientists seem to conveniently forget. Why?

Thank you Dale. A voice of

Thank you Dale. A voice of reason in the madding crowd.

See, this is what gets me

See, this is what gets me about climate deniers. We, average, ordinary people, can chart the data ourselves and see, without a doubt, that the climate is warming. So, when 97% of the people who have literally spent their whole lives studying this say it's true, and we can see ourselves that it's true, how can you possibly deny it? When literally ALL of the evidence points to it, how can anyone deny it?

some people argue that its

some people argue that its explanation 1 and 2, not 3 and therefore "not our problem"
And they have a somewhat valid point. The data shows warming, it cannot show the cause of the warming. There is some interesting data showing correlation between carbon emissions and temperature rise--but even then it doesn't establish a causation. This same problem came up when we started noticing trends in smoking and lung cancer. The trend was there, but the only way to prove causation would be to carry out an experiment were some randomly chosen people smoke and a control group does not and see if the smokers get more cancer.

Most scientist (all but a very small handful) agree that it is human caused because of the accompanying trends (like carbon emissions).

Science is not religion, and logic is a harsh mistress.

You are confusing two things: the existence of global warming, and the assertion that it is mostly or entirely due to human activity. Even many skeptics agree that there has been some warming, but they also note - from the data - that it depends on the time frame you choose to examine. They may disagree on the amount, and they diverge sharply on the question of causation and on the recommended actions.

I am quite certain that if you choose to dismiss all skeptics as "deniers" - a religious term, not a scientific one - then you will indeed conclude that every "reputable" scientist thinks it's all our fault, and unless we take drastic action - action which always seems to exempt certain people - we are headed for the apocalypse. You might want to source the often-cited "97%" figure, though: it was taken from a survey of the literature, using rather loose criteria, and many of the scientists whose work was referenced have subsequently stated that their papers did not support the conclusions the survey attributed to them. Moreover, another way to interpret the data, from that same survey, is that about ONE percent of scientists drew that conclusion.

I hesitate to introduce calm deductive logic into so passionate a discussion, but allow me to present just a little. In case you aren't familiar with the term "syllogism", it is (from Wikipedia) "a kind of logical argument that applies deductive reasoning to arrive at a conclusion based on two or more propositions that are asserted or assumed to be true."

Here is the global warming syllogism as I often hear it:

(P1) Global warming is real;
(Conclusion) Therefore, we need to make significant - even drastic - changes in our lifestyle, to prevent a catastrophe.

The problem is that the stated Conclusion is not supported by that Proposition - in other words, the argument is irrational. Here is the valid syllogism:

(P1) Global warming is real.
(P2) Global warming is caused primarily by human activity.
(P3) The effects of global warming are predominantly or exclusively negative (or catastrophic).
(P4) Global warming can be substantially mitigated, halted, or reversed by changes in human activity.
(P5) The proposed changes in human activity do not produce other, equally negative consequences.
(P6) The proposed changes in human activity are acceptable to the human population.
(Conclusion) Therefore, it makes sense to call for significant - even drastic - changes in our lifestyle.

My analysis of the whole argument runs to 12 pages, and I am sure you won't want to read it, because I am clearly an ignorant heretic who deserves to be stoned to death - or at least silenced.

Rebuttal

We don't deny that the days are getting warmer. We deny the unproven reasons that are given. One specific action does not necessarily result in a certain reaction. For instance, there is marketing data that shows ice cream sales increase during the summer. The is also criminal data that shows crime increases during the summer. So, can we automatically deduce that if we ban ice cream sales in the summer, then crime will decrease? Of course not! But that is how climate change, a.k.a. global warming, has been deduced. You must prove that ice cream sales directly influences crime. You can't just say it, or assume it, and it be true.

rising temperatures - global warming

Having had a look at your graphs, and they do show a general warming trend, makes me wonder that if similar studies were done throughout the Northern Hemisphere and the Southern Hemisphere, we would see the way the North Pole is tilting so much away from where it was known to be for the last centuries - the Polar shift is becoming more pronounced and because of this, certain areas appear to be and indeed, are becoming warmer. So we shouldn't blame it all on global warming, blame it on Polar Shift. One of these fine days, in the next 1000 or two years time, kerboom, a new ice age.

Polar shift

I think you might be mistaken on what the "polar shift" is. It's a magnetic shift, not a physical one. The Earth's magnetic field plays absolutely no role in climate or weather.

Affect of magnetic pole shift on Climate

In recent years the effect of the movements of molten materials within the core of the planet and more particularly closer to the surface have been being studied. From the early results of these studies it would appear there is a correlation between these movements and climate changes. Therefore I think your categoric debunking That the magnetic pole change doesn't affect climate somewhat unwise. True science fact can only be established by being able to perform the same experiment over and over again and always get the same answer. That fact only apples when the same conditions are used. Most of what is said to be scientific today, appears to me to be science fiction.

rising temperatures - global warming

Having had a look at your graphs, and they do show a general warming trend, makes me wonder that if similar studies were done throughout the Northern Hemisphere and the Southern Hemisphere, we would see the way the North Pole is tilting so much away from where it was known to be for the last centuries - the Polar shift is becoming more pronounced and because of this, certain areas appear to be and indeed, are becoming warmer. So we shouldn't blame it all on global warming, blame it on Polar Shift. One of these fine days, in the next 1000 or two years time, kerboom, a new ice age.

Do you remember the 70s?

I used to own a National Geographic Atlas of the World from the 1975; it commented that there was deep concern about the world moving into a new ice age, because of falling global temperatures since 1945, and reported that scientists of the day were talking about interventions to save the planet - including spreading soot over the arctic to warm it up! People have largely forgotten that prediction, and the "consensus" which created it.

1975

That's because in 1975, the climate was still stable, and might suddenly cool. The last 40 years have seen more warming in the climate than the last twenty THOUSAND combined.

Define "stable".

I'm guessing that the scientists in the mid-1970s did NOT believe the climate to be stable, or they wouldn't have been so worried - and wouldn't have proposed something as drastic as blackening up the Arctic. I would also observe that you get very different impressions when you review the 150-year graph, the 1000-year graph, the 20,000-year graph, and the million-year graph.

I recently read an AP story which referred to a United Nations report that unless humans took immediate action, global climate would be completely beyond our control in a decade. But the report was actually from >1989, and the "deadline" was the year 2000. I also recall a 2005 UN report which predicted "50 million climate refugees by 2010".

Reputable climate scientists were wrong in 1975, wrong in 1989, wrong in 2005. In each case they had "data" which seemed to support those dire predictions - just as they do now. Maybe you don't need to be quite so anxious about the future of your children.

This is what science actually looks like.

Science starts with data, not faith - and not the guilt which comes from affluence. Thank you for a sober presentation of objective data, without wild speculation, baseless extrapolation, or demagoguery.

I wondered for a moment if you could clone yourself, as we need more rational discussion and less screaming - but alas, cloning of an entire personality is ALSO unscientific.

As of my writing this comment, this article has had two votes - a 5 and a 1 - illustrating the difficulty of having a calm discussion of such a polarizing issue. Two guesses as to which vote was mine.

A Hot Topic

I too am disappointed in the author's opinion. I looked back at my temp data at my farm. There is no "warming" trend present over the last 30 years. Cities have grown bigger, with more concrete, yet this is not accounted for. More volcanic activity is also not accounted for. A large eruption spews out more CO2 than the USA over a year. Yet this author does not address these causes. Poor reporting at the best, a political agenda more likely.

Not accounted for?

From the article: "As for the clear trend of rising temperatures over the past decades, I have seen only three viable proposed explanations: (1) natural variability (perhaps combined with changes in land use and population) ..."

He was simply presenting the data, not claiming that anthropogenic global warming was the culprit; but when he referred to "changes in land use and population", I presume that he WAS referring to larger cities with more concrete. Someone with "a political agenda" would have offered only one possible explanation, not three equally plausible ones.

So you're saying your local

So you're saying your local weather data accounts for the whole planet's climate data? Who's the one with a "political agenda" here? One lone data point compared to literally thousands means nothing. Climate science isn't politics. It's SCIENCE. Stop politicizing it and actually listen to those who study it and know what they're talking about, before there is no more habitable world for myself and my children to live in.

Anomalies

Yet if we look at actual temps we do not see an increase. Recall the "pause" in warming when looking at actual temps. None of this temperature departure counting accounts for more reporting stations. More reporting stations statistically generates more departures. Plus this is the same strategy the climate change crowd has been pushing for a few years now, it is not some new revelation taken from the history of the Farmers Almanac as is implied here. The recent article on sun spot activity clearly shows the effects of the sun on temperature and how we are actually going into a cooling time with the solar minimum. If we are getting warmer overall as is the suggestion it is because heat is trapped. Meaning temps get warmer all the time. So record cold winters cannot happen. More importantly there is no correlation with CO levels and temperature. Basically no single cause and effect graph. If CO goes up by "x" temp goes up by "y". But you can match the solar cycle directly to the average temp and it matches. NASA has just such a graph. I'm disappointed that the author pretended they pulled all this data from the archives to arrive at this "startling" conclusion to father the climate change hysteria.

I think you are seeing him as far more hysterical than he is.

"Yet if we look at actual temps we do not see an increase. Recall the "pause" in warming when looking at actual temps."

The so-called "global temperature" hysterically reported in the media is based on a whole lot of assumptions - and in fact a certain amount of fudging of the data, which of course they refer to as "correction factors". The author is simply presenting a more limited data set, with fewer variables; he acknowledges that this is URBAN data, not global data, and specifically mentions this as a possible explanation for the apparent rise.

"Plus this is the same strategy the climate change crowd has been pushing for a few years now, it is not some new revelation taken from the history of the Farmers Almanac as is implied here."

I didn't read it as a "new revelation", but simply as a presentation of a large amount of data the Old Farmer's Almanac had in its database - data which may or may not be included in other presentations. As for him being a part of the "climate change crowd", no one seriously thinks that the climate NEVER changes - the dispute is about the cause; and if he were one of the "true believers", I doubt he would have concluded the article by writing: "As for the clear trend of rising temperatures over the past decades, I have seen only three viable proposed explanations: (1) natural variability (perhaps combined with changes in land use and population), (2) an expected general rise in average temperatures as we are still coming out of the last ice age, and (3) warming temperatures due to human activities that increase the levels of carbon dioxide and other atmospheric greenhouse gases." Surely he would have omitted (1) and (2) and gone straight to (3).

"The recent article on sun spot activity clearly shows the effects of the sun on temperature and how we are actually going into a cooling time with the solar minimum ... you can match the solar cycle directly to the average temp and it matches."

Here's the other part of the author's conclusion: "Meteorologists and climatologists have proposed various explanations for the month-to-month and annual variations, including teleconnections such as El Niño, changes in ocean currents, and changes in solar output." So he DID list solar activity as an important factor. If he were a climate evangelical, would he have admitted that the sun may play a large role, or would he have blamed it all on humans?

Part of the problem with the climate discussion is that people are so irritated by the self-righteous idiots in the debate that they overreact even to thoughtful presentations, seeing demagoguery when none is there. I don't know the author, but I think your reaction is colored by others whom you have heard screaming about this topic, and I'm not sure he really deserved it.

" If we are getting warmer

" If we are getting warmer overall as is the suggestion it is because heat is trapped. Meaning temps get warmer all the time."

You do realize that is the very basis of climate change, right? CO2 traps heat and makes temperatures rise. You literally just defined global warming.
It isn't hysteria. Literally all the data backs it up. We know CO2 correlates with temperature. It has been proven numerous times.
If it were the sun, 2018 would have been a cooler than average year, as we have been in solar minimum since last May. Not only that, it's been the DEEPEST solar minimum on record. However, 2018 was the 4th HOTTEST year on record.
Literally everything you said in your post was an outright lie, except for what I quoted, which is the definition of global warming.

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