When does summer start anyway?

There is much debate over exactly when summer starts and ends. This is because in North America, summer runs from the solstice to the equinox while in other parts of the world, it runs from the cross-quarter day before the solstice to the cross-quarter day after it. To further muddy the waters, yet other places split the difference between the two. I am going to examine why the debate is stupid and the calendar definitions even stupider.

First, what is summer anyway? Generally, it is the warmest time of year with, on average, the longest days. In areas with cold winters, it is usually the bulk of the growing season. In other areas, summer might actually be the time with the least growth, sometimes being the dry season. In short, the specific definition of what summer is depends on where one is located on the Earth. It has historically been a fairly informal distinction.

Things might be clearer in the context of the other seasons. Winter is obviously the coldest time of year, usually associated with the shortest days and, in many parts of the world, snow or storms. In colder climates, little or no plant growth occurs either due to lack of light or the fact that the ground is too cold. Summer is the opposite time of year. Spring is merely the transition from winter to summer and autumn is merely the transition from summer to winter.

Depending where one is located, the relative lengths of the various seasons vary. Further from the equator tends to experience longer winters while closer to the equator experiences longer summers. At the equator, the weather tends to stay fairly consistent year round and one can consider the equator to be essentially seasonless. (That is not truly the case, but the important distinctions have little to do with summer or winter.)

Again, depending on latitude, spring and autumn may be longer or shorter. In more extreme latitudes, the sun moves more significantly between equinox and solstice than at lower latitudes. This means that the increase in daylight intensity and length is more marked. This tends to lead to more marked season shifts.

So what does this all mean? Well, where I am in southern Alberta, winter can arrive as early as October and last as late as May. Yes, that is nearly nine months. That is the extreme case, however. Usually, it is closer to late November through early April. Spring starts as soon as the weather breaks, the temperature increases above freezing most nights, and it usually comes with rain or wet snow (snow earlier with rain later). Summer arrives usually around mid to late May and lasts until some time in September at which point autumn begins. Autumn is usually fairly dry and comes with trees going dormant. Depending on the tree, it may start to show its “fall colours” as early as early August but most native species do not do so until September, often not until the first “killing frost”. In other words, spring is often quite short, summer fairly long, autumn variable, and winter quite long.

Now, what I have described is approximately correct for my area. Move several hundred kilometres north and the timing changes. Move several hundred kilometres east and things change. Move up in altitude and things change. Place an ocean with a warm current beside land and things change (such as the gulf stream and Europe). In some parts of the world, the four seasons are roughly equal lengths. In many others, there are no real seasons. In yet others, one or two seasons dominate.

Our modern world, however, has decided that seasons must each be one quarter of the year for everyone. These calendar seasons might make sense for small parts of the world where the seasons approximately agree. However, trying to apply the same definition across a large geographic area, say Canada or Europe or what have you is insane. In doing so, one must pick a dividing line and stick with it whether it makes sense across the whole area or not.

To further complicate matters, there are also seasons defined in circumstances other than common usage. Meteorological seasons are fairly reasonable in many areas, taking into account the lag between change in day length and the actual change in temperature. Astronomers like to define things in precise terms using the solstices and equinoxes as the centre points for the seasons. And then there are bureaucratic situations which often assign even quarters to the seasons with the dividing line often being somewhat arbitrary.

The practical upshot of all this is that the debate about “the one true start of summer” and related nonsense is just that. Nonsense. First, the specific context in which the question is asked will change the answer. Second, most people couldn’t care less what some scientist somewhere thinks should be the start of summer and they care only marginally more about some bureaucrat. What most people care about is what the weather is doing outside their door at any given time. It is that weather that defines what the season is. And the changing weather is variable, as we all know. That is, the changes don’t always happen at the same time every year. So picking a fixed date on a calendar for the start of any season is nuts.

So the next time someone starts the debate about when summer start or ends (or any other season, for that matter), ask them about the context of their assertion. Ask them to define the characteristics of the seasons and then ask them when those characteristics are often met in the local area. Either or both of you might be surprised at what you discover.

 

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