The Meaning of 'Climate'
Is it time for a universally accepted and consistent definition of 'climate'?
Readers of The Atlas Report will not be surprised to hear that I often get asked the question:
‘‘Do you believe in climate change?’’
I really dislike this question!
The words in this question are, I believe, ill-defined. I think many of you will agree with me if you take a bit of time to consider it.
Perhaps the obvious place to start is to focus on the word ‘climate’. What do we actually mean by it?
A brief history of the word ‘climate’
As far back as the ancient Greeks, the Earth’s weather was being discussed and recorded. And while he was not the first to discuss what we would now refer to as the ‘climate’, Aristotle was perhaps the first to discuss it in a scientific context. In his book Meteorologica, he uses the word crasis, meaning ‘mixing’ or ‘blending’, when discussing the climate and how it changed according to the Earth’s different latitudes.
The word ‘climate’ was originally used as a purely geographical term to categorize regions of the Earth as defined by their celestial inclination (or latitude). The Greek, Hipparchus, coined the term ‘climate’ which originates from the Greek verb ‘to incline’.
Later the word was used to categorize regions in terms of their general weather conditions. In the period around the time of the birth of Christ, ‘Strabo the Geographer’ first used the term ‘climate’ to mean something like it’s modern meaning, where he linked ‘climatic zones’ to various descriptions of temperature (‘frigid’, ‘temperate’ and ‘torrid’).
The study of the climate - climatology - seems to have been formally defined some time after 1800.
‘‘By climate we mean the average weather as ascertained by many years’ observations.’’ Hebertson, 1907
‘‘Climate lasts all the time and weather only a few days’’ attributed to Mark Twain, circa 1880
From these quotes from around the turn of the 20th century, we can see how ‘climate’ has evolved into a statistical term, being defined as an average of (increasingly large) data sets of meteorological parameters over a given period in a given place.
With the current sophistication of measurement technologies, ‘climate’ can be used to describe conditions of not only the entire planet Earth, but other worlds entirely!
Modern definitions of ‘climate’
Some definitions from modern day institutions include;
‘‘The composite or generally prevailing weather conditions of a region, throughout the year, averaged over a series of years.’’ USA National Weather Service
‘‘The average of weather over at least a 30-year period. Note that the climate taken over different periods of time (30 years, 1000 years) may be different.’’ USA National Weather Service’s Climate Prediction Center
‘‘The slowly varying aspects of the atmosphere–hydrosphere–land surface system. It is typically characterized in terms of suitable averages of the climate system over periods of a month or more, taking into consideration the variability in time of these averaged quantities.’’ American Meteorological Society
‘‘Climate in a narrow sense is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years.’’ IPCC
‘‘Climate… is the average of these [weather] conditions over longer time periods ranging from years to decades.’’ UK Met Office
Dictionary definitions sometimes use the word ‘prevalence’ - having the most influence - to describe the weather conditions that would constitute the ‘climate’ of a given area, for example:
‘‘the weather conditions prevailing in an area in general or over a long period’’ Oxford Dictionary
‘‘the composite or generally prevailing weather conditions of a region’’ dictionary.com
Would a constant climate be ‘normal’?
We can see that ‘climate’ has become a statistical averaging of real world conditions. As is so often the case with statistics, one must be very careful not to be mislead by mathematical abstractions.
Mother Nature changes the weather, statisticians change the climate.
The use of a long-term statistical average can give the impression that ‘climate’ has been, and therefore should always be, stable.
When presenting current temperature trends the term ‘anomaly’ is often used to illustrate changes against a longer term average. But why use the term ‘anomaly’?
The word ‘anomaly’ reinforces the idea that ‘climate’ should be constant, and anything that deviates from the (arbitrarily derived) average is therefore an ‘abnormality’ or ‘irregularity’.
There is, however, much evidence that the ‘climate’ has been in a constant state of change.
In other words, a deviation from any arbitrarily assigned mean value is in fact perfectly ‘normal’ for any system, particularly one as complex and ever-changing as the climate.
Moving the goalposts
Unless you have a perfectly stable system, one would expect changes relative to the average. Simply changing the averaging period against which you are comparing a particular condition will not only change the extent of that change, but potentially even its’ direction. Again, beware of statistics!
To illustrate this point, the chart below presents satellite-derived, global surface temperature trends over various time periods, up to June 2021.
‘‘The time period is, quite evidently, extremely critical; global surface temperatures have, for example, cooled over the last 5 years.’’
Is a more rigorous definition of ‘climate’ necessary?
Do we need a definition that doesn’t (either deliberately or unknowingly) mislead us into believing that a static climate is ‘normal’? One that doesn’t leave us vulnerable to the dark arts of the statisticians or their political or economic influencers?
After all, there is now so much staked on this concept of the ‘climate’ - which is at present a statistical abstraction - and the manner in which it is apparently changing.
But again, changing relative to what? There is currently no universal definition that answers that central question.
I recently read an interesting paper from the National Technical University of Athens which made the bold case for a new, stochastic definition of ‘climate’. In other words, a definition that mathematically accounts for the element of randomness in the climate through the use of probabilities.
Summary
The difference between weather and climate is not universally and consistently defined.
The term ‘climate’ can be broadly summarized as ‘the average weather’.
The meaning has changed over time from an astronomical one, to a geographic one, to the modern day meaning which incorporates meteorology and statistics.
I believe that the modern definition gives the misleading impression that the ‘normal’ state of the ‘climate’ is unchanging and constant, and therefore any such change is considered ‘abnormal’.
Is it time for a more rigorous and universal definition of ‘climate’?
Why I still hate that question?!
Unless you believe in a static ‘climate’, weather conditions will deviate from their statistical averages. But which statistical average do you mean? And how do you account for the inherent randomness of the weather when considering those changes?
The weather will always change, and the ‘climate’ along with it.
So, do I believe that the climate is changing? Yes, of course.
While I’m not sure that is exactly the answer people want when they ask the question of whether I believe in climate change, it will have to do for now!
-Tristan