My adventures in science began relatively late, after an extensive engineering education and 10 years of professional work in aerospace engineering.  (Unless you want to count my very early experiences with science, as the daughter of an inquisitive physicist.  But maybe that is a subject for another blog.)  One of the things that struck me as I started working as a practicing scientist was the importance of vocabulary in science.  I think many people have learned, somewhere in their education, about the crucial difference between “accuracy” and “precision” in measurement – two terms that are pretty much interchangeable to most “regular” people.  (“Accuracy” is how close a measurement is to the actual value of whatever it is you’re trying to measure; “precision” is the repeatability of that measurement.)  Vocabulary of science goes far beyond that, however.

I vividly remember giving one of the first presentations of my new career as a scientist, within the first two years of my career switch.  I was talking about a study I did using computers to calculate how sunlight interacts with clouds of various shapes, and I said something about “water vapor”.  To me, as a pretty expert computer modeler but a rather new scientist, that meant “water in the air” – as in clouds.  But to my audience, that was a complete misstatement.  The term I should have used was “water droplets” – particles of liquid water in the atmosphere.  “Water vapor” of course, as most elementary students learn, is water in the gas phase, which is not what clouds are made of!  Making that mistake in front of a large audience of scientists was a very lasting way to learn the difference, and I’ve never made that mistake again.

Over the years, I’ve learned that the vocabulary of science is really crucial to advancing scientific understanding.  Words have to have meaning to represent science concepts.  As science gets more and more specialized, those meanings must become more and more exact.  This is not restricted entirely to science, of course.  Many specialty areas have their own vocabularies as well:  music, art, education, law.  The list goes on.

One of the most visible places where the vocabulary of science clashes with the vocabulary of regular people is in the use of the term “theory”.  As in “Theory of Evolution”, “Theory of Relativity”, “Theory of Gravitation”, etc.  To a regular person, a theory is just an idea that someone has cooked up – it might even be a pretty crazy idea.  To a scientist, a theory is a proposed explanation that fits a set of observations.  For theories that have been around a long time, like gravity, most of the theory is pretty well understood and pretty solid.  (But don’t ask me to explain how gravity actually does its thing.  I just know that I don’t need to worry about falling off the world.)

Another place where vocabulary has caused some misunderstandings is with climate change.  Originally, the term that was in common usage for this idea was “global warming”.  However, this term is not very descriptive of the observed or predicted situation and many scientists have stopped using it.  The term leads to misconceptions, as has been discussed on this blog previously by Dr. Peggy LeMone in Climate Change Misconceptions and More Climate Change Misconceptions Part 1 and Part 2.  But before we can discuss “climate change” we need to make sure we have the same meaning for the term “climate”.  While the definition is typically something that students learn in elementary school, and can repeat when asked, that doesn’t always mean that they have “got” it – like me with my “water vapor” clouds.

So what is climate, really?  Climate is the weather conditions in a particular place in the world over long time periods.  Those conditions are described by the same things that describe the weather – temperature, pressure, humidity, rainfall, etc. – so they are very closely connected.  But they are not the same!  This is a weird and unintuitive idea, and doesn’t fit well with the day-to-day life and experiences of the average human being.  It’s very common to hear someone make a comment like “Boy it’s hot today!  Climate change must be really kicking in.” or “What Arctic weather!  I guess we don’t have to worry about climate change”.  But this type of comment is mixing apples and oranges.  Let’s think about this for a moment.  Scientists usually define the climate for a given place by using data for 30 years at least; more if they can get it (remember that “over long time periods” in the definition).  So a really cold or warm day (weather) represents at most 1 out of (365 days * 30 years) of information that goes into defining climate.  That’s less than 0.1 percent of the information needed to define the climate – pretty small!

To explore what this means, I went to the US Historical Climatology Network and got the official temperature records for the closest available station to where I live.  Pulling out a 30-year stretch of data beginning in 1974, I get this plot.

Figure 1. Daily average temperature over a 30-year period from an official measurement station at Hopewell, Virginia.

The extreme low temperature in this 30-year period is -23.9 °C (-11 °F).  The extreme high temperature is 40.6 °C (105 °F).  (The high and low are instantaneous temperatures; not daily averages.)  The average temperature for the 30-year period is 16.04 °C (60.88 °F).  Let’s say that today it is very cold – as cold as the coldest day in 30 years.  If we average that in with the 30-year record we get an average, climatological temperature of 60.87 °F. (Sometimes this is also referred to as the “normal” temperature.) One extreme day changes the normal temperature for the region by less than 0.01 °F – an unmeasurable amount!  Let’s say today is instead extremely hot – as hot as the hottest day in 30 years.  The new normal temperature is now 60.885 °F – an even smaller change!  Bottom line:  one day of unusual weather doesn’t change the climate at all.

A little experimentation with this data set shows that it would take at least two and a half weeks of weather at the extreme low or high temperature to change the climatological or normal temperature by 0.1 °F.  And that change is still not measurable except by the most precise of thermometers.  What can we learn from this experiment?  Day-to-day human experience is not a good indicator of climate or climate change.  It takes careful measurements over a long time period (and over large regions as well, but that’s another topic) in order to define and measure climate and climate change.

See if you can identify some vocabulary words in your local newspaper, radio or TV station that are used differently than they are used in your science class.