Climate variability and climate change: some semantics  [A guest
post from hydrogeologist Anne Jefferson] Last week, the
Southeastern United States received several inches of snow. This
late season snowfall was certainly a novelty, though not an
unprecedented occurrence. But it did stir up conversations among
local residents, especially when the week ended with ~25 degree
Celsius (75 Fahrenheit) sunshine. The weather’s fickleness also
got me thinking about climate variability and climate change and
how easily we can slip up and confuse the two. I even see
scientists (who should know better) conflating variability and
change, so below I offer a short, illustrated tutorial on the
differences.  Hydrometeorological variables – things like
precipitation, streamflow, groundwater levels, temperature, and
humidity – are often expressed as annual or seasonal averages.
The average value of one of those variables over 30 years is
called a climatological normal. Below, I’ve illustrated a
hypothetical climate variable as