Weather Is What You Get

Photo: Sippakorn Yamkasikorn

Summitted to Wildsight Golden, By Mike Demuth, P.Eng., P.Geo. Research Geoscientist (Powell River, BC)

As it concerns differentiating weather from climate, there is a not-so-old invocation espoused by climate scientists and casual observers of our environment alike…

Climate is what you expect;

Weather is what you get.

A related concept concerning the difference between climate change and climate variability is something called “stationarity” (for a great interactive tutorial on the differences, check out the NOAA Global Climate Dashboard).

Stationarity, or more specifically statistical stationarity, is based on data having a well-behaved variation about an average value. This data could be, say, a 40-year record of the day of the year that black bear cubs emerge from their maternity dens at some location in northern BC; or data describing the average August nocturnal air temperature measured by a citizen scientist in the Cranberry district of Powell River for the past 40 years.

Under stationarity, that average value and its variability can be used to make predictions of the likelihood of a future event and its magnitude. The 100-year flood level in Grand Forks BC is an example of such a prognostication that you have likely heard about.

Under the influence of climate change, however, simple variability around an average value is replaced by variation around a trend; and predictions based on the notion of stationarity become unreliable and possibly dangerous.

From a landmark article Stationarity is Dead – Whither Water Management? published in the journal Science back in 2008:

Climate change undermines a basic assumption that historically has facilitated management of water supplies, demands, and risks.

Let’s use a simple graph to illustrate stationarity and non-stationarity. The data shown below could represent anything that varies with time – time proceeding from left to right.

The left panel illustrates the basic properties of stationarity — a solid average value surrounded by well-defined variability (SD = Standard Deviation). In a climate and weather context, it defines our experience; our coping range; what we are accustomed to. The right panel illustrates non-stationarity — variation around a trend. This regime is characterized by more frequent and unexpected large/extreme events that may exceed our coping range.

Enduring climate and hydrological conditions beyond our coping range will require adaptation, but it is likely that the ability to adapt will be hampered by something Ian Burton, Emeritus Professor and Climate Change Adaptation specialist at Simon Fraser University, calls the adaptation deficit — where we fail to recognize that the behaviour of our climate system and related services is very quickly heading beyond our coping range and possibly even our adaptation capacity.

Whether it is how we might conceive of and manage forest fire risk in Qathet, BC or predict water flows coming off of the Sliammon Creek/Bunster watershed, not recognizing climate and hydrological non-stationarity and only relying on the past to predict the future is a sure-fired way to exceed our adaptation limits – something those involved in actuarial science and insuring risk are well aware of.

To close, there is lots of talk about the new normal. I believe and fear that this is almost subduing us into thinking that the worst impacts of climate heating are inevitable. I would counter…

The new normal?

It’s anything but normal!


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