Defining "weather" and "climate"

Greetings Readers,

In this post, we will define and distinguish between the scientific definitions of "weather" and "climate". In practice, these terms are often used interchangeably which can lead to confusion depending upon the audience.

For a scientific definition of weather and climate, we can source the National Oceanic and Atmospheric Administration (NOAA), which is the U.S. government agency that studies atmospheric, ocean, and other earth sciences. NOAA says:

"Weather is what you experience when you step outside on any given day. In other words, it is the state of the atmosphere at a particular location over the short-term. Climate is the average of the weather patterns in a location over a longer period of time, usually 30 years or more."

On this blog, to keep things simple, we ignore the time element and use the term "climate" to describe atmospheric phenomena and events generally. Although the climate scientist in me cringes when doing this, my choice to use the word climate as a catch-all term is influenced by the decision of the financial world (i.e. investors, regulators, service providers) to use the word "climate" when discussing the natural risks posed to the global economy. (In future posts, when discussing the evolution of risk over time, we will take care to describe and distinguish between weather and climate.)

When predicting the future state of the atmosphere--and using those predictions to make financial decisions--one should be aware of the differences between weather and climate. It is important for users of forecast information to understand the forecast skill and uncertainty embedded within short-term weather forecasts and long-term climate forecasts.

To drive home this point we use an analogy. Imagine we asked you to predict where Prime is physically located. A 'climate forecast' would predict my average location on any given day. A 'weather forecast' of my location would predict the path of my precise location throughout the day. 

Climate forecast analogy

The 'climate forecast' for my location is skillful to the extent that it predicts my general location during each day. On average, Prime is:

[at home] from 6pm-7am

[traveling to work] from 7-8am

[at work] from 8am-5pm

[traveling home] from 5-6pm. 

Weather forecast analogy

The 'weather forecast' for my location is skillful in its ability to predict my path taken on any individual day. On a particular day, Prime is:

[eating dinner, reading, sleeping, getting dressed, eating breakfast] from 6pm-7am

[walking from home to train, riding train, walking from train to office] from 7-8am

[working at desk, eating in cafeteria, meeting in conference room] from 8am-5pm

[walking from office to train, riding train, walking from train to store, walking from store to home] from 5-6pm

Another analogy that I like is shown in a nice animation that was produced by the National Center for Atmospheric Research. It describes how the likelihood of a baseball player hitting a homerun in baseball on a given day and over time (akin to occurrence of a weather event) can be influenced by a player's decision to take performance-enhancing drugs (altering the system within which events occur, akin to a changing climate system).

I hope this post helps address the nuance that exists between the words "weather" and "climate", even though you'll typically hear me and the world often use the word climate as a catch-all to address natural phenomena that can cause financial risk and opportunity.

Best,

Prime