Rocket taps his log. "Cool and breezy yesterday, cool and breezy today. I predict cool and breezy forever."
Raven laughs. "Two days is not forever. My grandmother says the summers here used to feel just as hot."
"Used to?" Rocket asks. "How would anyone know what the weather did fifty years ago?"
Nova projects a long ribbon of numbers onto the wall, year after year of temperatures.
"Weather observers have kept records at many places for more than a century," she says.
"What do you notice when you look at all the years together, instead of one day?"
Raven traces the ribbon with her finger. "The ups and downs smooth out. You can see what is normal."
"That," Nova says, "is the difference you are looking for."
The National Weather Service defines climate as the average weather conditions for an area over a long period of time.
To describe a climate, scientists look at averages of temperature, precipitation, humidity, sunshine and wind.
Often those averages cover thirty years. NOAA calls these thirty-year averages Climate Normals.
The current set of Climate Normals is based on weather observed from 1991 to 2020.
In many places in the United States, weather records have been kept for more than 140 years.
| Question | Weather | Climate |
|---|---|---|
| How long? | Minutes, hours, days, weeks | Years and decades |
| What is it? | The state of the atmosphere right now | The average of many years of weather |
| Example | Rain this afternoon | Wet winters most years |
| Who uses it? | You, deciding what to wear today | You, deciding what clothes to own |
NOAA puts it this way: weather tells you what to wear each day. Climate tells you what clothes to keep in your closet.
A cold morning in a warm climate is still weather. One hot day does not change a climate.
| Statement | True or false? |
|---|---|
| One hot day proves the climate has changed. | ? |
| The current Climate Normals use weather from 1991 to 2020. | ? |
| Climate describes the average weather over a long period. | ? |
| Weather and climate mean exactly the same thing. | ? |
A single year can be unusually wet or unusually warm. Averaging many years smooths those bumps out.
That is why Climate Normals use three consecutive decades, and why they are updated as new decades finish.
Climate also changes over longer times. NOAA notes that climate events can unfold over several years or decades.
Even larger climate changes happen over hundreds and thousands of years. You will read that record in week 11.
Clear thinking. Tomorrow is your first Station Lab: you build the tools your log needs.