One day, or thirty years
What's the Difference Between Weather and Climate?
Weather is what happened today. Climate is what usually happens — and one cold week says nothing about the other.
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Step 1 of 5
Climate is weather, averaged over a long time.
There is no separate thing being measured. Climate is what you get when thirty years of daily weather is added up and the day-to-day noise cancels out.
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Step 2 of 5
A single day tells you almost nothing.
Any climate has hot days and cold ones. Picking one out proves nothing, in the same way that one tall child says nothing about the height of a school.
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Step 3 of 5
Climate is what you plan around.
Nobody builds a house or plants a crop for tomorrow's forecast. They build for what the place usually does — the frosts, the rains, the worst storm in a lifetime.
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Step 4 of 5
Changing the average changes the extremes.
Shift a whole distribution a little warmer and the everyday barely changes, but the record-breaking hot days become several times more common.
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Step 5 of 5
Which is why both are worth measuring.
The forecast tells you whether to take a coat. The climate record tells you how high to build a sea wall. They answer completely different questions.
Weather forecasts run out of usefulness after a week or two. Climate projections work for decades, because averages are far more predictable than days.
The short version
Weather is one day and climate is decades of them averaged, so a single hot or cold spell says nothing about the trend.
Try it yourself
Write down the temperature each day for a month, then average it. The average is far steadier than any day was.