"Climate is average weather" is the line everyone uses, but averages over what, and why thirty years specifically? It sounds like a convention rather than a threshold with meaning.
Is there a real statistical reason for the separation?
Accepted Answer
Climate is the distribution. Weather is a sample drawn from it.
That is the useful framing, because it makes clear that climate includes variance and extremes, not only the mean. A warming climate is a distribution shifting and changing shape, which is why record highs outpace record lows even though individual cold days still happen.
The thirty years is a convention, from the World Meteorological Organization, and chosen because it is long enough to average out interannual variability such as El Niño while short enough to stay relevant. It is not a physical constant, and other periods are used when the question calls for them.
The common mistake that follows from "climate is average weather" is worth naming, since it is the source of the cold snap argument.
A single cold winter is a sample from the distribution. It cannot refute a claim about the distribution, any more than one tall person refutes a claim about average height.
The reverse error is just as common and less often called out. A single heatwave does not confirm the claim either. Attribution needs the statistics of many events, which is what attribution science actually does.
The everyday version I use: climate is what you pack for, weather is what you get. It survives contact with the statistics better than most slogans.
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