Weather isn’t climate

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Is it real?

Mixing up weather and climate is a common problem. The main way we experience the climate where we live is through our weather. But weather is not the same thing as climate. And in particular the basis for trusting a weather forecast is very different to the reason we might trust a climate forecast.

Climate is made out of weather. It’s the collection of different types of weather which are possible in a location combined with the probability each one has of happening.

There are lots of different analogies possible here. Try these out for size:

A picture on screen is made out of lots of tiny dots. Each of the dots is part of the picture but looking at one (or a few) won’t show you the whole picture or even its colour.

A town or city has lots of different streets and buildings in it. Visiting a single building may tell you something about the city, but you won’t get an overall picture of what the whole place is like.

Think about your life. Now think about one day in your life. If someone looked at the single day, they wouldn’t be able to tell if it was a normal day or not, or what the other days were like. If you were ill that day, would it be fair to say you are always ill? If you were unhappy, could they decide you are generally an unhappy person? You need to know about a lot of days before you can start drawing conclusions.

Climate is like this. You can’t take one day’s (or one season’s, or one year’s) weather and say that this shows us the climate. But as we build up records of weather over years and decades, patterns emerge. So we know that tornadoes tend to happen in certain parts of the USA in certain seasons, or how rainfall varies through the year or how tropical monsoons vary.

We can’t say that a particular weather event is caused by climate change; but if a general pattern changes, if the probability of different types of weather change – like the rainy season shifting earlier or later, or the intensity of the rain changing – then climate has changed. A major effort in climate science is to identify such changes amidst the huge variability in weather events. Variability which can happen from day to day, year to year, decade to decade.

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