(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Scientists can’t even predict the weather next week, so why should we believe what some climate model tells us about 100 years from now?

Answer: Climate and weather are very different things, and the level of predictability is comparably different.

Climate is defined as weather averaged over a period of time — generally around 30 years. This averaging smooths out the random and unpredictable behaviour of weather. Think of it as the difference between trying to predict the height of the fifth wave from now versus predicting the height of tomorrow’s high tide. The former is a challenge — to which your salty, wet sneakers will bear witness — but the latter is routine and reliable.

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This is not to say it’s easy to predict climate changes. But seizing on meteorologists’ failures to cast doubt on a climate model’s 100-year projection is an argument of ignorance.