What is the difference between weather and climate?

Weather is the short-term, day-to-day state of the atmosphere, the temperature, rain, wind, and conditions right now or over the coming days, the stuff a forecast predicts. Climate is the long-term pattern, the average of weather over many years, typically 30 or more, in a place or across the planet. A useful analogy: weather is your mood on a given day, which swings around unpredictably, while climate is your personality, the stable underlying pattern you can count on. Phoenix has a hot, dry climate even on the rare day it rains; Seattle has a wet climate even during a sunny stretch. Weather is measured in hours and days; climate is measured in decades and centuries.

This distinction matters enormously because confusing the two produces a lot of bad reasoning, especially around climate change. A single cold day, or even a brutally cold winter, does not disprove global warming, because warming refers to the long-term rise in average global climate, not the guarantee that every day everywhere will be warm; weather still fluctuates wildly around the slowly shifting climate average. Likewise, one hot day is weather, not proof of climate change by itself. The signal of a changing climate shows up in long-term trends, decades of rising global average temperatures, shifting patterns, more frequent extremes, not in any individual day's weather. That is why the it snowed, so much for global warming line is a category error: it uses weather to argue about climate. The clean way to hold it: weather is what you get, climate is what you expect, and it takes many years of data, not one day's experience, to say anything about climate.