1 What is climate change and why is it a big deal?

1.1 What is climate?

A remark usually attributed to Mark Twain sums this up well: ‘Climate is what we expect, weather is what we get.’

Weather varies a lot, from one day to the next. I used to live up in Orkney, where people say that if you don't like the weather, just wait five minutes and it'll change. It's true. You'll often get four seasons in one day.

Climate is the average weather over a longer time (typically 30 years) and a larger scale. We know that in the UK the climate varies (colder and wetter in the north and west; warmer and drier in the south and east) and the Mediterranean climate is a major factor in its appeal as a holiday destination. You may also have heard about equatorial, polar, maritime and continental climates. The bigger the scale and the longer the time period the more confident we can be about the ‘climate’ (because we average out the ‘noise’ or local variation of ‘weather’).

These web-based resources provide additional information

• A rather fine Web-based animation from Oxford University explains this in a few minutes.

• RealClimate hosts a briefing and discussion on the differences between weather and climate.