Climate vs Weather

People often use the words "climate" and "weather" as if they meant the same thing, but they are actually different. Weather is what is happening outside right now (or in the next few days): the temperature, the wind, the rain or sunshine. Climate is the long-term average of weather in a particular place over many decades. The often-used phrase is: "climate is what you expect; weather is what you get". The difference matters a lot when discussing modern issues like climate change, because warming the climate does not mean every single day becomes warmer; it changes the long-term averages.

  • Weather timescaleHours to daysWhat is happening now
  • Climate timescale30+ yearsLong-term averages
  • Britain's climateTemperate maritimeMild, wet, cloudy
  • Tropical climateHot and wet all yearNear the equator
  • Polar climateCold and dryHigh latitudes
  • Climate changeReal and observableApproximately +1.2 degrees C since 1850

The difference in detail

Weather is the day-to-day state of the atmosphere. A given town might have:

  • Yesterday: sunny and warm.
  • Today: rainy and cool.
  • Tomorrow: windy with showers.
  • Day after: clearing up.

That is weather: short-term changes, varying from day to day or even hour to hour.

Climate, in contrast, is the long-term average of all that weather. The climate of London, for example, can be described as:

  • Mild winters (average around 5 degrees C).
  • Warm summers (average around 18 degrees C).
  • Rainfall fairly evenly spread through the year (around 600 mm total).
  • Frequent cloud cover.
  • Few extreme temperatures in either direction.

That is London's climate. Today's weather might be very different from average, but over 30 years the averages settle out into a clear pattern.

The world's main climate zones

Geographers and climate scientists usually divide the world into about 5 main climate zones, based on the famous Koppen climate classification.

  • Tropical (A): hot all year, lots of rain. Near the equator. Includes Amazon, Congo and Indonesian rainforests.
  • Dry (B): low rainfall. Includes deserts and semi-arid lands.
  • Temperate (C): mild temperatures, four seasons. Includes most of Europe, eastern USA, parts of China.
  • Continental (D): big differences between hot summers and cold winters. Includes central Russia, central USA, central Canada.
  • Polar (E): cold all year. Includes the Arctic and Antarctic.

What makes climate

Several factors shape the climate of any place.

  • Latitude: how far from the equator. Places near the equator get direct sunlight all year and are hot. Places near the poles get slanted sunlight and are cold.
  • Altitude: temperature drops by about 6.5 degrees C for every kilometre you go up. Mountains have cooler climates than nearby lowlands.
  • Distance from the sea: oceans moderate temperatures. Coastal places have milder winters and cooler summers than inland places at the same latitude.
  • Ocean currents: warm currents (like the Gulf Stream) carry heat to higher latitudes. Cold currents make nearby coasts cooler.
  • Wind patterns: global wind belts (trade winds, westerlies) bring different weather to different parts of the world.
  • Mountains: can block clouds and create rain shadows, making one side of a mountain wet and the other side dry.
Fact The reason Britain has a mild climate despite being so far north is the Gulf Stream: a warm Atlantic Ocean current that flows from the Gulf of Mexico across the Atlantic to north-west Europe. The Gulf Stream keeps the UK and Ireland approximately 5 to 10 degrees C warmer in winter than they would be without it. Places at the same latitude in Canada (like Hudson Bay) are frozen solid in winter, but London is mild and rainy.

Climate change

One of the biggest scientific findings of our time is that the world's climate is changing. The global average temperature has risen by approximately 1.2 degrees C above pre-industrial levels (since around 1850). The cause is the extra greenhouse gases (especially carbon dioxide) that humans have been adding to the atmosphere by burning coal, oil and gas, plus cutting down forests.

Importantly, climate change does not mean every day will be warmer. It means averages shift. Some places get hotter; others may actually get colder if ocean currents change. Heatwaves become more frequent and intense. Droughts and floods both become more common. Sea levels rise as polar ice melts. These changes are already measurable and are expected to accelerate over the coming decades unless greenhouse gas emissions are dramatically reduced.

Did you know? One single hot summer day in Britain is "weather". Britain having its hottest year on record in 2022, then matching it in subsequent years, with average temperatures clearly above the 30-year baseline, is "climate" (specifically, climate change). The difference between the two is one of the most common sources of confusion in modern discussions about the environment.
Deeper dive: how scientists know the climate is changing

The evidence that Earth's climate is warming comes from many completely independent sources. Together they paint a picture so consistent that essentially every climate scientist in the world accepts it.

The lines of evidence include:

  • Thermometer records: tens of thousands of weather stations around the world have been measuring temperatures for over 150 years. The trend is clearly upwards.
  • Satellite measurements: since the 1970s, satellites have measured surface and atmospheric temperatures across the entire planet. They confirm the warming trend.
  • Melting glaciers and ice sheets: glaciers around the world are retreating. Arctic sea ice has shrunk by approximately 13% per decade since 1979. Antarctic ice loss has accelerated dramatically since 2000.
  • Rising sea levels: global average sea level has risen by approximately 25 cm since 1880, partly from melting ice and partly from warm water expanding.
  • Earlier spring events: birds nesting earlier, flowers blooming earlier, leaves coming out earlier than in the past.
  • Coral bleaching: warmer oceans are stressing reefs around the world.
  • Ice cores: long cylinders of ice drilled from Antarctica and Greenland show CO2 levels and temperatures over the last 800,000 years. The current rise in both is faster than anything in that long record.
  • Ocean warming: the oceans have absorbed about 90% of the extra heat from greenhouse gases. They are now warmer than at any time in measurable history.

Each of these lines of evidence comes from independent science teams using different methods. The fact that they all agree is one of the strongest reasons climate scientists are so confident in their conclusions. As the famous slogan puts it: "The climate is changing. The science is settled. What remains is what we do about it."

For more on how the atmosphere works, see the greenhouse effect. For day-to-day weather, see what is weather.