What's the Difference between Climate and Weather?
Heading out for a walk on a chilly spring morning, you notice misty clouds on the hills in the distance. You're feeling eager for summer to arrive, but the hillsides are just beginning to green up after the end of winter. You wonder, “Is it cooler than usual this spring? I think I'm usually wearing shorts by this time of year.” Thinking about the weather, you recognize what you're really concerned about is if it will rain on your barbecue this weekend…
These are some of the everyday thoughts people have about weather and climate. Though climate and weather are closely related, they aren't the same thing.
Compare Weather and Climate
The short-term state of the atmosphere—in the past, present, or future—is weather. People describe weather in terms of temperature, precipitation, humidity, cloudiness, wind, and other variables. Weather can vary from minute to minute and location to location. For instance, it's not unusual for a place to have a cloudy, wet morning that gives way to a sunny afternoon, or for rain to fall on one side of a town, but not the other. In order to make sense, descriptions of weather always include both time and location.
Climate is a description of the long-term pattern of weather conditions at a location. The expression “long-term” usually means 30 years or more: climate scientists have agreed that 30 years is a good length of time to establish what the usual range of conditions are at a given location throughout the year.
Looking at three decades of weather records for a place, you might summarize them by saying the summers are hot and humid and the winters as cold and snowy. While these descriptions of climate provide a sense of what to expect in each season, they don't provide any details about what the weather will be on any given day.
Some people have come up with sayings to help explain the difference between weather and climate. Here are a few:
- Climate is what you expect; weather is what you get.
- Weather tells you what to wear each day; climate tells you what to have in your closet.
- Weather is the chocolate caramel truffle, climate is the whole box of chocolates.
How Weather Observations Become Climate Data
Worldwide, scientists observe weather conditions at thousands of stations every day of the year. Some observations are made hourly, others just once a day. Over time, these observations allow us to define what’s normal at each location. Mathematical averages of daily weather conditions (average temperature, average precipitation, and average humidity, for instance) are used to describe a region’s climate.
Climate scientists quantify long-term average conditions for each date of the year by calculating the average (mean) of each parameter (temperature, precipitation, humidy, etc.) over the previous three decades. Official Climate Normals are calculated by NOAA at the start of every new decade. These values are the “normal” against which we contrast our daily weather in order to answer the question: “Is today's weather normal?”
What is the Value of Long-term Record Keeping?
In many locations around the United States, systematic weather records have been kept for over 140 years. These long-term records enable users to detect patterns and trends.
The long-term effort to collect, quality control, and organize data to make it available online serves scientists, natural resource managers and other decision makers, and citizens. One place to find climate data is the Climate.gov Dataset Gallery. The full national climate archive is maintained by NOAA's National Center for Environmental Information.