Differences Between Climate and Weather

Copyright Information - Modified with permission from Global Climates - Past, Present, and Future, S. Henderson, S. Holman, and L. Mortensen (Eds.), EPA Report No. EPA/600/R-93/126. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC, pp. 1 - 6.

Understanding and interpreting local weather data and understanding the relationship between weather and climate are important first steps to understanding larger-scale global climate changes. In this activity, students will undertake a project that allows them first hand knowledge of local weather changes and how that relates to local climates.

Background

When atmospheric scientists describe the "weather" at a particular time and place or the "climate" of a particular region, they describe the same sort of characteristics: air temperature, type and amount of cloudiness, type and amount of precipitation, air pressure, and wind speed and direction. Why do they both describe similar characteristics? And why do we eagerly listen to the local weather forecaster but pay far less attention to predictions from the state climatologist?

Weather is the current atmospheric conditions, including temperature, rainfall, wind, and humidity at any given place. If you stand outside, you can tell how hot it is by taking a temperature reading or feel if it is raining or windy, sunny or cloudy. All of these factors make up what we think of as weather. Weather is what is happening right now or likely to happen tomorrow or in the very near future.

Climate, on the other hand, is the general weather conditions. For example, in the winter, we expect it to often be rainy in Portland, Oregon, sunny and mild in Phoenix, Arizona, and very cold and snowy in Buffalo, New York. But it would not be particularly startling to hear of an occasional January day with mild temperatures in Buffalo, rain in Phoenix, or snow in Portland. Meteorologists often point out that "climate is what you expect and weather is what you get." Or, as one middle school student put it, "Climate helps you decide what clothes to buy, weather helps you decide what clothes to wear."

Climate is sometimes referred to as "average" weather for a given area. The National Weather Service uses values such as temperature highs and lows and precipitation measures for the past thirty years to compile "average" weather for any given area. However, some atmospheric scientists consider "average" weather to be an inadequate definition. To more accurately portray the climatic character of an area, variations, patterns, and extremes must also be included. Thus, climate is the sum of all statistical weather information that helps describe a place or region. Climate can be applied more generally to large-scale weather patterns in time or space (for example, an Ice Age climate or a tropical climate).

To investigate how climate may be changing due to human influences, scientists use weather data from as far back as the historical record goes, as long as the data are accurate. Detailed daily weather data are collected at surface meteorological stations (weather stations) throughout the world. However, several factors can limit the accuracy of the data. For example,

• Many stations are in or near urban areas, which often experience warmer temperatures than the surrounding rural land. This is due to the heat absorbing properties of concrete and asphalt and the lack of shade and evaporative cooling from vegetation. This phenomenon is known as the "heat island effect."
  
  
• Many weather stations have been moved from rural locations to airports, making it difficult to interpret and compare measurements over time.

Understanding and interpreting local weather data and understanding the relationship between weather and climate are important first steps to understanding larger-scale global climate changes.

Learning Goals

1. Students will understand the general distinctions between weather and climate.
   
   
2. Students will understand that daily weather measurements are highly variable compared to long-term climate data.
   
   
3. Students will appreciate the difficulty of identifying climate trends based on limited data.
   
   

Alignment to National Standards

National Science Education Standards

• Earth and Space Science, Structure of the Earth System, Grades 5 to 8, pg. 160, Item #10: "Global patterns of atmospheric movement influence local weather. Oceans have a major effect on climate, because water in the oceans holds a large amount of heat."

Benchmarks for Science Literacy, Project 2061, AAAS

• The Physical Setting, The Earth, Grades 9 to 12, pg. 70, Item #3. "Weather (in the short run) and climate (in the long run) involve the transfer of energy in and out of the atmosphere. Solar radiation heats the landmasses, oceans, and air. Transfer of heat energy at the boundaries between the atmosphere, the landmasses, and the oceans results in layers of different temperatures and densities in both the ocean and atmosphere. The action of gravitational force on regions of different densities causes them to rise or fall - and such circulation, influenced by the rotation of the earth, produces winds and ocean currents."
  

Grade Level/Time

• Grade level: 6 to 8
  
  
• Time
  
  
  • Teacher instructions and introduction: 30 minutes
    
    
  • Student data collection: 50 minutes per week
    
    
  • Analysis and discussion as class: 45 minutes
    
    

Materials

• Local weather information from newspaper or Web source
  
  
• Data charts
  
  
• Colored pencils
  
  

Procedure

1. Determine how long you want students to collect weather data for (a month, three months, or all year). One month of data collection is usually sufficient to effectively illustrate weather variation, but longer-term data collection enables discussion of seasonal changes.
   
   
2. Determine what weather data you want students to collect (for example, daily high and low temperature, normal high and low temperature, record high and low temperature, daily precipitation, or normal precipitation).
   
   
3. Have the students prepare graphs to record data (the detail of the graphs depends upon the duration of your weather data collection and the data that you choose to include). You may wish to have the students post their graphs around the room and add data to them periodically.
   
   
4. Have students begin to collect data (don't forget weekends) by clipping weather data from a newspaper or checking with an on-line source. Record this information in a notebook.
   
   
5. Either daily or weekly, have students record each day's weather data on the graph. Be sure to record the average or "normal" values. The comparison between the average and daily weather data will form the basis for the discussion of the differences between weather and climate.
   
   
6. In a class discussion, ask the students to compare daily weather data to the "normal" or "average" data. What features do they observe? Lead the students to discuss the differences between weather and climate that they can observe in their charts. Discuss the following questions:
   
   
   • For any of the weather data, which line on the graph is more variable: the daily values or the average values? Why?
     
     
   • If you were asked to predict the weather for tomorrow from the data shown on the graph, what data would you find the most useful: the daily or average values?
     
     
   • If a scientist reported that last month in your state was warmer than the same month a year ago, would you consider this to be evidence for climate change? Why or why not? What kind of data would be the most convincing: changes in short-term (daily, weekly, or monthly) weather, or changes in longer-term climate data?
     
     
   • Based on the data that the class has collected, does this year appear to be warmer, cooler, or about the same as the average? From this data, what, if anything, can you conclude about climate change?
     
     
7. In addition to collecting and graphing local data, consider doing this exercise in cooperation with another school (or schools) in a completely different geographic location. Classes could exchange data with each other for comparison and discussion. Telecommunication techniques would enhance the links to other schools.
   
   

Assessment Ideas

1. As formative assessment, it is critical to continue to question students about why they are collecting the data and what they are seeing in the data during the exercise. If they are conducting data for a month, you may need to remind students of the goals of the exercise.
   
   
2. Create your own simulated weather datasets. Ask students to examine a dataset and answer the first two questions above.
   
   

Modifications for Alternative Learners

• Pairing for this exercise would benefit students who have difficulty with visual interpretation of data.