Weather is the mix of events that happen each day in our atmosphere. Weather is different in different parts of the world and changes over minutes, hours, days, and weeks. Most weather happens in the troposphere, the part of Earth’s atmosphere that is closest to the ground.
The weather events happening in an area are controlled by changes in air pressure. Air pressure is caused by the weight of the huge numbers of air molecules that make up the atmosphere. Typically, when air pressure is high, skies are clear and blue. The high pressure causes air to flow down and fan out when it gets near the ground, preventing clouds from forming. When air pressure is low, air flows together and then upward where it converges, rising, cooling, and forming clouds. Remember to bring an umbrella with you on low pressure days because those clouds might cause rain or other types of precipitation.
The average weather pattern in a place over several decades is called climate. Different regions have different regional climates. It is the average weather in a place over thirty years. To describe the regional climate of a place, people often tell what the temperatures are like over the seasons, how windy it is, and how much rain or snow falls. The climate of a region depends on many factors including the amount of sunlight it receives, its height above sea level, the shape of the land, and how close it is to oceans. Since the equator receives more sunlight than the poles, climate varies depending on its distance from the equator.
The graph above shows temperature on the Fourth of July in Boulder, Colorado, over several decades. Notice how the white bars stay generally, but not exactly within the range of the average high temperature (87 F) and the average low temperature (56 F).
Credit: Lisa Gardiner/UCAR
However, we can also think about the climate of an entire planet. Global climate is a description of the climate of a planet as a whole, with all the regional differences averaged. Overall, global climate depends on the amount of energy received by the Sun and the amount of energy that is trapped in the system. These amounts are different for different planets. Scientists who study Earth's climate and climate change study the factors that affect the climate of our whole planet.
While the weather can change in just a few hours, climate changes over longer timeframes. Climate events, like El Niño, happen over several years, small-scale fluctuations happen over decades, and larger climate changes happen over hundreds and thousands of years. Today, climates are changing. Our Earth is warming more quickly than it has in the past according to the research of scientists. Hot summer days may be quite typical of climates in many regions of the world, but global warming is causing Earth's average global temperature to increase. The amount of solar radiation, the chemistry of the atmosphere, clouds, and the biosphere all affect Earth's climate.
As global climate changes, weather patterns are changing as well. While it is impossible to say whether a particular day’s weather was affected by climate change, it is possible to predict how patterns might change. For example, scientists predict more severe weather events as climate warms. Also, they predict more hot summer days and fewer extreme cold winter days.
This activity is included in the CLEAN Climate and Energy Resource Collection, a peer-reviewed collection of activities, curriculum, videos, and other tools for teaching.
This activity was developed by Lisa Gardiner at the UCAR Center for Science Education utilizing data from The Weather Channel and based on activities from UCAR Climate Discovery and Project LEARN.