For more detailed info about climate variability, check out our Climate Variability page.
Weather varies from one hour to the next, from day to day, and from year to year. We may experience a particularly cool summer one year, and an especially hot summer the next year. Scientists use the term "climate" to express the average weather over a series of years, usually spanning at least a thirty-year period. By taking a thirty-year average, scientists can determine the most likely range of weather conditions in a given place. The typical climate for a place includes factors like the expected temperature through the seasons, the usual amount of precipitation, and the typical wind speed and direction.
Climate also depends on location. Places near the North and South Poles have cooler climates than places near the equator. Locations high in the mountains are cooler than nearby places at lower elevations. Coastal locations usually experience smaller swings in temperature between day and night and between winter and summer than locations that are further inland.
To study global climate change, scientists consider the climate of the whole Earth by taking the average temperature throughout the seasons for all locations around the globe.
Over decades or centuries, the climate in a specific location or around the world can change as well. Both natural and human-influenced factors cause climate change. Because weather varies from year to year, it can be quite challenging to definitively detect changes in climate, even when fluctuations in weather are averaged over 30-year periods as is typically done when defining climate.
How can we be sure global climate is undergoing long-term change, not just a temporary fluctuation? The amount of temperature change and the length of time the temperature has been changing are useful guidelines for determining whether Earth's climate is changing. For example, if warming had occurred over only a few years, there wouldn't be much evidence of a long-term trend. However, global average temperatures have been warming for many decades, so we can be confident that there is a long-term warming trend underway. Also, if the average global temperature had warmed by only a small amount, such as a tenth of a degree, the evidence for a long-term warming trend would be weak. However, the average global temperature has become much warmer over the past century, which is why scientists are confident that climate is changing. The graph below shows warming of yearly global average temperatures since 1880, and the scale of the temperature change is large, which is why scientists have confidence that a significant, long-term change in climate is underway.
Global surface temperature anomaly from 1880 to 2017. Blue lines indicate temperatures that are cooler than the 1901-2000 average, orange lines indicate temperatures that are warmer than the 20th century average.
Credit: UCAR (graphic), NOAA (data)
You can make the activity more sophisticated by assigning a value (amount of temperature increase or decrease) to each card. For example, assign the following values to the heart or diamond (red) cards:
- Ace = 0.1° F temperature rise
- Two = 0.2° F rise
- et cetera through 10
- Ten = 1.0° F rise
- Jack = 1.5° F rise
- Queen = 2.0° F rise
- King = 2.5° F rise
Compute the average global temperature change for the 30-year period. Repeat this several times, taking out four black cards each time.
Modifications for Alternative Learners
This will be quite challenging to students who have difficulty with abstractions. While the activity may be clear, the meaning may be difficult to follow. For these students (and perhaps all students), a constant reminder and connection to the climate data is in order. For example, move around the room and ask students to explain what they've found so far in terms of climate, not cards.
This activity was developed as part of Project LEARN at UCAR.