Final answer:
Crops can be protected from cold using heaters that blow warm air, which is a common technique in agriculture to prevent frost damage. Spraying water on crops can also be beneficial because the freezing water releases heat. These methods are part of thermal management strategies used in various contexts to protect against cold temperatures.
Step-by-step explanation:
The method that protects crops from colder air involves the use of heaters that blow warm air. This technique is often used in agriculture to preserve the temperature around the plants above freezing, thereby preventing damage from frost. For example, in orchards, water is sometimes sprayed on trees because when the water freezes, it releases heat, which can help to maintain the temperature at or above 0°C, as seen in Figure 14.10 where the icing of trees helps to prevent hard frosts. This counterintuitive strategy is based on the phase change energy release when water turns into ice.
In some extreme cases, like during the Dust Bowl depicted in the provided figure of a farmer and his sons amidst a dust storm, incorrect agricultural practices caused the soil to lose its moisture and structure, leading to disaster. While not directly related to the use of warm air, it underscores the need for effective methods to protect crops from harsh conditions, including colder temperatures.
Furthermore, people, like the snowshoers in the illustration, also use measures such as wearing clothes with low thermal conductivity to conserve heat, which is similar in principle to agricultural techniques that trap warmth to protect against cold. While the contexts differ, the underlying principle of managing thermal energy is consistent across these examples.