Lakes play an integral role in the exchange of energy within the Earth system. For instance, lakes can be thought of as storehouses of energy. Specific heat is a measure of how much energy it takes to raise the temperature of one gram of a substance by 1°C. Because the specific heat of water is relatively high, lakes (and other large bodies of water) have the ability absorb a great amount of energy while warming up just a few degrees. During the summer, the water absorbs and stores solar energy; during the winter, the energy stored in the water is gradually released and warms the air.

Lakes are also a part of the hydrologic cycle—the continuous cycling of water between Earth's surface, atmosphere, and biosphere. Liquid water on Earth's surface (such as in lakes, streams, and oceans) evaporates when heated by the Sun; water vapor in the atmosphere condenses to form clouds and precipitation, some of which falls to the ground, replenishing the surface water. Latent heat is the amount of energy released or absorbed when a substance changes physical state. When water vapor condenses in the atmosphere, it releases latent heat, warming the air and helping to drive atmospheric circulation. Transitions between solid, liquid, or gaseous phases require large amounts of energy; for example, it requires about 80 times as much energy to melt ice as to heat liquid water 1°C.

In cold climates, such as in Alaska, lake water freezes as it loses energy to the surrounding air. As a result, ice and snow cover lake surfaces for much of the year. Because snow and ice have high albedos (they reflect more energy than they absorb), they reflect a high percentage of solar radiation back into space. In addition, the ice and snow insulate the lake, minimizing the transport of moisture and energy from the water to the air. The temperature of the water below the ice surface remains within a few degrees above freezing while the snow on the surface can get very cold. Although snow is not a very good conductor, heat is able to flow from the water through the ice and snow to the atmosphere; as the water at the top of the lake freezes into ice, the process releases latent heat that is conducted through the existing ice and snow to the atmosphere. This conductive heat flow is an important source of energy transfer to the atmosphere in the winter.

The formation of lake ice depends on several climate variables, including snow conditions and air temperature. For this reason, evidence of a long-term trend toward decreased lake ice thickness and duration are good indicators of climate change. Students, teachers, and university researchers work together as part of the Alaska Lake Ice and Snow Observatory Network (ALISON) to gather valuable data to learn more about the relationship between lake ice, snow, and climate. In particular, students take measurements of ice thickness, snow temperature gradients (the rate of change in temperature between the top and bottom of the snow, per unit of length), and snow thermal conductivity (which is a measure of how well it conducts heat and is related to its density—for example, dry snow is a poor heat conductor because it has a relatively low density and there is a lot of air between the snow crystals).

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