Publisher Summary This chapter discusses the flux of sensible heat from ecosystems. An ecosystem under strong radiation can respond by using the local air as a heat sink. The chapter addresses the question of how much heat the air can quickly accept or admit as the sensible-heat flux from the ecosystem. A quick response to a sudden loading of an ecosystem by absorbed radiation forestalls brief but damaging increases above the lethal point in cell temperature, which is 45-50°C in many species. Other modes of heat removal also operate in this situation, but without the sensible-heat flux would often be inadequate to prevent overheating, especially when moisture conditions are unfavorable. Sensible heat is translocated within an ecosystem, from soil to leaves, from sun leaves to shade leaves, from the sunny side of a tree to its shaded side, from upper levels to lower. These tiny fluxes help maintain optimum operating temperatures throughout the entire system. The chapter elaborates on the atmospheric environment as a sink or source for sensible heat. Sensible-heat flux density is directly measured by eddy correlation methods in which the temperature of ascending and descending parcels of air and the respective upward and downward speeds are sensed, multiplied to form the individual pulses of sensible heat, and put into storage.