The heat radiated from the Earth. Short-wave solar radiation reaching the Earth does not heat the atmosphere it passes through, but does heat the Earth’s surface. In turn, and particularly on clear nights, much of this heat is radiated out from the Earth. The Earth also absorbs terrestrial radiation reflected from the overlying opaque atmospheric layer. It is by long-wave terrestrial radiation that the atmosphere is heated. Almost one-third of the solar radiation intercepted by Earth is radiated back into space. In urban areas, a reduction in the sky view factor decreases the loss of terrestrial radiation, thereby contributing to the creation of urban heat islands (Grimmond (2007) Geography 30, 3).