The rate at which the edge of the advancing ice is wasted depends largely on the climate. If, while the rate of advance remains constant, the climate becomes warmer, melting will be more rapid, and the ratio between melting and advance will be increased. The edge of the ice will therefore recede. The same result will follow, if, while temperature remains constant, the atmosphere becomes drier, since this will increase wastage by evaporation. Were the climate to become warmer and drier at the same time, the rate of recession of the ice would be greater than if but one of these changes occurred. If, on the other hand, the temperature over and about the ice field be lowered, melting will be diminished, and if the rate of movement be constant, the edge of the ice will advance farther than under the earlier conditions of temperature, since it has more time to advance before it is melted. An increase in the humidity of the atmosphere, while the temperature remains constant, will produce the same result, since increased humidity of the atmosphere diminishes evaporation. A decrease of temperature, decreasing the melting, and an increase of humidity, decreasing the evaporation, would cause the ice to advance farther than either change alone, since both changes decrease the wastage. If, at the same time that conditions so change as to increase the rate of movement of the ice, climatic conditions so change as to reduce the rate of waste, the advance of the ice before it is melted will be greater than where only one set of conditions is altered. If, instead of favoring advance, the two series of conditions conspire to cause the ice to recede, the recession will likewise be greater than when but one set of conditions is favorable thereto. Greenland affords an example of the conditions here described. A large part of the half million or more square miles which this body of land is estimated to contain, is covered by a vast sheet of snow and ice, thousands of feet in thickness. In this field of snow and ice, there is continuous though slow movement. The ice creeps slowly toward the borders of the island, advancing until it reaches a position where the climate is such as to waste (melt and evaporate) it as rapidly as it advances.