Energy left over from the original formation of the planet along with heat from radioactive decay slowly escapes from within the Earth every day. In some areas where the increase in temperature with depth is high enough, this geothermal energy can be used to generate electricity, but is limited to only a few locations worldwide and faces technical challenges. Another form of geothermal energy is using the Earth's relatively constant subsurface temperature via heat pumps for heating and cooling buildings, which can reduce other energy needs for temperature regulation but cannot produce electricity.