<P> The nature of Earth's magnetic field is one of heteroscedastic fluctuation . An instantaneous measurement of it, or several measurements of it across the span of decades or centuries, are not sufficient to extrapolate an overall trend in the field strength . It has gone up and down in the past for unknown reasons . Also, noting the local intensity of the dipole field (or its fluctuation) is insufficient to characterize Earth's magnetic field as a whole, as it is not strictly a dipole field . The dipole component of Earth's field can diminish even while the total magnetic field remains the same or increases . </P> <P> The Earth's magnetic north pole is drifting from northern Canada towards Siberia with a presently accelerating rate--10 kilometres (6.2 mi) per year at the beginning of the 20th century, up to 40 kilometres (25 mi) per year in 2003, and since then has only accelerated . </P> <P> The Earth's magnetic field is believed to be generated by electric currents in the conductive material of its core, created by convection currents due to heat escaping from the core . However the process is complex, and computer models that reproduce some of its features have only been developed in the last few decades . </P> <P> The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically conducting fluids . The Earth's field originates in its core . This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core . The motion of the liquid in the outer core is driven by heat flow from the inner core, which is about 6,000 K (5,730 ° C; 10,340 ° F), to the core - mantle boundary, which is about 3,800 K (3,530 ° C; 6,380 ° F). The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core . </P>

Earth's magnetism is due to which effect