Table B1

Changes of magnetic inclination, I, at Leeds, between 2015 and 2020 AD. The first row reports the first-difference estimate from the IGRF-13 model (analogous to formula (4)). The second row reports an estimate obtained by linearising ∂I/∂t in changes in surface magnetic field (similar to Eq. B2). The third and fourth rows show the estimates obtained by integrating geographical sources of change over the CMB and Earth’s surface, respectively (i.e., Eq. (16)).

Quantity	Expression	Value [deg/year]
$\dot{I}$	$\frac{I_{2020}-I_{2015}}{5}$	0.00170109
${\left(\frac{\partial I}{\partial t}\right)}_{\mathrm{LB}}$	$\left[\frac{1}{H{F}^2}\left(B_{\theta }{B}_e{\dot{B}}_{\theta }+B_{\varphi }{B}_e{\dot{B}}_{\varphi }-H^2{\dot{B}}_e\right)\right]$	0.00110045
${\left(\frac{\partial I}{\partial t}\right)}_{\mathrm{GC}}$	${\int }_0^{2\pi }\mathrm{}{\int }_0^{\pi }\mathrm{}\frac{\partial I}{\partial B_c}{\dot{B}}_c\sin \theta \mathrm{d}\theta \mathrm{d}\varphi$	0.00110045
${\left(\frac{\partial I}{\partial t}\right)}_{\mathrm{GE}}$	${\int }_0^{2\pi }\mathrm{}{\int }_0^{\pi }\mathrm{}\frac{\partial I}{\partial B_e}{\dot{B}}_e\sin \theta \mathrm{d}\theta \mathrm{d}\varphi$	0.00110045