# GFDL - Geophysical Fluid Dynamics Laboratory

Set the temperature change in question, $T$, equal to the sum of a forced part and an internal variability part: $T = T_F + T_I$, with $T_F= \xi T$, so $\xi$ is the fraction of the temperature change that is forced. The assumption is that this is a linear superposition of two independent pieces, so I’ll write the heat uptake as $H = H_F + H_I$.
When the surface of the Earth warms due to external forcing, we expect the Earth to take up heat. But what do we expect when the surface warms due to internal variability? Can we use observations of heat uptake to constrain $\xi$?