  We develop a new and simple method to model baryonic effects at the field
level relevant for weak lensing analyses. We analyze thousands of
state-of-the-art hydrodynamic simulations from the CAMELS project, each with
different cosmology and strength of feedback, and we find that the
cross-correlation coefficient between full hydrodynamic and N-body simulations
is very close to 1 down to $k\sim10~h{\rm Mpc}^{-1}$. This suggests that
modeling baryonic effects at the field level down to these scales only requires
N-body simulations plus a correction to the mode's amplitude given by:
$\sqrt{P_{\rm hydro}(k)/P_{\rm nbody}(k)}$. In this paper, we build an emulator
for this quantity, using Gaussian processes, that is flexible enough to
reproduce results from thousands of hydrodynamic simulations that have
different cosmologies, astrophysics, subgrid physics, volumes, resolutions, and
at different redshifts. Our emulator is accurate at the percent level and
exhibits a range of validation superior to previous studies. This method and
our emulator enable field-level simulation-based inference analyses and
accounting for baryonic effects in weak lensing analyses.
