  Weak gravitational lensing depends on the integrated mass along the line of
sight. Baryons contribute to the mass distribution of galaxy clusters and the
resulting mass estimates from lensing analysis. We use the cosmo-OWLS suite of
hydrodynamic simulations to investigate the impact of baryonic processes on the
bias and scatter of weak lensing mass estimates of clusters. These estimates
are obtained by fitting NFW profiles to mock data using MCMC techniques. In
particular, we examine the difference in estimates between dark matter-only
runs and those including various prescriptions for baryonic physics. We find no
significant difference in the mass bias when baryonic physics is included,
though the overall mass estimates are suppressed when feedback from AGN is
included. For lowest-mass systems for which a reliable mass can be obtained
($M_{200} \approx 2 \times 10^{14}$ $M_{\odot}$), we find a bias of $\approx
-10$ per cent. The magnitude of the bias tends to decrease for higher mass
clusters, consistent with no bias for the most massive clusters which have
masses comparable to those found in the CLASH and HFF samples. For the lowest
mass clusters, the mass bias is particularly sensitive to the fit radii and the
limits placed on the concentration prior, rendering reliable mass estimates
difficult. The scatter in mass estimates between the dark matter-only and the
various baryonic runs is less than between different projections of individual
clusters, highlighting the importance of triaxiality.
