  In this paper, we investigate the possibility of transient growth in the
linear perturbation of current sheets. The resistive magnetohydrodynamic (MHD)
operator for a background field consisting of a current sheet is non-normal,
meaning that associated eigenvalues and eigenmodes can be very sensitive to
perturbation. In a linear stability analysis of a tearing current sheet, we
show that modes that are damped as $t\rightarrow\infty$ can produce transient
energy growth, contributing faster growth rates and higher energy attainment
(within a fixed finite time) than the unstable tearing mode found from
normal-mode analysis. We determine the transient growth for tearing-stable and
tearing-unstable regimes and discuss the consequences of our results for
processes in the solar atmosphere, such as flares and coronal heating. Our
results have significant potential impact on how fast current sheets can be
disrupted. In particular, transient energy growth due to (asymptotically)
damped modes may lead to accelerated current sheet thinning and, hence, a
faster onset of the plasmoid instability, compared to the rate determined by
the tearing mode alone.
