  I present a new technique for the measurement of the growth of cosmic
structures via the power spectrum of weak lensing cosmic shear. It is based on
a template-fitting approach, where a redshift-dependent amplitude of lensing
modulates a fixed template power spectrum. Such an amplitude, which is promoted
to a free parameter and fit against tomographic cosmic shear data, reads
$D(z)\,\sigma_8\,\Omega_{{\rm m},0}=:\Omega\sigma_8(z)$, with $D(z)$ the growth
factor, $\sigma_8$ a proxy for the overall amplitude of the matter power
spectrum, and $\Omega_{{\rm m},0}$ the present-day matter abundance. I show
that this method is able to correctly reconstruct $\Omega\sigma_8$ at the per
cent level across redshift, thus allowing us to measure the growth of
structures unbiased by observing discrete tracers. Moreover, I only makes use
of measurements on linear scales. The method is highly complementary to
measurements of the bias and growth, $b\sigma_8(z)$ and $f\sigma_8(z)$, from
galaxy clustering analysis. I also demonstrate that the method is robust
against an incorrect choice of cosmological parameters in the template, thanks
to the inclusion of an Alcock-Paczy\'nski parameter.
