  Modern cosmology relies on the assumption of large-scale isotropy and
homogeneity of the Universe. However, locally the Universe is inhomogeneous and
anisotropic. So, how can local measurements (at the 100 Mpc scale) be used to
determine global cosmological parameters (defined at the 10 Gpc scale)? We use
Buchert's averaging formalism and determine a set of locally averaged
cosmological parameters in the context of the flat Lambda cold dark matter
model. We calculate their ensemble means (i.e. their global values) and
variances (i.e. their cosmic variances). We apply our results to typical survey
geometries and focus on the study of the effects of local fluctuations of the
curvature parameter. By this means we show, that in the linear regime
cosmological backreaction and averaging can be reformulated as the issue of
cosmic variance. The cosmic variance is found largest for the curvature
parameter and discuss some of its consequences. We further propose to use the
observed variance of cosmological parameters to measure the growth factor.
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