  We forecast the ability of future CMB and galaxy lensing surveys to constrain
variations of the fine structure constant. We found that lensing data, as those
expected from satellite experiments as Euclid could improve the constraint from
future CMB experiments leading to a \Delta \alpha / \alpha = 8*10^{-4}
accuracy. A variation of the fine structure constant \alpha is strongly
degenerate with the Hubble constant H_0 and with inflationary parameters as the
scalar spectral index n_s. These degeneracies may cause significant biases in
the determination of cosmological parameters if a variation in \alpha as large
as \sim 0.5 % is present at the epoch of recombination.

Cosmology and Nongalactic Astrophysics