  We show that asymptotically future deSitter (AFdS) spacetimes carry 'genuine'
cosmic hair; information that is analogous to the mass and angular momentum of
asymptotically flat spacetimes and that characterizes how an AFdS spacetime
approaches its asymptotic form. We define new 'cosmological tension' charges
associated with future asymptotic spatial translation symmetries, which are
analytic continuations of the ADM mass and tensions of asymptotically planar
AdS spacetimes, and which measure the leading anisotropic corrections to the
isotropic, exponential deSitter expansion rate. A cosmological Smarr relation,
holding for AFdS spacetimes having exact spatial translation symmetry, is
derived. This formula relates cosmological tension, which is evaluated at
future infinity, to properties of the cosmology at early times, together with a
'cosmological volume' contribution that is analogous to the thermodynamic
volume of AdS black holes. Smarr relations for different spatial directions
imply that the difference in expansion rates between two directions at late
times is related in a simple way to their difference at early times. Hence
information about the very early universe can be inferred from cosmic hair,
which is potentially observable in a late time deSitter phase. Cosmological
tension charges and related quantities are evaluated for Kasner-deSitter
spacetimes, which serve as our primary examples.
