  The observed value of the cosmological constant poses large theoretical
problems. We find that topology of the Universe provides a natural source for
it. Restricting dynamically an Einstein-Cartan gravity to General Relativity in
our observed Universe allows topological invariants to induce an effective
cosmological constant from dynamical quintessence-like topological fields. Its
evaluation through the boundary of black holes yields a range compatible with
the observed value, with uncertainty of three orders of magnitude. In turns, it
provides a measurement of the Universe's isoperimetric constant.
