From Anisotropy to Omega
  Following the recent measurement of the acoustic peak by the BOOMERanG and MAXIMA experiments in the CMB anisotropy angular power spectrum, many analyses have found that the geometry of the Universe is very close to flat, but slightly closed models are favoured. In this paper we will briefly review how the CMB anisotropies depend on the curvature, explaining any assumptions we could make and showing that this skewness towards closed models can be easily explained by degeneracies in the cosmological parameters. While it is difficult to give independent constraints on the cosmological constant and/or different forms of dark energies, we will also show that combining CMB measurements with other observational data will introduce new and tighter constraints, like $\Omega_\Lambda > 0$ at high significance. 
Alessandro Melchiorri, Louise M. Griffiths