This paper contains a local linear stability analysis for accretion disks under the influence of a global radial entropy gradient \beta = - d \log T / d \log r for constant surface density . Numerical simulations suggested the existence of an instability in two- and three-dimensional models of the solar nebula . The present paper tries to clarify , quantify , and explain such a global baroclinic instability for two-dimensional flat accretion disk models . As a result linear theory predicts a transient linear instability that will amplify perturbations only for a limited time or up to a certain finite amplification . This can be understood as a result of the growth time of the instability being longer than the shear time which destroys the modes which are able to grow . So only non-linear effects can lead to a relevant amplification . Nevertheless , a lower limit on the entropy gradient \propto \beta \approx 0.22 for the transient linear instability is derived , which can be tested in future non-linear simulations . This would help to explain the observed instability in numerical simulations as an ultimate result of the transient linear instability , i.e. the Global Baroclinic Instability .