  Atmospheric ozone plays an important role on the temperature structure of the
atmosphere. However, it has not been included in previous studies on the effect
of an increasing solar radiation on the Earth's climate. Here we study the
climate sensitivity to the presence/absence of ozone with an increasing solar
forcing for the first time with a global climate model. We show that the
warming effect of ozone increases both the humidity of the lower atmosphere and
the surface temperature. Under the same solar irradiance, the mean surface
temperature is 7 K higher than in an analog planet without ozone. Therefore,
the moist greenhouse threshold, the state at which water vapor becomes abundant
in the stratosphere, is reached at a lower solar irradiance (1572 Wm^-2 with
respect to 1647 Wm^-2 in the case without ozone). Our results imply that ozone
reduces the maximum solar irradiance at which Earth-like planets would remain
habitable.
