  The habitable zone is the main tool that mission architectures utilize to
select potentially habitable planets for follow up spectroscopic observation.
Given its importance, the precise size and location of the habitable zone
remains a hot topic, as many studies, using a hierarchy of models, have
assessed various factors including: atmospheric composition, time, and
planetary mass. However, little work has assessed how the habitable zone
changes with variations in background nitrogen pressure, which is directly
connected to the habitability and life bearing potential of planets. Here, I
use an advanced energy balance model with clouds to show that our solar system
habitable zone is about 0.9 to 1.7 AU, assuming a 5 bar nitrogen background
pressure and a maximum 100 percent cloud cover at the inner edge. This width is
about 20 percent wider than the conservative habitable zone estimate. Similar
extensions are calculated for A to M stars. I also show that cooling clouds and
hazes and high background pressures can decrease the runaway greenhouse
threshold temperature to approximately 300 K (or less) for planets orbiting any
star type. This is because the associated increase in planetary albedo enables
stable climates closer to the star, where rapid destabilization can be
triggered from a lower mean surface temperature. Enhanced longwave emission for
planets with very high stratospheric temperatures also permits stable climates
at smaller orbital distances. The model predicts a runaway greenhouse above
approximately 330 K for planets orbiting the Sun, which is consistent with
previous work. However, moist greenhouses only occur for planets orbiting
A-stars.
