  We present results from 3D simulations of the Archean Earth including a
prescribed (non-interactive) spherical haze generated through a 1D
photochemical model. Our simulations suggest that a thin haze layer, formed
when CH4/CO2 = 0.1, leads to global warming of ~10.6 K due to the change of
water vapour and cloud feedback, compared to the simulation without any haze.
However, a thicker haze layer, formed when CH4/CO2 > 0.1, leads to global
cooling of up to ~65 K as the scattering and absorption of shortwave radiation
from the haze reduces the radiation from reaching the planetary surface. A
thermal inversion is formed with a lower tropopause as the CH4/CO2 ratio
increases. The haze reaches an optical threshold thickness when CH4/CO2 ~ 0.175
beyond which the atmospheric structure and the global surface temperature do
not vary much.
