  Identifying liquid water on the surface of planets is a high priority, as
this traditionally defines habitability. One proposed signature of oceans is
specular reflection ("glint"), which increases the apparent albedo of a planet
at crescent phases. We post-process a global climate model of an Earth-like
planet to simulate reflected lightcurves. Significantly, we obtain glint-like
phase variations even though we do not include specular reflection in our
model. This false positive is the product of two generic properties: 1) for
modest obliquities, a planet's poles receive less orbit-averaged stellar flux
than its equator, so the poles are more likely to be covered in highly
reflective snow and ice, and 2) we show that reflected light from a
modest-obliquity planet at crescent phases probes higher latitudes than at
gibbous phases, therefore a planet's apparent albedo will naturally increase at
crescent phase. We suggest that this "latitude-albedo effect" will operate even
for large obliquities: in that case the equator receives less orbit-averaged
flux than the poles, and the equator is preferentially sampled at crescent
phase. Using rotational and orbital color variations to map the surfaces of
directly imaged planets and estimate their obliquity will therefore be a
necessary pre-condition for properly interpreting their reflected phase
variations. The latitude-albedo effect is a particularly convincing glint false
positive for zero-obliquity planets, and such worlds are not amenable to
latitudinal mapping. This effect severely limits the utility of specular
reflection for detecting oceans on exoplanets.
