  This paper studies the effect of independent additive noise on the
synchronous dynamics of large populations of globally coupled maps. Our
analysis is complementary to the approach taken by Teramae and Kuramoto
[Teramae and Kuramoto, Phys. Rev. E 63:036210, 2001] who pointed out the
anomalous scaling properties preceding the loss of coherence. We focus on the
macroscopic dynamics that remains deterministic at any noise level and differs
from the microscopic one. Using properly defined order parameters, an
analytical approach is proposed for describing the collective dynamics in terms
of an approximate low-dimensional system. The systematic derivation of the
macroscopic equations provides a link between the microscopic features of the
population (single-element dynamics and noise distribution) and the properties
of the emergent behaviour. The macroscopic bifurcations induced by noise are
compared to those originating from parameter mismatches within the population.
