  A two state model for opinion forming, which has proven heuristic power, is
reviewed with a novel emphasis on the existence or absence of a threshold for
the dynamics. Monitored by repeated small groups discussions floater agents
update their opinion according to a local majority rule. A threshold makes the
initial supports to flow towards eitheir one of two opposite attractors with
only one single opinion. While odd sizes yield a threshold at fifty percent
even sizes, which allow the inclusion of doubt at an opinion tie, produces a
threshold shift toward either 0 or 1 giving rise to minority opinion spreading.
Considering heterogeneous agents like contrarians and inflexibles turn the
dynamics threshold less beyond sone critical values. One unique attractor at
fifty-fifty drives then the dynamics. In addition inflexibles can generate
asymmetry and if one sided they erase the threshold ensuring the associated
opinion to eventually gain the all population support. It may shed a new and
counter intuitive light on some social aspect of the global warming phenomenon.
