  We compile a list of 28 independent measurements of the Hubble parameter
between redshifts 0.07 < z < 2.3 and use this to place constraints on model
parameters of constant and time-evolving dark energy cosmologies. These H(z)
measurements by themselves require a currently accelerating cosmological
expansion at about, or better than, 3-sigma confidence. The mean and standard
deviation of the 6 best-fit model deceleration-acceleration transition
redshifts (for the 3 cosmological models and 2 Hubble constant priors we
consider) is $z_{\rm da} = 0.74 \pm 0.05$, in good agreement with the recent
Busca et al. (2012) determination of $z_{\rm da} = 0.82 \pm 0.08$ based on 11
H(z) measurements between redshifts 0.2 < z < 2.3, almost entirely from
BAO-like data.
