[en] We present the first study of the energy dependence of p_t angular correlations inferred from event-wise mean transverse momentum (p_t) fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies √s_NN = 19.6, 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. p_t angular correlation structure suggests that the principal source of p_t correlations and fluctuations is minijets (minimum-bias parton fragments). We observe a dramatic increase in correlations and fluctuations from SPS to RHIC energies, increasing linearly with √s_NN from the onset of observable jet-related (p_t) fluctuations near 10 GeV