Charge density modulations have been observed in all families of high-critical temperature ( ) superconducting cuprates. Although they are consistently found in the underdoped region of the phase diagram and at relatively low temperatures, it is still unclear to what extent they influence the unusual properties of these systems. Using resonant x-ray scattering, we carefully determined the temperature dependence of charge density modulations in YBa Cu O and Nd Ba Cu O for several doping levels. We isolated short-range dynamical charge density fluctuations in addition to the previously known quasi-critical charge density waves. They persist up to well above the pseudogap temperature , are characterized by energies of a few milli-electron volts, and pervade a large area of the phase diagram.