The phrase "transient effects" refers to temporary or short-lasting impacts or changes. It means that the effects are not permanent and may only happen for a brief period of time. Full definition
Past school shootings have usually had transient effects on public opinion, if any. (vox.com)
While DNA makes a man, it is the simple transient effects put in to place that create what we call, masculine. (western-project.com)
Such transient effects of environmental factors to which earlier generations were exposed on the expression of characteristics in their progeny illustrate the unique, pliable nature of this epigenetic mechanism. (sciencedaily.com)