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Under future climates, leaf temperature (T-l) will be higher and more variable. This will affect plant carbon (C) balance because photosynthesis and respiration both respond to short-term (subdaily) fluctuations in T-l and acclimate in the longer term (days to months). This study asks the question: To what extent can the potential and speed of photosynthetic acclimation buffer leaf C gain from rising and increasing variable T-l? We quantified how increases in the mean and variability of growth temperature affect leaf performance (mean net CO2 assimilation rates, A(net); its variability; and time under near-optimal photosynthetic conditions), as mediated by thermal acclimation. To this aim, the probability distribution of A(net) was obtained by combining a probabilistic description of short- and long-term changes in T-l with data on A(net) responses to these changes, encompassing 75 genera and 111 species, including both C3 and C4 species. Our results show that (a) expected increases in T-l variability will decrease mean A(net) and increase its variability, whereas the effects of higher mean T-l depend on species and initial T-l, and (b) acclimation reduces the effects of leaf warming, maintaining A(net) at >80% of its maximum under most thermal regimes.