Temperature data over the past five decades show faster warming of the global land surface during the night than during the day. This asymmetric warming is expected to affect carbon assimilation and consumption in plants, because photosynthesis in most plants occurs during daytime and is more sensitive to the maximum daily temperature, T max , whereas plant respiration occurs throughout the day and is therefore influenced by both T max and the minimum daily temperature, T min . Most studies of the response of terrestrial ecosystems to climate warming, however, ignore this asymmetric forcing effect on vegetation growth and carbon dioxide (CO 2 ) fluxes. Here we analyse the interannual covariations of the satellite-derived normalized difference vegetation index (NDVI, an indicator of vegetation greenness) with T max and T min over the Northern Hemisphere. After removing the correlation between T max and T min , we find that the partial correlation between T max and NDVI is positive in most wet and cool ecosystems over boreal regions, but negative in dry temperate regions. In contrast, the partial correlation between T min and NDVI is negative in boreal regions, and exhibits a more complex behaviour in dry temperate regions. We detect similar patterns in terrestrial net CO 2 exchange maps obtained from a global atmospheric inversion model. Additional analysis of the long-term atmospheric CO 2 concentration record of the station Point Barrow in Alaska suggests that the peak-to-peak amplitude of CO 2 increased by 23 ± 11% for a +1°C anomaly in T max from May to September over lands north of 51N, but decreased by 28 ± 14% for a +1°C anomaly in T min . These lines of evidence suggest that asymmetric diurnal warming, a process that is currently not taken into account in many global carbon cycle models, leads to a divergent response of Northern Hemisphere vegetation growth and carbon sequestration to rising temperatures. © 2013 Macmillan Publishers Limited. All rights reserved.