 The growth rate of atmospheric CO2 on inter-annual time scales is largely controlled by the response of land and ocean carbon sinks to climate variability, making it difficult to attribute a reduction in atmospheric CO2 growth rate to CO2 emission reductions induced by a policy change for the near term. Using 100 single model simulations, we find that CO2 emission reductions starting in 2020 are sufficient by 42%, necessary by 31%, and both necessary and sufficient by 22% to cause reduced atmospheric CO2 trends. However, certainty implying sufficient or necessary causation is only reached after 10 and 16 years, respectively. Assessments of the efficacy of CO2 emission reductions in the near term are incomplete without quantitatively considering internal variability. This article was authored by Aaron Spring, Tatiana Iliina, and Yoko Moroski.