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The parameterization of convection in climate models is a large source of uncertainty in projecting future precipitation changes. Here an objective method to identify organized low-level convergence lines has been used to better understand how atmospheric convection is organized and projected to change, as low-level convergence plays an important role in the processes leading to precipitation. The frequency and strength of convergence lines over both ocean and land in current climate simulations is too low compared to reanalysis data. Projections show a further reduction in the frequency and strength of convergence lines over the midlatitudes. In the tropics, the largest changes in frequency are generally associated with shifts in major low-latitude convergence zones, consistent with changes in the precipitation. Further, examining convergence lines when in the presence or absence of precipitation results in large spatial contrasts, providing a better understanding of regional changes in terms of thermodynamic and dynamic effects.

Plain Language Summary One necessary condition for a climate model to be judged an accurate representation of the Earth system is that it not only reproduces the correct statistical properties of rainfall but that it does so for the right physical reasons. In other words, evaluating the performance of a climate model must include an evaluation of how well the model represents the dynamical process responsible for precipitation. One such important dynamical process is the triggering and organization of precipitation by long-lived large-scale convergence lines. The current study provides a better understanding of how these precipitation-producing convergence lines, and areas of atmospheric convection more generally, are organized on scales resolved by the models, and how precipitation-producing convergence lines are projected to change in a warmer world. The main result of the work is that because of the strong relationship between organized convergence and precipitation, changes in the organized convergence lines qualitatively account for most of what has been broadly termed the dynamical component of precipitation changes in earlier studies.