In Park et al.(1) we used a coupled climate and silicate weathering model (GEOCLIM) to make the case that emergence of the Southeast Asian islands (SEAIs) played a significant role in cooling Earth’s climate over the past 15 My. The findings were that mountains built through arc–continent collision in the warm and wet tropics enable the geologic carbon cycle to be balanced at lower steady-state pCO2. We acknowledged (1) that Rugenstein et al.’s (2) argument, that increasing marine 87Sr/86Sr over the Neogene is inconsistent with the weathering of juvenile silicate rocks in the SEAIs, could be made. Our explanation was that marine 87Sr/86Sr can be decoupled from globally averaged weathering fluxes of isotopically representative lithologies via the regional weathering of isotopically unique source rocks. We pointed to the variable 87Sr/86Sr of Himalayan lithologies [∼ 0.71 to 1.11 (3)]. Carbonate rocks in the Himalaya (and elsewhere) with high 87Sr/86Sr also represent a significant Sr flux decoupled from silicate weathering and its effects on pCO2 (3). Rugenstein et al.(2) implement a scenario with time-evolving Sr fluxes (but invariant 87Sr/86Sr values) estimating changes in the Himalaya. However, the scenario that they implement has been constructed to fit the 87Sr/86Sr record itself. If one takes a scenario developed to fit a proxy record and then imposes an additional flux not considered in the original fit, it will no longer fit that record. Instead, if one allows Himalayan 87Sr/86Sr values to reach≥ 0.74 for the Pliocene based on data from pedogenic clays (4)[rather than using a fixed value of 0.7214 (2)], the 87Sr/86Sr record can be fit using their model framework. While this approach does not capture the true spatial complexity of evolving tectonic boundary conditions, it illustrates that the record can be satisfied with geologically reasonable fluxes that include emergence of the SEAIs. A similar argument can be applied to the Os record. Regardless of isotopic record interpretations, we know from geologic data that these islands did emerge in the tropics and that the lithologies within them did undergo chemical weathering as they were exhumed. GEOCLIM is spatially resolved in terms of climatology, lithology, and topography and is calibrated to modern CO2 consumption fluxes. Rugenstein et al.(2) use the discrepancy between the scenarios they invoke and the isotopic records to argue that GEOCLIM is not properly representing CO2 consumption through tropical weathering. However, the accuracy of the parameterization of silicate weathering itself is independent of the isotopic flux. The lack of correlation between CO2 consumption and Sr fluxes, both in terms of magnitude and 87Sr/86Sr value (5, 6), makes it difficult to use such data to evaluate silicate weathering models at the regional or global scale. Future efforts to understand the forcings that have influenced long-term climate will need to grapple with the influence of changing and spatially complex tectonic boundary conditions on the evolution of weathering fluxes. Developing additional geological context is critical for moving beyond nonunique zerodimensional geochemical models toward spatial models that more accurately capture geochemical processes. aDepartment of Earth and Planetary Science, University of California, Berkeley, CA 94720; bG éosciences Environnement Toulouse, CNRS, Universit é Paul Sabatier, Institut de Recherche pour le D éveloppement, 31400 Toulouse, France; and cDepartment of Earth Science, University of California, Santa Barbara, CA 93106