Response to Comment on "Revised paleoaltimetry data show low Tibetan Plateau elevation during the Eocene".

Valdes contest our results, suggesting failings in our modeling approach as well as in our comparison with data. Although their comment points to interesting ideas of improvement, we find that their critique reflects an incomplete understanding of our methods and is not supported by the material they provide.

Neogene cooling driven by land surface reactivity rather than increased weathering fluxes.

The long-term cooling, decline in the partial pressure of carbon dioxide, and the establishment of permanent polar ice sheets during the Neogene period have frequently been attributed to increased uplift and erosion of mountains and consequent increases in silicate weathering, which removes atmospheric carbon dioxide. However, geological records of erosion rates are potentially subject to averaging biases, and the magnitude of the increase in weathering fluxes-and even its existence-remain debated. Moreover, an increase in weathering scaled to the proposed erosional increase would have removed nearly all carbon from the atmosphere, which has led to suggestions of compensatory carbon fluxes in order to preserve mass balance in the carbon cycle.

Revised paleoaltimetry data show low Tibetan Plateau elevation during the Eocene.

Paleotopographic reconstructions of the Tibetan Plateau based on stable isotope paleoaltimetry methods conclude that most of the Plateau's current elevation was already reached by the Eocene, ~40 million years ago. However, changes in atmospheric and hydrological dynamics affect oxygen stable isotopes in precipitation and may thus bias such reconstructions. We used an isotope-equipped general circulation model to assess the influence of changing Eocene paleogeography and climate on paleoelevation estimates.