Future changes in the North American monsoon, a circulation system that brings abundant summer rains to vast areas of the North American Southwest1,2, could have significant consequences for regional water resources3. How this monsoon will change with increasing greenhouse gases, however, remains unclear4,5,6, not least because coarse horizontal resolution and systematic sea-surface temperature biases limit the reliability of its numerical model simulations5,7. Here we investigate the monsoon response to increased atmospheric carbon dioxide (CO2) concentrations using a 50-km-resolution global climate model which features a realistic representation of the monsoon climatology and its synoptic-scale variability8. It is found that the monsoon response to CO2 doubling is sensitive to sea-surface temperature biases. When minimizing these biases, the model projects a robust reduction in monsoonal precipitation over the southwestern United States, contrasting with previous multi-model assessments4,9. Most of this precipitation decline can be attributed to increased atmospheric stability, and hence weakened convection, caused by uniform sea-surface warming. These results suggest improved adaptation measures, particularly water resource planning, will be required to cope with projected reductions in monsoon rainfall in the American Southwest.
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S.P. was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by the University Corporation for Atmospheric Research, Boulder, Colorado and by the NOAA CICS grant - NA14OAR4320106. S.B. acknowledges support from the Caltech Davidow Discovery Fund. The authors thank N. Johnson and H. Zhang for comments on the manuscript.
The authors declare no competing financial interests.
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Pascale, S., Boos, W., Bordoni, S. et al. Weakening of the North American monsoon with global warming. Nature Clim Change 7, 806–812 (2017). https://doi.org/10.1038/nclimate3412
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