Source: AGU Advances
Climate models predict future drying in areas like subtropical southwestern North America, including Arizona and Baja/southern California. However, paleoclimate proxies suggest that this region was in fact wetter than today at the end of the Pliocene warm period, a time often proposed as a potential analogue for a near-future climate. Bhattacharya et al.  present a 3.5 million-year record of leaf wax δD indicating an increase in summer monsoon rains caused by a westward expansion of the North American Monsoon (NAM). Applying an isotope-enabled climate model, they link the stronger monsoon with a diminished east Pacific subtropical-tropical temperature gradient. As similar patterns occur during recent episodes of high NAM rainfall associated with marine “heat waves”, they infer that this mechanism can help explain current monsoon variability and underscore the potential relevance of the Pliocene as an analog for future hydroclimate in this and other regions.
Citation: Bhattacharya, T., Feng, R., Tierney, J. E., Rubbelke, C., Burls, N., Knapp, S., & Fu, M. . Expansion and intensification of the North American Monsoon during the Pliocene. AGU Advances, 3, e2022AV000757. https://doi.org/10.1029/2022AV000757
—Susan Trumbore, Editor in Chief, AGU Advances