Reduced rainfall over the Amazon basin in an idealized CO2 removal scenario: Remote dynamic processes

Abstract

The Amazon basin plays a crucial role in biodiversity and carbon storage, but its local rainfall is anticipated to decrease under global warming. Carbon dioxide removal (CDR) is being considered as a method to mitigate the impact of global warming. However, the specific effects of CDR on Amazon rainfall have not been well understood. Here, an idealized CDR experiment reveals that the reduced rainfall over the Amazon basin does not recover. Significantly weaker rainfall is found during the ramp-down period compared to the ramp-up period at the same CO2 concentration. This response is associated with the enhanced El Niño-like warming in the tropical Pacific Ocean during the CDR period. This warming pattern has dual effects: weakening the zonal circulation and causing anomalous descent directly over the Amazon basin, while also triggering a stationary Rossby wave train that propagated downstream and generated anomalous ascent over the Sargasso Sea. This anomalous ascent induces anomalous descent and weakens moisture transport over the Amazon basin by the local meridional circulation. Consequently, precipitation is reduced over the Amazon basin in response to the weakened zonal and meridional circulation. Our findings indicate that even if the atmospheric CO2 concentration is lowered, the Amazon basin will remain susceptible to drought. Effective local climate adaptation strategies are urgently needed to address the vulnerability of this critical ecosystem.