Origins of Uncertainty in the Response of the Summer North Pacific Subtropical High to CO₂ Forcing

The variability of the summer North Pacific Subtropical High (NPSH) has substantial socioeconomic impacts. However, state-of-the-art climate models significantly disagree on the response of the NPSH to anthropogenic warming. Inter-model spread in NPSH projections originates from models' inconsistency in simulating tropical precipitation changes. This inconsistency in precipitation changes is partly due to inter-model spread in tropical sea surface temperature (SST) changes, but it can also occur independently of uncertainty in SST changes. Here, we show that both types of precipitation uncertainty influence the NPSH via the Matsuno-Gill wave response, but their relative impact varies by region. Through the modulation of low cloud fraction, inter-model spread of the NPSH can have a further impact on extra-tropical land surface temperature. The teleconnection between tropical precipitation and the NPSH is examined through a series of numerical experiments.