Model tropical Atlantic biases underpin diminished Pacific decadal variability

Pacific trade winds have displayed unprecedented strengthening in recent decades(1). This strengthening has been associated with east Pacific sea surface cooling(2) and the early twenty-first-century slowdown in global surface warming(2,3), amongst a host of other substantial impacts(4-9). Although some climate models produce the timing of these recently observed trends(10), they all fail to produce the trend magnitude(2,11,12). This may in part be related to the apparent model underrepresentation of low-frequency Pacific Ocean variability and decadal wind trends(2,11-13) or be due to a misrepresentation of a forced response(1,14-16) or a combination of both. An increasingly prominent connection between the Pacific and Atlantic basins has been identified as a key driver of this strengthening of the Pacific trade winds(12,17-20). Here we use targeted climate model experiments to show that combining the recent Atlantic warming trend with the typical climate model bias leads to a substantially underestimated response for the Pacific Ocean wind and surface temperature. The underestimation largely stems from a reduction and eastward shift of the atmospheric heating response to the tropical Atlantic warming trend. This result suggests that the recent Pacific trends and model decadal variability may be better captured by models with improved mean-state climatologies.