A study finds links between a well-known North American climate pattern, external events, and hydroclimatic change over the past millennium. The Pacific North American (PNA) oscillation is an alternating pattern of upper atmospheric pressures that affect the climate in North America and the North Pacific. Atmospheric variability associated with PNA influences regional land and sea surface temperatures, precipitation, and storm tracks. Modern instrumentation has recorded recent PNA phases, but researchers continue to uncover long-term PNA cycles. To document the evolution and environmental impacts of PNA, Gabriel Bowen and colleagues combined 937 years of tree-ring records from different PNA-sensitive regions to reconstruct winter PNA variability. Comporting with previous research, the new reconstruction reveals that the current PNA phase is unprecedented over the past millennium, likely aggravating snowpack decline, drought, and wildfire across parts of the northwestern North America and moderating drought conditions in the southwestern United States. The reconstruction also illustrates that PNA variability correlates with Pacific sea surface temperatures, solar irradiance, volcanic eruptions, and greenhouse gases, and may have played a role in translating these influences into regional patterns of drought and hydroclimate across North America. The authors found that climate models did not adequately simulate the reconstructed record of PNA change, and suggest that climate models may have difficulty predicting future patterns of hydroclimatic change driven by this circulation pattern. - Read at PNAS
Article #16-18201: “Pacific North American circulation pattern links external forcing and North American hydroclimatic change over the past millennium,” by Zhongfang Liu et al.