The North Pacific Gyre Oscillation (NPGO) is a new climate pattern that explains decadal variations in salinity, nutrients, and chlorophyll in the Northeast Pacific. Unlike the Pacific Decadal Oscillation (PDO), which is widely used to explain climate variability in the region, the NPGO is significantly correlated with previously unexplained fluctuations in these oceanic variables. The NPGO is driven by regional and basin-scale variations in wind-driven upwelling and horizontal advection, which control salinity and nutrient concentrations. Nutrient fluctuations drive changes in phytoplankton concentrations, which in turn affect higher trophic levels. The NPGO thus provides a strong indicator of fluctuations in the mechanisms driving planktonic ecosystem dynamics. The NPGO pattern extends beyond the North Pacific and is part of a global-scale mode of climate variability evident in global sea level trends and sea surface temperature. The amplification of the NPGO variance in observations and in global warming simulations suggests that the NPGO may play an increasingly important role in forcing global-scale decadal changes in marine ecosystems. The NPGO is defined as the second empirical orthogonal function (EOF) of sea surface height anomalies (SSHa) in the Northeast Pacific. It is statistically independent of the PDO and is closely related to the "Victoria Mode" index. The NPGO is linked to changes in wind stress, particularly the winds that force coastal upwelling. The NPGO is also associated with changes in nutrient fluxes, which drive fluctuations in chlorophyll-a (Chl-a) and are highly correlated with observed Chl-a. The NPGO is part of a global climate pattern that is symmetric across the equator, suggesting that tropical coupled dynamics are involved in its fluctuations. The observed strengthening of the NPGO mode since 1993 may represent a response to anthropogenic forcing and global warming. This hypothesis is supported by preliminary analyses of climate projections from the GFDL 2.0 coupled climate model, which show an amplification of the NPGO variance by 38% and a reduction of the PDO variance by 58% between the periods 1900–2000 and 2000–2100. If true, the dynamics underlying the NPGO are expected to play an increasingly important role in Pacific-wide ecosystem transitions in coming decades. Further work is needed to explore the utility and implications of the NPGO for understanding past and predicting future global climate and ecosystem change.The North Pacific Gyre Oscillation (NPGO) is a new climate pattern that explains decadal variations in salinity, nutrients, and chlorophyll in the Northeast Pacific. Unlike the Pacific Decadal Oscillation (PDO), which is widely used to explain climate variability in the region, the NPGO is significantly correlated with previously unexplained fluctuations in these oceanic variables. The NPGO is driven by regional and basin-scale variations in wind-driven upwelling and horizontal advection, which control salinity and nutrient concentrations. Nutrient fluctuations drive changes in phytoplankton concentrations, which in turn affect higher trophic levels. The NPGO thus provides a strong indicator of fluctuations in the mechanisms driving planktonic ecosystem dynamics. The NPGO pattern extends beyond the North Pacific and is part of a global-scale mode of climate variability evident in global sea level trends and sea surface temperature. The amplification of the NPGO variance in observations and in global warming simulations suggests that the NPGO may play an increasingly important role in forcing global-scale decadal changes in marine ecosystems. The NPGO is defined as the second empirical orthogonal function (EOF) of sea surface height anomalies (SSHa) in the Northeast Pacific. It is statistically independent of the PDO and is closely related to the "Victoria Mode" index. The NPGO is linked to changes in wind stress, particularly the winds that force coastal upwelling. The NPGO is also associated with changes in nutrient fluxes, which drive fluctuations in chlorophyll-a (Chl-a) and are highly correlated with observed Chl-a. The NPGO is part of a global climate pattern that is symmetric across the equator, suggesting that tropical coupled dynamics are involved in its fluctuations. The observed strengthening of the NPGO mode since 1993 may represent a response to anthropogenic forcing and global warming. This hypothesis is supported by preliminary analyses of climate projections from the GFDL 2.0 coupled climate model, which show an amplification of the NPGO variance by 38% and a reduction of the PDO variance by 58% between the periods 1900–2000 and 2000–2100. If true, the dynamics underlying the NPGO are expected to play an increasingly important role in Pacific-wide ecosystem transitions in coming decades. Further work is needed to explore the utility and implications of the NPGO for understanding past and predicting future global climate and ecosystem change.