Global climate-change trends detected in indicators of ocean ecology

Strong natural variability has been thought to mask possible climate-change-driven trends in phytoplankton populations from Earth-observing satellites. More than 30 years of continuous data were thought to be needed to detect a trend driven by climate change¹. Here we show that climate-change trends emerge more rapidly in ocean colour (remote-sensing reflectance, R_rs), because R_rs is multivariate and some wavebands have low interannual variability. We analyse a 20-year R_rs time series from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite, and find significant trends in R_rs for 56% of the global surface ocean, mainly equatorward of 40°. The climate-change signal in R_rs emerges after 20 years in similar regions covering a similar fraction of the ocean in a state-of-the-art ecosystem model², which suggests that our observed trends indicate shifts in ocean colour-and, by extension, in surface-ocean ecosystems-that are driven by climate change. On the whole, low-latitude oceans have become greener in the past 20 years.