Phytoplankton are microscopic organisms that form the base of the marine food web and are responsible for about half of the oxygen on Earth. Although microscopic, their abundance can be measured by Earth observing satellites because their green pigment, chlorophyll, changes the color of the water. From measurements collected at sea and analyzed for their biological and optical properties, we know there are many thousands of kinds of phytoplankton. Computer models that include ocean biology and physics help us estimate where different phytoplankton types dominate, which affect fisheries and how much atmospheric carbon the ocean can absorb. Future satellites are being designed to monitor global phytoplankton diversity to tell us more about these organisms and how they impact our ocean’s health and our climate. For more information, visit http://climatebits.org.