As nations across the globe negotiate how to reduce their contributions to climate change, researchers at Penn are investigating just how the coming changes will impact the planet. What's clear is that the effect extends beyond simple warming. Indeed, the very physics and chemistry of the oceans are also shifting, and are forecast to change even more in the coming decades.These changes have implications for, among other things, the single-celled organisms that comprise the base of the ocean's food web and are responsible for half of the world's photosynthetic activity: phytoplankton. Not only are phytoplankton sensitive to changes in climate, they also contribute to those changes, as they can remove carbon from the atmosphere and store it deep in the ocean when they die.A micrograph of phytoplankton. Like plants on land, phytoplankton growth is controlled by environmental factors such as light, nutrients, and temperature.