The ocean plays an invaluable role in capturing carbon dioxide (CO2) from the atmosphere, taking in somewhere between five to 12 gigatons (billion tons) annually. The biological carbon pump is fueled by tiny plant-like organisms floating on the ocean surface called phytoplankton, which consume carbon dioxide in the process of photosynthesis. A warmer, more acidic ocean could weaken the carbon pump, causing atmospheric temperatures to rise—or it could get stronger, with the opposite effect. “Not only do we not know how big this pump is, we don’t know whether it will remove more or less carbon dioxide in the future. Though the paper’s assessment doesn’t account for the cost of a global research program, Buesseler said that investment would be a small fraction of the $500 billion expected benefit.