Marine microalgae are vital drivers of Earth's carbon cycle, contributing approximately half of the planet's global primary production and sequestering tens of gigatons of carbon annually through photosynthesis. To survive and thrive in seawater with low carbon dioxide (CO2) levels, these microorganisms depend on specialized and efficient CO2-concentrating mechanisms (CCMs). For years, the regulatory factors that trigger CCM activation have remained incompletely understood—until recent scientific research began to unravel this biological process.