The main environmental concern about ocean-based data centers involves the seawater used for cooling. Discharging warm or hot water can potentially affect oxygen levels, pH and marine life in the surrounding waters.

That heat is already apparent at the few seaborne data centers now operating. HiCloud, the engineering contractor for China’s Hainan underwater data center, has reported a temperature increase of less than 1 degree Celsius (1.8 degrees Fahrenheit) in the seawater near the facility. SIN01 in Sines, Portugal, also returns seawater about 1 C warmer.

Many marine species depend on stable water temperatures for breeding, feeding and migration, raising concerns that heat released by multiple underwater data centers could create localized thermal pollution and alter marine ecosystems. And the ocean is already under pressure. UNESCO, the United Nations agency for international cooperation, including in conservation, estimates that about 60% of marine ecosystems are already degraded or used unsustainably.