Artificial ocean alkalinization (AOA) is investigated as a method to mitigate local ocean acidification and protect tropical coral ecosystems during a 21st century high CO2 emission scenario. Employing an Earth system model of intermediate complexity, our implementation of AOA in the Great Barrier Reef, Caribbean Sea and South China Sea regions, shows that alkalinization has the potential to counteract expected 21st century local acidification in regard to both oceanic surface aragonite saturation Omega and surface pCO(2). Beyond preventing local acidification, regional AOA, however, results in locally elevated aragonite oversaturation and pCO(2) decline. A notable consequence of stopping regional AOA is a rapid shift back to the acidified conditions of the target regions. We conclude that AOA may be a method that could help to keep regional coral ecosystems within saturation states and pCO(2) values close to present-day values even in a high-emission scenario and thereby might 'buy some time' against the ocean acidification threat, even though regional AOA does not significantly mitigate the warming threat.