The decrease in pH value of ocean water reported to be caused by global warming can be explained by option 1, which is the larger uptake of CO2 by ocean water.

When the Earth`s atmosphere absorbs excessive amounts of carbon dioxide (CO2) due to activities like burning fossil fuels, deforestation, and industrial processes, it leads to an increase in the concentration of CO2 in the atmosphere. This increase in atmospheric CO2 levels contributes to the greenhouse effect and global warming.

As the surface of the ocean comes into contact with the atmosphere, it absorbs CO2 from the air. This process is called carbon dioxide uptake. However, when there is a larger uptake of CO2 by the ocean water, it causes a chemical reaction that results in the formation of carbonic acid. As a result, the pH of the seawater decreases, making it more acidic.

Ocean acidification, the decrease in pH, has severe consequences on marine life. It can especially harm organisms such as corals, shellfish, and small shelled organisms that rely on calcium carbonate to build their shells and skeletons.

Therefore, option 1, larger uptake of CO2 by ocean water, is the correct explanation for the ongoing decrease in the pH value of ocean water due to global warming