[Lonesome in Massachussets]

The earth is estimated to lose about 1,600 metric tons of hydrogen every year through natural means. It will take trillions of years for the earth to lose all its hydrogen, long after the sun burns out. Replacing all energy production with hydrogen fusion (at current rates) would require about 4 metric tons of hydrogen per year. Truly insignificant. For comparison, the mass of the earth is 5,972,000,000,000,000,000,000 metric tons

[Lonesome in Massachussets]

There is roughly 150,000,000,000,000,000 tons of hydrogen in the ocean. Four tons is not even a rounding error.