[rajandatta]

Wouldn't it be 694 million metric tonnes? I million megatons is a hell of a lot.

[tasuki]

Probably metric tonnes, but it's weird to use "Mt" to mean metric tonne rather than megatonne. The symbol for metric tonne is "t" [0]. It would certainly be less ambiguous to just spell it out.

[0]: https://en.wikipedia.org/wiki/Tonne