The obvious threat is that warming waters - those in the north are warming fastest - will destabilise the hydrates releasing vast amounts of methane and thus accelerating climate change. This is a particularly scary possibility for three reasons:
- It's a positive feedback loop. Once established it will probably overwhelm all the other mechanisms.
- The sea warms slowly and warming lags the relevant gas releases.
- Hydrate deposits are poorly understood so we can't forecast how much methane will be released how soon.
Hydrates also have a promise. Methane is a very clean fuel and its extraction from hydrates will probably be an efficient process. IF we switched from coal and oil to methane and IF we could keep leakage well below 1% then we would reduce the greenhouse effect. It's no panacea but it would help a lot.
Those are big IFs. In practice new energy sources usually add to consumption. The US currently benefits from fracked methane but instead of closing coal mines it is exporting coal - much of it to Europe.
In a sane world hydrates might be an opportunity. In fact they remain a dreadful threat.