Short-term: hold the freshness
Short-term storage for green tea means protecting what is already there. The goal is not change, it is delay. You are trying to keep the sweet, brothy amino acid character and the green top note for as many months as you can.
That points at one environment and one container: cold, and sealed. A fridge at 0 to 5 degrees Celsius, with the tea in an opaque gasket tin inside a sealed bag, will roughly double the useful life of a green tea compared with a cupboard.
The timeline here is short by design. Three to six months is the realistic window for a green tea at its best. Twelve months is the outer edge even with refrigeration, and by then the top note has usually gone.
So short-term storage is really about buying the right amount. A 50 gram tin that you finish in two months needs no strategy at all. A 250 gram bag that will take you a year needs the fridge, the split, and the sealed bag.
Long-term: change the goal
Long-term storage for green tea is the awkward case, because for almost the whole category the honest answer is that it does not exist. Green tea is made to be drunk fresh, and there is no version of waiting that makes it better.
The one real exception is sun-dried green material, the leaf called dian qing in Yunnan. It is dried in the sun rather than pan-fired, so its enzymes survive, and it is the raw material for raw pu-erh. That leaf does change over decades.
But it stops being green tea the moment you treat it that way. Once it is compressed and put aside for years, everyone calls it raw pu-erh. If you want to age something long-term, buy raw pu-erh. Do not put away a Longjing and hope.
The other honest long-term option is simply not applicable here. Refrigeration extends the window, and it does not open a new one. A green tea in the fridge for two years is a green tea that has been kept, not one that has been aged.
Which is your case
Which case are you in? The test is simple. If you will finish the tea within about three months, you are a short-term storer, and a cool cupboard in a sealed tin is enough.
If it will take you six to twelve months, you are still a short-term storer, but you need the fridge and you need to split the tea so the reserve tin stays shut.
If you are thinking in years, you are in the wrong category. Either buy white or dark tea for that, or accept that you are storing green tea for longer than it was made to last.
And if you have already had a tin for a year and a half, the question is not how to store it. It is whether it is still worth drinking. Smell it, brew a cup, and decide from that rather than from a rule.
A useful way to settle it for yourself is a side-by-side test. Buy two packets of the same tea on the same day, drink one now, and put the other in the fridge for a year. Almost everyone prefers the fresh one.
That experiment costs about the price of a packet and it ends the argument permanently, which no amount of advice about ideal temperatures will do.
A quick decision rule
Here is the decision rule. Buy green tea in 50 or 100 gram lots. If you will drink it within three months, use a cupboard. If not, use the fridge.
Never buy more green tea than you will finish in a year, no matter how good the price is. The discount is not worth a tin of hay.
If you want a tea to lay down, buy white or dark tea instead. That is not a compromise, it is picking the right tool.
And date the tin. Green tea gives you no signal when it starts to decline, and a date is the only thing that will tell you how long it has been sitting there.
None of this is complicated. A tin, a date, and a fridge will handle every short-term case this category has.