Hey, Kevin. I apologize in advance if I seem a little jittery in this response. You see, I've just chugged a huge cup of coffee. I get the beans from a friend in Kenya, who overnights them to me all the way from Africa so they're nice and fresh. It's pure, Grade A stuff. I grind it, roast it and brew it at home with the electricity provided by my local coal-fired plant, and then pour it into a Styrofoam cup. For some reason, the Styrofoam seems to make it taste better (maybe from the chemicals that must leech into it). I'm kidding of course (as far as you know).
You're referring to what environmentalists call food miles or, the distance food travels before reaching your plate (or, in this case, mug). The basic theory goes that the fewer miles between farm and plate, the lower the greenhouse gas impact. Because I don't know what brand of tea or coffee you're drinking, I have no idea how far it traveled (though it probably went a good, long way). Not that it matters too much, because that whole "food miles" thing is a load of (grass-fed, hormone-free) cow manure.
Don't get me wrong as ardent supporters of local agriculture, Dr. Wife, MD and I walk to the local farmer's market to get our produce and cheese. We grow organic vegetables in our garden. And, being the slaves to sustainability we are, we try to stick to locally produced microbrews for our beer. Yet calculating the miles traveled accounts for only a small portion of the carbon-spewing story.
To illustrate: we have some friends who drive 40 miles round-trip in their 20-miles-per-gallon minivan to a local farm to buy a month's worth of meat (which they place in their basement freezer, powered by the coal-fired plant I mentioned above). Think of the carbon footprint they're creating for transporting and storing that measly 10 pounds of beef (which is vacuum-packed in plastic, by the way).
On the other hand, let's say that on the rare occasion when I buy red meat, I bike (or drive my grease-powered car) to the nearby organic market, I get a pound of ground beef that's been trucked from Nebraska in mass quantity. It's hand-wrapped in paper in front of me, and I grill it up on my sustainably harvested wood chip-fired grill that evening. Who's the bigger global warmer in this scenario? And I'm not even taking into account what feed was given to the cattle at the local farm compared to what the herd in Nebraska ate, and the respective land that was used to house each of them. And how do we cow eaters compare to the vegetarian down the street who just ate a tomato organically grown thousands of miles away in Mexico? Far worse, actually. Catch my drift?
Tea and coffee aren't a big problem. Their production is vital to keeping some impoverished Third World villages afloat, and when harvested sustainably they can actually prevent deforestation in these places. They're also shipped by boat, and sea freight creates one-eightieth the carbon footprint of air freight. There's even a tea, called Guayaki Organic Yerba Mate, that its producers claim is carbon negative to drink because it's shade-grown in a South American rainforest and its production gives locals incentive to promote reforestation.
My advice to you is this: be sure to drink sustainably produced, fair trade tea. Buy it loose and in bulk if you can, or in unbleached tea bags, at least. When you go to the store, shop for a lot of groceries at once, and not just for the tea. Does that help? And if you're ever in my neck of the woods, stop by my house and I'll share some of my Kenyan java with you. I've already got a Styrofoam cup here with your name on it.