Turns out, bananas are a great example of how shipping food halfway around the world doesn't always mean tons of greenhouse gas emissions. Each banana represents about 80 grams of CO2, according to calculations done by Mike Berners-Lee, author of How Bad Are Bananas? The Carbon Footprint of Everything. Compare that to, say, a kiwi fruit. If grown in New Zealand and eaten in Europe, a kilogram of kiwis represent about 1740 grams of CO2. A kilogram of bananas is 480 grams of CO2.
What makes bananas so carbon cheap?
They are grown in natural sunlight, which means that no energy-intensive hot-housing is required.
They keep well, so although they are often grown thousands of miles from the end consumer, they are transported by boats, which per kilo of freight transported emit only 1% as much CO2 as planes do.
There is hardly any packaging, if any, because they provide their own. (You might sometimes see a bunch in a light plastic bag or wrapper, but this probably pays for itself carbon-wise by reducing the chance of customers ruining the fruit when they try to split a bunch.)
Both kiwis and bananas are shipped long-distance. But what is being grown—and the inputs (fertilizer, pesticide, heat) needed to grow it—often matters as much as where the growing happens. The point: Carbon footprints for food are, unfortunately, not terribly intuitive. To me, this is why we need some standardized system of carbon labeling. Right now, it's all but impossible for individuals to make decisions about the carbon footprint of the things they buy. You shouldn't have to be an expert, or tote a calculator and the proper formulas around with you.
The Guardian: What's the carbon footprint of a banana?