The Grapes of Greenhouse Gas

​“Hey Marg, look at these beautiful grapes I picked up at the market.”
Marg looks up from her laptop: “Grapes?  This time of year?  Where are they from?”
“Er… Lemme see…  California.  Says here on the label.”
Marg looks daggers at me: “You mean those grapes came all the way from California?  Do you realise how much greenhouse gas was spewed into our atmosphere to get them here? We are meant to be decreasing our carbon dioxide emissions.”
Google Assistant pipes into the conversation: “According to tables assembled by the UK Department for Business, Energy & Industrial Strategy (the DBEIS) for 2020, one tonne of long haul airfreight creates 1.13382 kilogram of CO2 equivalent greenhouse gas per kilometre travelled.  The distance from San Francisco to Auckland is 10,487 kilometres, so one kilogram of grapes airfreighted from California creates approximately 11.8904 kilograms of CO2 equivalent greenhouse gas.”
“THANK YOU, GOOGLE!  Marg, it is so creepy the way he listens in on our conversations.”
Marg cracks a smile: “How do you know ‘he’ is a he?  Google could be a ‘she’, you know.  ‘Computer’ is a feminine word in many languages.  And don’t try to change the subject – that 500 grams of grapes you just bought created about 6 kilograms of greenhouse gas.”  That’s probably more than driving the Subaru to Picton.”
Undaunted, Google pipes in again: “Picton is 29.4 kilometres from Blenheim.  Your Subaru makes 11.0 kilometres per litre of petrol and one litre of petrol creates 2.30176 kilograms CO2, so a trip to Picton creates approximately 6.15 kilograms CO2.  About the same.”
“Wow, you’re right, Marg.  That’s a lot more emissions than I expected.  So, does this mean we need to stop buying imported fruits and vegetables?”  
Marg (now with even a bigger smile): “Well, not necessarily.  It depends on how they are transported.  Produce sent on ships creates much lower emissions. 
Google now hits his/her stride: “According to the 2020 UK DBEIS tables, long haul shipping of refrigerated produce creates 0.01308 kilograms CO2 equivalent per tonne-kilometre, or about 1.15 percent of the emissions due to airfreight.  So airfreight spews about 87 times more greenhouse gas than sea-freight to move the same weight of produce the same distance.”
“So, how do we know which imported fruits and vegetables are airfreighted and which are sea-freighted?”
Google: “It has to do with how perishable the produce is.  Importers prefer to send produce by surface because it costs less, but some things won’t last the journey.  According to a 2007 Lincoln University report, most vegetables, including fresh asparagus, green beans, peas and sweet corn tend to be airfreighted, but only a selection of fruits, including cherries, berries, peaches and grapes are airfreighted.  Apples, oranges and bananas are mostly sent by sea-freight.”
“Well, that’s lucky for you, Marg.  You won’t have to give up your fresh banana smoothies.”
Marg, looking serious now: “So, the moral to the story is to buy local fruit and vegetables, when you can.  Buying local also helps our local farmers and businesses during these tough times.  This is what we’re meant to do.”
Google: “But local isn’t always better.  The Lincoln report points out that in some cases, local heated greenhouse vegetables create higher emissions than imported vegetables because coal or natural gas is burned to keep the greenhouses warm and enrich the air inside with CO2 to promote growth.  For example, a 2008 report by AgriLINK NZ states that hot house tomatoes grown with coal heating in Christchurch produce 4.475 kg CO2 per kilogram of tomatoes.  Most of the greenhouses in Marlborough also use coal for heating”.  
“Crikey, that’s almost as high as airfreighted from overseas!  So, what can we eat?”   
Marg smiles: “Well, we could go back to eating only what’s in season.  I grew up eating only fresh fruit and vegetables when they came into season, and it didn’t spoil my childhood.”
“Spoil it? You mean those wild days you spent partying at Tahuna beach when you were a teenager?  You know, I heard about that from some of your friends.  Frankly, I was shocked to hear about it!”
Marg sighs: “Those were the days…”