*We put this to Dr Andy Rice, a Computer Scientist at the University of Cambridge, and Professor David MacKay, Chief Scientific Adviser to the Department for Energy and Climate Change...**Andy Rice* - I think this is quite a good question and what you need to think about is something called "lifecycle assessment". This is basically an idea of trying to think about all the different stages in the production of different goods and services, and what they actually cost the environment.

I had a look around; there aren’t many studies on this for greeting cards, but I did find some work which considers the impacts of newspapers.

The authors of this paper - it was a Swiss study - found that if you have a weekday newspaper, it costs about the same as reading an online one, but with huge amounts of uncertainty and lots of assumptions.

Say, for example, you change the electricity mix - whether you have a lot of fossil fuels in it or not: the online one moves a huge amount. But if you consider food, for example, the difference in footprint between a steak and a risotto is about 200 times the impact of what these authors found the newspaper was.

So, send your Valentine’s card, eCard, physical, and then worry about instead what you choose from the menu on your first date.

*Diana* - There are huge number of variables to consider, but here at the Naked Scientists, we like to go a bit deeper. In fact, we got the author of “Without Hot Air” and Chief Scientific Adviser to the Department for Energy and Climate Change - that’s Cambridge University's Professor David Mackay - to work it out for us. Sadly, he was too busy with his myriad responsibilities to record it, so his answer is voiced by our very own Ben Valsler...

*Ben* - To calculate the energy cost of the eCard, we can add 1 minute of the sender’s computer time, that’s 2 x 100 watts x 60 seconds and that gives 12,000 joules. To be on the safe side, we add another 50% to allow for the internet energy cost, and that gives us a total cost of 18 kilojoules.

Moving on to the paper card, the card itself plus the envelope have a chemical energy of around 0.12 kilowatt hours. An educated guess says that the energy expended at the paper mill is likely to be similar, so that gives us 0.24 kilowatt hours. But then we can expect a fraction to be reclaimed if the card is recycled later. So let’s round down and say the card costs about 0.2 kilowatt hours.

But there’s still the cost of transport to the shop and through the postal system. What is the energy cost of picking up the card from the post box and sending it out across the country?

Sharing equally between the postal items, the collection part of the journey costs 0.01 kilowatt hours per item. Then, the card has to travel a bit further. Let’s say from Lancaster to Skegness via several depots, the answer is 0.009 kilowatt hours. Adding this figure to the collection cost gives roughly 0.02 kilowatt hours, that gives us a total value for the paper card of 0.22 kilowatt hours.

However, the eCard only costs 18 kilojoules, which converts to 0.005 kilowatt hours.

That's on the order of 40 times less.