There are many different formulas for calculating carbon footprint and plenty of organizations offering to undertake the calculations for you. These can vary significantly and therefore give hugely varying results depending which modeling system is used. The larger the focus of calculation the less the variables come to bear. For example calculating the carbon footprint of London commuters or the Steel Industry in the UK over a year can give some indication of carbon emissions. There are so many other factors to calculate that the methodology used for the calculation is just another of those variables and minimized by the scale of the core calculations. To try and calculate the carbon emission from a small order of pens or pencils, yoyo’s or frisbees is really a feel good factor but little else. Getting any meaningful result to a degree of accuracy worth publishing is almost impossible.
If you do come up with a figure, however arbitrary, the next step is often to try and offset it. There are also plenty of organizations offering offset calculators, schemes and packages, again there are many varying ways of assessing what is genuinely offsetting the emissions created.
The focus should be on reducing carbon emissions rather than calculating it or offsetting it. Buy locally and avoid shipping by air if you have to purchase abroad. Reducing or offsetting carbon emissions also doesn’t tackle other important environmental issues, sustainability and recycling for example. A virgin plastic giveaway flown in from China and then “offset” is not as environmentally friendly as a recycled item produced in the UK or mainland Europe and transported by road. Chopping down virgin rainforest and flying it to the other side of the world only to try and offset that impact with a fast growing tree in another country is not a responsible example of sustainable purchasing.
In summary offsetting carbon emissions is not an accurate science that’s helping the environment, it’s as much an appeasement of guilt and arguably it’s allowing buyers and producers to carry on with little or no change to production techniques and transport while “ticking the box”.