Making a climate footprint assessment can sometimes be difficult. The easy case is when you have one piece of land that produce one product. In those cases, you just sum up all emissions associated with that piece of land, divide with the production and that is the climate footprint per kg of the product.
However, this is seldom the case. In many cases, you get several products from one process. For instance, when you produce milk, you also get meat from slaughtered cows and calves. When you grow wheat you also get straw. So, this is a general problem, most food products are produced on an interconnected web. The question of allocation is essentially how large parts of the emissions should be allocated to each product.
Soybeans are often processed to one fraction of soymeal, which is used as fodder, and soy oil, one of the most widely used cooking oils globally. Let’s assume that 1 kg of soybeans causes 1 kg of CO2-eq emissions. For each kg of soybeans, you get 800 g meal and 200 g oil. The question then is how large emissions does 1 kg of oil or meal cause?
One method is to allocate based on weight. That means that both 1 kg of the meal and 1 kg of oil is assumed to cause 1 kg CO2-eq emissions. But you can argue that what is relevant here is the energy content – that is what makes you full. Soy oil has 6 times higher energy content then meal. If you allocate the emissions based on energy content 1 kg of the meal instead causes only 0,5 kg CO2-eq whereas 1 kg of oil cause 3 kg CO2-eq emissions.
Another way to allocate is based on economic value. It is not necessarily that you want to eat more energy, since that may just make you obese. But you could argue that the price you pay is an indication of the products worth to you. And in contrast to energy content, soy oil costs around twice the price of soymeal. Using economic allocation soymeal cause 0,8 kg CO2-eq, whereas the oil causes 1,6 kg per kg of product.
Regardless of how you allocate the emissions, the total emissions from soy are the same, 1 kg CO2-eq per kg (our assumption). But depending on the allocation method, the responsibility for the emissions varies substantially between allocation methods. There is no strict scientific answer to which allocation method is true. It is a matter of perspective.