# The Carbon Footprint of Milk Production on a Farm
## 3 Results and Discussion
### The CF Range in Milk Production  
The studies under analysis used various units to express the CF of milk production at the farm level, which, in some ways, complicated direct comparisons. The most commonly used unit represents emissions expressed as kg CO\({}_{2}\) eq kg\({}^{-1}\) FPCM, which takes into account the fat and protein contents of milk, thus enabling a better comparison between systems with different milk qualities [5, 22]. Many studies, however, used other units, such as kg CO\({}_{2}\) eq kg\({}^{-1}\) raw milk [49], kg CO\({}_{2}\) eq liter\({}^{-1}\) milk [39], kg CO\({}_{2}\) eq liter\({}^{-1}\) FPCM [42], or even kg CO\({}_{2}\) eq 1000 kg\({}^{-1}\) FPCM [5]. In addition, the emissions per area unit, such as t CO\({}_{2}\) eq ha\({}^{-1}\), were used, which enables the assessment of environmental performance in the context of land use [50]. In certain publications, such as analyses of farms in South America and Africa, emissions were also referred to as livestock units or total net emissions from the farm [2, 51]. The heterogeneity of functional units, in terms of both milk density and quality, is one of the main limitations of a comparative analysis. This hinders a direct comparison of the results and requires the methodological context to be taken into account when interpreting the data. Some authors did not use a standardised FPCM conversion factor, resulting in the need to retain the original units in this review. Based on the analysis of the collected literature, it was determined that the average value of the CF per 1 kg of milk produced on a farm was 1.60 kg CO\({}_{2}\) eq, whereas the 95% confidence interval for the average value ranged from 1.33 to 1.87 kg CO\({}_{2}\) eq (Table 1). Depending on the country, the CF values ranged from 0.78 kg CO\({}_{2}\) eq to 3.20 kg CO\({}_{2}\) eq. The values were characterised by a right-skewed distribution (skewness of 0.88), with the median being lower than the average value and amounting to 1.29 CO\({}_{2}\) eq. A kurtosis close to zero indicated the lack of outliers. The variation coefficient of 40% was at a moderate level; the interquartile range was 0.93 kg CO\({}_{2}\) eq, while the range of variation expressed by the interquartile range was 2.42 kg CO\({}_{2}\) eq. \begin{table}
\begin{tabular}{l c} \hline \hline
**Variable** & **Value** \\ \hline N-Valid (pcs.) & 24 \\ Mean (kg CO\({}_{2}\) eq) & 1.60 \\ Confidence Interval \(-95\%\) (kg CO\({}_{2}\) eq) & 1.33 \\ Confidence Interval +95\% (kg CO\({}_{2}\) eq) & 1.87 \\ Median (kg CO\({}_{2}\) eq) & 1.29 \\ Minimum (kg CO\({}_{2}\) eq) & 0.78 \\ Maximum (kg CO\({}_{2}\) eq) & 3.20 \\ Lower Quartile (kg CO\({}_{2}\) eq) & 1.16 \\ Upper Quartile (kg CO\({}_{2}\) eq) & 2.09 \\ Range (kg CO\({}_{2}\) eq) & 2.42 \\ Interquartile Range (kg CO\({}_{2}\) eq) & 0.93 \\ Variance (kg\({}^{2}\) CO\({}_{2}\) eq) & 0.41 \\ Standard Deviations (kg CO\({}_{2}\) eq) & 0.64 \\ Coefficient of Variation (\%) & 40.00 \\ Standard Error of Mean (kg CO\({}_{2}\) eq) & 0.13 \\ Skewness & 0.88 \\ Kurtosis & 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Descriptive statistics for the carbon footprint for 1 kg of milk production. A study by [PERSON] et al. [50] estimated the average total CF of milk production on small-scale farms in the Colombian department of Boyaca at a level of 1.8 kg CO\({}_{2}\) eq\({}^{-1}\). This value included emissions associated with enteric fermentation (an average of 0.06 kg CO\({}_{2}\) eq\({}^{-1}\)), manure management (0.21 kg CO\({}_{2}\) eq\({}^{-1}\)), and soil nitrification (1.53 kg CO\({}_{2}\) eq\({}^{-1}\)), with the latter component accounting for the largest share of the total CF. The high values were linked to intensive fertilisation and soil management practices. A study by [PERSON] et al. [38] showed that the CF of milk production in Inner Mongolia ranged from 1.5 to 3.4 kg CO\({}_{2}\) eq kg\({}^{-1}\) FPCM, with the main emission-differentiating factors including the nutritional strategy, forage availability, and intensification level.