Global warming is caused by the burning of fossil fuels. The fertility for Food production has always depended on the carbon cycle. Artificial fertilizers have by-passed this dependence, their production is energy intensive.
The fossil carbon footprint of meat is system dependent. This is especially true of ruminant meat which can be high in feedlot or barley beef at one extreme, however because grassland sequesters carbon, grazing systems can have very low fossil carbon footprints.
In the UK until recent times farming had always involved livestock. From the enclosures and the agricultural revolution in the 1700s farmers maintained fertility to produce crops through the process of crop rotation. Common to all rotational systems was a period of grassland grazed by livestock. This phase increased soil organic matter through carbon sequestration and served to provide some control of weeds and diseases, raising the yields of subsequent crops, then the land went back to pasture and the process rolled on.
With very little in the way of inputs, farms sustainably produced meat, milk and wool, accruing fertility, and grain and vegetables utilising it. Crop rotation and mixed farming created and reliably conserved a range of habitats across the countryside for what we now call farmland wildlife. This could only work because it was carbon neutral.
While mixed farming is still necessary for
organic systems, which by definition are dependent on the carbon cycle rather than high fossil carbon artificial fertilizers, it’s abandonment in conventional agriculture is the principle ‘change in farming practise’ that has led to declines in wildlife in the UK.
All grazing systems generate greenhouse gasses through the carbon cycle, which is natural, and inevitable, their fossil carbon footprint, however, is largely dependent on the amount of artificial fertilizers used in their management.