## 5 Discussion  
In the previous sections, several relations between climate control and other domains of livestock production where shown, outlining the central role of climate control in livestock houses. This role may become even more central in future, as shown by the schematization in Figure 4. Climate change will emphasize the importance of climate control of livestock houses since global warming is opening a new long-term challenge: avoiding a perpetual food crisis [87]. Global warming increases the risk of food insecurity by intensifying the heat stress of livestock [81]. By controlling indoor climate conditions, climate-controlled livestock houses are considered resilient buildings that can mitigate the impact of climate change, contributing towards avoiding food crises [88]. As shown in Figure 4, this aspect will be of foremost importance in developing countries. These countries produce more than 50% of meat and 60% of milk that are consumed at a global level [89] and these percentages are increasing due to sociodemographic factors--such as population growth and urbanization--that foster the demand for animal products [90]. To meet this increasing demand and to guarantee the food security of these countries, climate control seems essential because most of the developing countries are in areas characterized by hot climates. Even though many factors--e.g., sanitary problems and quality of local feed--affect the productivity of livestock production in these geographical areas, adverse climatic conditions are among the most limiting factors [89]. In the past, these adverse climatic conditions had a lower impact on productivity because local livestock species were farmed as they easily acclimated to the local climate conditions. Now, the increasing demand for livestock products is turning towards the adoption of high-performance animals, typical of industrial livestock systems, that are imported from developed countries [89]. These animals were genetically selected to increase their productivity, but they are very susceptible to high temperatures due to the strong relationship that exists between production level and metabolic heat production [89]. Hence, mechanical climate control systems may spread considerably in developing countries in future. These systems would contribute towards providing adequate farming conditions, but they would also entail important energy consumption in contexts where the energy supply is often problematic. In addition, this spread of climate-controlled livestock houses would further increase the overall energy consumption of the livestock sector. One of the most urgent and arduous challenges for the future is to develop an energy-efficient climate control that would have positive impacts on all the three areas of sustainability, namely, environment, economy and society [91], as shown in the schematization in Figure 5. An energy-efficient climate control would entail minimum energy consumption to maintain adequate indoor climate conditions and it would integrate energy systems based on low-carbon and renewable energy sources. These features would lead to reducing the resource depletion and to reduce the anthropogenic GHG emissions from the livestock sector, fighting climate change and the improving the environmental sustainability of the livestock sector. The economic sustainability of the livestock sector would also benefit from energy-efficient climate control since a reduction of energy consumption would lead to a consequent reduction of the farm running costs due to energy supply. The adoption of renewable energy sources represents an advantage for farmers since it would decrease their business risks in comparison to fossil fuels. Fossil fuel prices are characterized by important fluctuations that expose farmers to significant business risks and can considerably increase production costs, with a consequent rise of the final product price [19; 92].