# Impact of Combine Harvester Technological Operations on Global Warming Potential
## 1 Introduction  
One of today's critical challenges is to meet the needs of a growing human population with limited resources, while prioritizing both global food security and sustainability (based on increasing crop yields) within the context of reducing environmental impacts [1]. Simultaneously, the potential for the efficient use of soil by future generations must be increased [2]. The urgent threat of climate change requires specific action, especially by the main emitters of greenhouse gases (GHGs), like agriculture, which is closely associated with environmental pollution. Agricultural activities are responsible for around 24% of GHGs [3], which often lead to water quality deterioration, wastage of water resources, and loss of biodiversity [4]. According to the latest Food and Agriculture Organization reports on agricultural GHG emissions, the world has almost doubled GHG in the last 50 years, and this amount could increase by another 30% by 2050 [5]. In terms of agricultural technologies, diesel fuels and fertilizers account for most of the energy consumed [6, 7]; furthermore, fertilizers and pesticides have been identified among the most important secondary sources of CO\({}_{2}\) emissions [8]. It is estimated that harvesting accounts for up to 30% of the total cost of using agricultural machinery. Reductions in fuel consumption, air pollution, and the associated costs incurred by farmers [9] can be realized by the optimization of work and the correct operation of combine harvesters (CHs). In 2017, the global agricultural sector produced CO\({}_{2\text{eq}}\) emissions of 11.1 gt year\({}^{-1}\)[10], with Lithuania alone responsible for 4387.0 kt year\({}^{-1}\)[11]. As an EU member state, Lithuania participates in the global climate change mitigation process, contributes to EU commitments, prepares national documents, participates in the formation of climate change policy, and is one of the 195 countries that have ratified the United Nations Framework Convention on Climate Change. Rapidly increasing concentrations of atmospheric GHGs, including CO\({}_{2}\), CH\({}_{4}\), and N\({}_{2}\)O, are contributing to unprecedented changes in the earth's atmosphere. Collectively, these three GHGs account for over 90% of anthropogenic global warming [12]. GWP is a widely used, convenient, and quantifiable measure of environmental impacts. Thus, this paper uses GWP as a clear indicator of the unified concept. It should be noted that the impact of CH exhaust gases on GWP is primarily influenced by the direct use of diesel fuel and its conversion to CO\({}_{2}\) within internal combustion engines. Other emissions, including N\({}_{2}\)O and CH\({}_{4}\), can be reduced by different engine technologies, (e.g., clean-up catalysts, NO control by selective catalytic reduction [13], and CO/HC emissions control by diesel oxidation catalysts), and a direct correlation has been noted between CO\({}_{2}\) emissions and fuel consumption. In order to reduce engine emissions, the following engine improvement systems can also be useful: cylinder shut-off [14; 15], start-stop [16; 17], and speed reduction [18; 19]. Emissions can also be reduced by switching to alternative fuels, such as compressed natural gas (LNG) and liquefied petroleum gas (LPG) [20], or by installing electric hybrid engines into the agricultural machinery [21; 22; 23]. However, overall, emissions can only be reduced if less fuel is used [24; 25; 26]. Other researchers are also looking at ways to reduce fuel consumption and air pollution when harvesting with CHs [27; 28]. In their 2019 research, [PERSON] et al. revealed that leaving longer-length stubble in the field when harvesting is an acceptable way of reducing fuel consumption (and thus emissions) while preserving the driving speed. They achieved a reduction in hourly fuel consumption of 6.2 l h\({}^{-1}\), which in turn resulted in 16.3 kg h\({}^{-1}\) less CO\({}_{2}\), by increasing the stubble height of oilseed rape from 0.2 to 0.4 m (equating to 7 t h\({}^{-1}\) less stem mass being fed into the CH).