The greening of planes, trains and automobiles

Moving goods and people around the world is responsible for a large part of global CO₂ emissions (排放). As the world races to decarbonize everything, it faces particular problems with transportation — which accounts for about a quarter of our energy-related greenhouse gas emissions. Here’s the breakdown of the emissions in 2018 for different modes of transport.

这是2025年高考英语全国卷1（乙卷）阅读理解A的标题和第一段。请问这里的 greening 是什么词性（名词还是动名词）？如何翻译？