This is the 573rd most frequent Japanese word.
減少
Reduction; decrease.
Here, '減少' is often used in statistical or monitored contexts to indicate a reduction in measurable quantities over time, such as '人口' ('population' in English), highlighted in the progressing state.
人口が減少しています。
The population is decreasing.
Within this usage, '減少' functions to describe a comparative or descriptive reduction, often highlighting historical data or past studies, related to '生産量' ('production volume' in English).
今年の生産量に比べて、昨年の減少が顕著だった。
Compared to this year's production, last year's decrease was remarkable.
In this sentence, '減少' pertains to environmental or scientific contexts to emphasize a significant decrease in physical quantities, specifically '排出' ('emissions' in English), realized in completion.