Harvest is a synonym of Issue. Issue is related to Problem. Problem is a synonym of Catch. Catch is the opposite of Drop. 
Carbon is related to Mass. Mass is related to Land. Land is related to Empire. 
Harvest <--Synonym--> Issue <--RelatedTo--> Problem <--Synonym--> Catch <--Antonym--> Drop 
Carbon <--RelatedTo--> Mass <--RelatedTo--> Land <--RelatedTo--> Empire 