Background Paragraph: Carbon dioxide is the most significant long-lived greenhouse gas in Earth's atmosphere. Since the Industrial Revolution anthropogenic emissions – primarily from use of fossil fuels and deforestation – have rapidly increased its concentration in the atmosphere, leading to global warming.  Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid. 
Story: Ben and Andy researched significant greenhouse gasses in Earth's atmosphere. Andy researched more about carbon dioxide, while Ben researched methane gas. 
Question: Which researcher studied another significant long-lived greenhouse gas in Earth's atmosphere?
Ben.