[emission] more than meets the eye

What is the significance of this picture?

The next most important source of greenhouse gas emissions is methane, particularly from natural gas leaks and off-gassing from rice paddies and flatulent cows (believe it or not). The remainder is a mixture of trace gases, including oxides of nitrogen. [Daniel С Esty and Andrew S. Winston, Green to Gold, How Smart Companies Use Environmental Strategy to Innovate, Create Value, and Build Competitive Advantage, Yale University Press New Haven and London]