Columbia subject headings:
Harvard subject headings:
Capitalism--Environmental aspects--History--21st century.
Communism and ecology--History--21st century.
Environmental policy--History--21st century.
Socialism--Environmental aspects--History--21st century.
Princeton subject headings:
Capitalism--Environmental aspects--History--21st century.
Communism and ecology--History--21st century.
Environmental policy--History--21st century.
Socialism--Environmental aspects--History--21st century.