Units for G, g, e, and ef depend on whether the data is
requested in MER or PPP dollars:
For MER, dollars are constant 2015 U.S.
dollars. For PPP, dollars are constant 2017 international dollars.
_P_ and MER values for GDP and related quantities are available
from 1960 onward. PPP values for GDP and related quantities are only available from
1990 onward.
Energy-related values (_E_, _F_, and derived quantities) are
available from 1965 onward.
Note that emissions (_F_, _f_, and _ef_) are reported as millions
of metric tons of carbon dioxide, not carbon.