In terms of total CO2 emissions from a country, identify the correct sequence :

Total (absolute) CO2 emissions of a country are the entire quantity of carbon dioxide it releases in a year, counted as one national sum rather than divided by its population. Almost all of that carbon comes from burning fossil fuel, so the national total tracks the sheer size of a country's energy system: a large, coal-heavy economy can stand at the top of the list even when each of its citizens emits comparatively little.

Applying that measure to the four countries named here, the annual national totals of fossil-fuel and cement CO2 around the reference year of this question (Global Carbon Project estimates for 2013) were:

Arranging those totals from the largest to the smallest gives China > U.S.A. > India > Russia.

Three checks confirm this ordering:

• China's total is close to twice that of the U.S.A., the result of the rapid expansion of Chinese coal-fired power and heavy industry after 2000; that margin is far wider than the uncertainty in the estimates.

• India moved ahead of Russia in the late 2000s, as Indian coal use grew steadily while Russian emissions stayed below their 1990 level, so any ordering that still keeps Russia ahead of India rests on outdated figures.

• Measured per person the ranking is quite different (U.S.A. > Russia > China > India), which is why the stem specifies the total emitted by a country and not the emission per head.

Hence the correct sequence in decreasing order of total CO2 emissions is China > U.S.A. > India > Russia.