Eurostat, the data agency, said Wednesday that the amount of CO2 emissions, a major cause of global warming, are affected by climate conditions, economic growth, population changes, and industrial and transport activities.
Energy efficiency also affects the level of CO2 emissions, Eurostat said.
As such, CO2 emissions would be a very unreliable measure of economic growth, but a growing economy is associated with rising CO2 emissions, because factories are working harder and people, in good times, drive more and hop on planes more often.
Eurostat said CO2 emissions in 2011 were estimated to have dropped 4.1 percent compared to 2010.
The agency said "emissions decreased in nearly all (27) member states, except Malta (plus 6.3 percent), the United Kingdom (plus 3.9 percent), Lithuania (plus 1.7 percent) and Germany (plus 0.9 percent).
The largest decreases were in Belgium and Finland, where CO2 emissions fell 11.8 percent, and Sweden (down 10.1 percent), Denmark (down 9.4 percent) and Cyprus (down 8.5 percent).
Notable declines were also posted by Bulgaria, Slovakia, the Czech Republic, Italy and Poland.