However, preliminary figures for 2010 indicate emissions were on the rise again with the economic recovery, the agency said Tuesday.
The EEA said the 2009 numbers confirmed an estimate made by the agency last year and were largely due to the economic recession -- but also reflected "sustained strong growth" in the use of renewable energy resources.
EEA Executive Director Jacqueline McGlade noted that greenhouse gas reductions in the EU-27 fell 7.1 percent in 2009 and 6.9 percent for the EU-15 nations.
"Although much of the decrease in greenhouse gases is due to the recession, we are starting to see the results of many EU and member states' proactive policies in renewable energy," McGlade said. "We hope that policy makers continue to build on this success to cut emissions further."
Scientists say gases such as carbon dioxide, methane and nitrous oxide trap heat in the atmosphere and result in a warming of the Earth's climate. Carbon dioxide is released into the atmosphere through the burning of fossil fuels (such as oil, natural gas, and coal), solid waste, trees and wood products.
The EEA's findings indicate some 355 million fewer tons of CO2-equivalent gases were released by EU-27 states between 2008 and 2009. Some 274 million tons fewer were released among the EU-15 states.
One of the biggest decreases was seen in the international aviation and shipping industries, which are responsible for 6.3 percent of total emissions. The reductions in that sector for 2009 equaled 8.6 percent among the EU-27 nations, reflecting the downturn in trade during the depths of the recession.
But, the agency said, the big reductions in emissions aren't likely to be borne out again when the figures for 2010 are determined.
"Verified 2010 emissions from the (EU Emissions Trading Scheme) point to a 3 percent emissions increase over the course of the year, which is still far below pre-recession levels," the environment officials said, adding, "This rebound in emissions partly reflects the economic recovery."
The EEA's release came only one day after the International Energy Agency reported global CO2 emissions in 2010 were the highest in history.
The autonomous intergovernmental organization, based in Paris, said that after 2009's dip, caused by the global financial crisis, emissions are estimated to have climbed to a record 30.6 gigatons last year -- a 5 percent jump from the previous record year in 2008.
"This significant increase in CO2 emissions and the locking in of future emissions due to infrastructure investments represent a serious setback to our hopes of limiting the global rise in temperature to no more than 2 degrees centigrade," IEA Chief Economist Fatih Birol said.
That means it's unlikely the 2-degree limit agreed to last year by international leaders at the Cancun, Mexico, U.N. climate change talks will be feasible, he said.
Under the reductions necessary to meet that goal, total greenhouse gas emissions between 2010 and 2020 must rise less in total than they did just from 2009-10.
"Given the shrinking room for maneuver in 2020, unless bold and decisive decisions are made very soon, it will be extremely challenging to succeed in achieving this global goal agreed (to) in Cancun," Birol said.