Belching livestock, decomposing manure and cultivated cropland emitted about 6.6% of Washington’s greenhouse gases in 2017, the Washington Department of Ecology reported Tuesday.

The agriculture sector contributed 6.5 million metric tons to the state’s release of 97.5 million metric tons of gases such as carbon dioxide, methane and nitrous oxide.

Washington’s total output was down slightly from 2016, but remained more than double the state’s aspiration to cut emissions to 45.25 million metric tons by mid-century.

That will require cutting the equivalent of the greenhouse gases emitted by all vehicles, ships, planes and trains, as well as by agriculture.

Still, Ecology said in a statement it was “troubling” that the goal might not be aggressive enough to fight climate change. The department said it will produce before the end of the year a report with new recommendations on cutting greenhouse gases.

“What we’re seeing is that our state’s carbon reduction strategies are beginning to pay off,” Ecology Director Maia Bellon said. “Even with the best economy in the nation, Washington was able to hold the line on emissions, but we need to do more and do it faster.”

Ecology’s report offers a prelude to a more detailed inventory due out early next year on the sources of greenhouse gases. The inventories track progress toward slashing in half by 2050 the emissions released in 1990.

Lawmakers enshrined the aspiration in state law in 2008, promising Washington “will do its part to reach global climate change stabilization levels.”

Agriculture’s output of greenhouse gas emissions has remained fairly steady since 1990, at between 6.3 million and 7 million metric tons. Agricultural emissions in 2017 declined by about 6% from 2016, according to Ecology.

The largest source of emissions attributed to agriculture was the 2.6 million metric tons of methane belched by cattle, sheep and goats.

Decomposing manure released 1.6 million metric tons of methane and nitrous oxide, and farming activities such as tilling and fertilizing emitted another 2.2 million metric tons of greenhouse gases, according to Ecology.

Ecology uses information such as the number of livestock, the amount of fertilizer applied and acres cultivated to make its estimates. The numbers have varied only slightly since 1990.

Emissions from farm equipment fall under the residential, commercial and industrial category.

The transportation sector continues to be the biggest source of greenhouse gases, emitting 43.5 million metric tons in 2017, or 44.6% of the total.

Washington’s greenhouse gases peaked in 2000 at 108.6 million metric tons. The decline of aluminum production and the Great Recession helped cut emissions to 91.8 million metric tons in 2012.

Emissions climbed to 97.6 million metric tons in 2016 before falling to 97.5 million metric tons in 2017.

Ecology attributed the drop to electric utilities investing in renewable energy. Greenhouse gases from coal- and natural gas-fired power plants went down.

Ecology said it anticipated emissions from the electricity sector to continue to decrease. The Legislature this year directed electric utilities to stop supplying energy generated by fossil fuels by 2045.

The Environmental Protection Agency has estimated 2017 U.S. greenhouse gas emissions at 6.45 billion metric tons.