Energy-related carbon emissions have reached their lowest levels since 1991, the U.S. Energy Information Administration (EIA) said in a report.

Carbon dioxide (CO2) emissions from the U.S. energy sector totaled 2,530 million metric tons during the first six months of 2016, which is the lowest in 25 years. The report also projected that energy-related CO2 emissions will decrease to 5,179 million metric tons in 2016. According to the EIA's Short-Term Energy Outlook, mild weather and changes in the country's energy consumption contributed to the decline.

The U.S. had the fewest heating degree days--an indicator of heating demand--during the first six months of the year. Warmer weather during winter months has reduced the demand for heating fuels like electricity, natural gas, and distillate heating oil. As a result, primary energy consumption was 2 percent lower compared with that from the same period in 2015. The decline was more evident in the residential and power sectors, where primary consumption decreased 9 percent and 3 percent, respectively.

In addition, coal and natural gas consumption decreased compared to the same period in 2015. The decrease, however, was greater for coal, which accounts for greater carbon emissions when burned compared with natural gas. Coal consumption declined 18 percent and natural gas consumption fell 1 percent.

Consumption of energy from renewable sources, which do not produce CO2, also increased 9 percent in the first six months of 2016 compared with the same period in 2015. Wind energy accounted for nearly half of the increase, while hydroelectric power, which has increased with the lessening of drought conditions on the West Coast represented 35 percent of the surge in consumption. Solar energy accounted 13 percent of the increase and is expected to see the largest capacity additions of any fuel in 2016, the report said.