U.S. carbon dioxide emissions are at their lowest levels in 20 years — thanks to the oil and gas industry.

“Oil and natural gas companies are America’s top investors in zero- and low-greenhouse gas emissions (GHG) technologies,” according to a new study released by API (American Petroleum Institute).

“America’s oil and natural gas companies have invested more to reduce greenhouse gas emissions than the federal government and almost as much as all other industries combined,” API Vice President for Policy and Economic Analysis Kyle Isakower said recently in The Maritime Executive. 

The study was conducted by T2 and Associates, and looked at investment in GHG mitigation technology from 2000 through 2012. “During that period, the U.S. oil and natural gas industry directly invested approximately $81 billion in GHG mitigation technologies,” The Maritime Executive reported. “Other U.S. industries invested an estimated $91.2 billion, and the federal government invested an estimated $79.7 billion.”

If you include shale investments, the amount credited to the oil and natural gas industry expenditures on GHG mitigation balloons to $165.4 billion, which is half of the total invested by all industries and the federal government over that time.

Emissions of CO2 in the U.S. have been slowing for years. The Energy Information Administration (EIA) reported last August that “energy-related greenhouse gas emissions in the United States declined in 2011 by 2.9 percent compared to 2010 and an additional 2.1 percent in 2012 compared to 2010.” Last year, emissions were 705 million metric tons below the 2005 level, or 13 percent less, and in fact, “energy-related carbon dioxide emissions have declined in the United States in four out of the last six years.”

And the API suggests that the greenhouse gas reductions achieved by the oil and gas industry are probably understated. “The emission reduction estimates for 2008-2012 presented herein were compiled strictly from company reports,” the institute notes, adding that “there are indications that this summary of reported reductions is an underestimate of actual reductions.”

In other words, the news is almost certainly better than reported because “not all companies reported emission reductions, so the reductions compiled here are likely conservative,” the API said. Reductions in methane emissions reported in EPA’s Natural Gas STAR program “are substantially greater than the total reported here,” and “emissions reductions from substituting natural gas for coal are not included in reported emission reductions by oil and gas companies, but are significant in reducing overall emissions.”

In other words, what was counted is impressive, but there are certainly other reductions that have not been tallied. It’s interesting to note some of the reasons given for declines — and upticks — in CO2 emissions. For instance, America’s GDP grew by 3.0 percent last year, while “emissions increased by 3.9 percent,” which the API attributed to increased use of coal-fired power to do the things that gradually improving economies do. There was a decrease in the nation’s GHG emissions in 2011, “primarily from mild weather and a declining price of natural gas that caused fuel switching away from coal to natural gas in the electric power sector,” as well as federal EPA regulations forcing many to switch from coal to gas to generate electricity.

The interesting thing is that reduced emissions aren’t always the result of investments targeted specifically for that purpose. Most of the investments made by the approximately 650 companies involved in the API study “provide benefits in addition to any ability to reduce greenhouse gas emissions, and were made for multiple reasons including to increase or diversify energy supplies, or to improve efficiency.”Case in point: Of all the investments made by the oil and gas industry which reduced emissions, by far the largest one, $109 billion worth, accounting for 66 percent of the total invested, was in fuel substitution — specifically, expanding shale gas development. Shale gas emits less CO2 than other fuels, but it’s also a lot cheaper.