When the Environmental Protection Agency announced Wednesday that it would begin regulating airplane emissions, Boeing’s response was, essentially, “Way ahead of you.” The company wants to halve its planes’ CO2 emissions by 2050, and it’s tackling that challenge by using lighter materials, aerodynamic upgrades such as curvy “winglets,” and more efficient engines in its new planes. But the company’s big bet on cutting emissions, particularly in existing planes, is ramping up the use of biofuels.

“The biggest bang for our buck to hit this 2050 goal is right here,” Julie Felgar, Boeing Commercial Airplanes’ environmental strategy director, told reporters ahead of the Paris Air Show. “Can we change the fuel source we’re using or can we change some of it, blend a percent of sustainable aviation biofuel with (conventional jet fuel).”

Boeing is taking an active role in biofuel development; it has projects on six continents attempting to turn algae, camelina, jatropha, and other plants into viable sources of jet fuel. Biofuel burns cleaner than petroleum-based fuels, and the plants that produce it sequester carbon as they grow. But zoom out, and Boeing’s biofuel embrace has to be carefully calibrated for it to actually reduce the company’s net emissions.

Plants are renewable, but whenever they are used for fuel purposes their entire ecological and industrial impact must be considered when determining a carbon footprint. A good example is ethanol, the fuel derived from coal that is blended with gasoline sold at U.S. pumps. When ethanol was first introduced, it was considered an environmental godsend. There’s a lot of corn in the U.S. and, unlike oil, it grows back every year. It appeared a renewable, greener energy source had been found.

But turning corn into fuel takes a lot of energy, and to meet the demand for ethanol, many farmers tore up carbon-sucking, wildlife-supporting grassland to plant more corn. An often-cited 2008 paper in the journal Science explained that corn-based ethanol fuel and its production would actually increase greenhouse gas emissions 47 percent over regular gasoline in a 30-year stretch.

In today’s energy systems, fossil fuels are burned to produce biofuels, and converting native forests or grassland to biofuel cropland in part negates the land’s carbon sequestering effect. Furthermore, biofuel-only crops take farming space away from food-producing crops. The World Resources Institute, an environmental think tank, said in a January report that reliance on biofuels is misguided and could jeopardize land better used for growing food. So if you look only at the combustion and extraction of the fuel, biofuels are better for the environment than petroleum. But extrapolate biofuels’ effects, and it’s not so simple.

That said, Boeing’s biofuel repertoire does have merit. One fuel the company is fond of is “green diesel,” a sustainability-loaded moniker for a fuel derived from vegetable oil. Of of green diesel’s best traits is that it can be produced from waste cooking oil, giving corn, soy, or canola a second use after it’s used to cook corn dogs. Indeed, biofuels made from waste were endorsed in the same World Resources Institute report that decried large-scale plant-based fuel production.

Biofuel’s greatest strength is that it is a “drop-in” replacement, meaning it can be used in engines currently in use. This is important because passenger planes running on the cleanest energy sources such as solar are decades away; the ones running on those fuels now aren’t yet reliable enough to haul passengers from Sea-Tac to LAX. Even when clean fuel sources are perfected, the design and production of a plane line will take years after that.

So we’re nowhere near seeing a Boeing fleet powered by the sun. But, while imperfect, biofuels are a method of cleaning up existing planes, especially if those fuels are created from agricultural waste or crops that don’t bump out existing food stocks.