Under the right circumstances, Amazon's dream for drone-delivered packages may cut greenhouse gas emissions.

Researchers found four-rotor and eight-rotor drones can outdo delivery trucks when it comes to low emissions, particularly in states like California in which more electrical power comes from renewable-energy sources. The findings are published in a paper published Tuesday in the journal Nature Communications spotted by Axios.

"Although drone-based package delivery faces many technological challenges, safety issues, regulatory concerns and system uncertainties, in this initial estimate we find significant promise in the use of drones to reduce energy use and greenhouse gas emissions in the freight sector compared with traditional pathways," the researchers from Lawrence Livermore National Laboratory, Carnegie Mellon University, SRI International and University of Colorado-Boulder said in the study.

Specifically, in California, drones could deliver small packages weighing about a pound with 59 percent less emissions of greenhouse gases like carbon dioxide. In Missouri, which uses more fossil fuel-based energy to provide the electricity that charges drone batteries, it's only 17 percent.

That's potentially significant, given that trucks cause 24 percent of greenhouse gas emissions from transit, according to the study. Apparently drones might offer more advantages than just speed when it comes to rewriting the rules of package delivery.

But for heavier packages, about 18 pounds, the drone only has 17 percent less emissions than trucks in California, and it has 77 percent more than trucks in Missouri, the study found.