Renewable diesel is a biofuel made from vegetable oils and animal fats touted by proponents as an almost miraculous “drop-in” transition fuel able to drastically cut greenhouse gas emissions while easily replacing fossil diesel in all manner of engines. But this biofuel’s recent sudden surge in production and rapid expansion in applications is alarming environmentalists, who warn unfettered growth could fuel climate change and tropical deforestation. Renewable diesel, or RD, can be made from a wide range of feedstocks, including waste vegetable oils, animal tallow, corn, canola (rapeseed), soy and oil palm. The feedstock used, where and how it is produced, and whether forests are felled to make way for biofuel crops, all determine RD’s carbon emissions as compared to fossil diesel. RD is often manufactured in retooled fossil fuel refineries using complex biochemical and thermochemical technologies requiring lots of energy — adding to its carbon footprint. Chevron, BP, Shell and other major fossil fuel companies are now converting excess refinery capacity to make RD and enter the market in a big way. A freight train in the U.K. run on renewable diesel. Replacing red diesel (fossil diesel specifically earmarked for rail or agricultural vehicles) with RD can cut a train’s emissions by “as much as 90%,” according to the industry. But such claims can be erroneous since some feedstocks have high carbon intensity (such as oil palm) over others (like used cooking oil). Image by Rob Reedman via Flickr (CC BY-NC-ND 2.0). A big selling point for renewable diesel…This article was originally published on Mongabay