By Sean Mowbray

Environmentalists are getting alarmed that the recent sudden increase in production of renewable diesel (RD), rapid expansion in its applications and unregulated growth could fuel climate change and tropical deforestation.

RD 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.

Experts interviewed for this story said that due to constraints on truly sustainable feedstocks, RD is unlikely to bring anything near the emission reductions needed, and could even intensify the triple crisis of climate change, biodiversity loss, and pollution.

RD can be made from a wide range of feedstocks, including waste vegetable oils, animal tallow, corn, canola (rapeseed), soy, and oil palm. It is often manufactured in retooled fossil fuel refineries using complex biochemical and thermochemical technologies requiring lots of energy, adding to its carbon footprint.

The big selling point for renewable diesel is that it is almost chemically identical to fossil fuel diesel, meaning it can be substituted in existing diesel engines, making it a so-called drop-in biofuel. Biodiesel, by comparison, is made using a far simpler process, not requiring manufacture in an oil refinery and not “drop-in”-ready.

In recent years, renewable diesel production and use have boomed. Global production rose from less than 4 million metric tons in 2014 to 12.45 million metric tons in 2022. This surge could continue in the future, driven by key markets such as the U.S. and the EU.

Neste, a Finnish company and the world’s largest renewable diesel producer, estimates that biofuels, including renewable diesel, could replace 1 billion metric tons of fossil fuels in the transport sector alone.

The potential expansion of renewable diesel across multiple sectors is “terrifying,” Almuth Ernsting, a researcher and campaigner with the NGO Biofuelwatch, says, adding that scaling up RD could lead to huge releases of greenhouse gases due to deforestation and land-use change.

As a biofuel, RD has the potential for lower overall greenhouse gas emissions compared to fossil diesel. That’s due, proponents say, to the use of waste feedstocks, and because CO2 released when the fuel is burned is removed from the atmosphere by growing more feedstock crops — the very definition of renewability. But critics say both claims are oversimplifications, with real-world emissions dependent on many factors.

Industry sources also claim that the carbon intensity of renewable diesel — the total CO2 and other greenhouse gases emitted over the life cycle of a product — is far lower than that of fossil diesel.

But critics argue there isn’t anywhere near the required waste feedstock globally needed to scale up RD production for multiple uses, which means other sources must be tapped. And those other sources, especially soy and oil palm, could bring with them a high carbon cost from land-use change (particularly tropical deforestation), heavy application of petrochemical-based crop fertilizers, other carbon releases incurred when growing a monoculture, and global transport and RD refinery energy consumption.

Without careful carbon accounting for a scaled-up RD life cycle, this miracle biofuel could even risk emitting more carbon than when fossil diesel is burned, say critics.

The attribution of “used cooking oil” is another challenge. It is classified as “waste” by the RD industry, so has minimal carbon impact in modeling. That’s despite the fact that the lion’s share of vegetative and animal “wastes” are not truly waste, but are already claimed by established markets other than biofuels. However, if waste is in short supply, then other crops, with higher life-cycle emissions, will need to be grown to meet surging demand.

The problem, according to analysts: There just isn’t enough used cooking oil or waste animal fats in existence to meet the high projected demand for biofuels like RD, meaning other feedstocks like soy and oil palm are required. Also problematic is that many of these same feedstocks are already under high demand for SAF production.

In 2022, the International Energy Agency warned of a biofuel “feedstock crunch.” In the United States, demand has already “drastically” impacted the global feedstock trade, according to the U.S. Department of Agriculture. Vast amounts of animal fats and vegetable oils are now imported for U.S. RD production and to “backfill” other feedstocks — principally soy oil, which has already become a major renewable diesel feedstock.

Renewable diesel’s problem of scale can only be solved, experts outside the industry say, by siphoning off vegetable oils and other wastes destined for other markets, or by growing vast amounts of alternative feedstocks, and with the conversion of natural lands to crop lands.

That could ultimately lead to major tropical deforestation and carbon releases, while degrading and destroying natural carbon sinks in places like the Amazon or Indonesia to fill sourcing gaps. This land-use change, even if it is indirect, would significantly negate renewable diesel’s high grades for carbon intensity. Land-use changes and agricultural practices are among the biggest contributors to greenhouse gas emissions for biofuels, and the primary reason for varying carbon intensities depending on feedstock.

Multiple industries hooked on fossil diesel are now looking to its “renewable” form as a climate solution, possibly turning a blind eye toward the potential for tropical deforestation and high life-cycle emissions risks.

In Brazil, planned expansion into renewable diesel is causing environmental concern, especially related to deforestation in the Amazon Rainforest and the Cerrado savanna.

The oil and gas sector, lured by alternative-energy financial incentives, are now jumping into the renewable diesel market. Based on an analysis published last year, Chevron, BP, Shell, TotalEnergies and others are planning to refit oil refineries or build 43 biofuel projects capable of producing 260,000 barrels a day by 2030.

The U.S.-based Environmental Integrity Project warns in a report that U.S. biofuel refineries can cause more pollution than fossil fuel refineries when it comes to carcinogenic air pollutants, including acetaldehyde, acrolein, formaldehyde and hexane.

The article was first published by Mongabay: https://news.mongabay.com/2025/05/as-renewable-diesel-surges-sustainability-claims-are-deeply-questioned/