Biomass is an energy source derived from organic material such as animal or plant matter and it is growing in popularity. Proponents increasingly favour biomass use over fossil fuels due to the low levels of carbon emitted when the material is burned, and see it as the answer to fighting climate change.

However, though it is classed as renewable, questions have been raised over just how green it really is, with fears that its predominant reliance on felling and burning trees as a replacement for fossil fuels could do more harm than good.

What are the benefits?

As countries struggle to maintain the clean air targets set in the 2015 Paris Agreement, consumers and energy companies are increasingly seeking green alternatives to traditional energy production methods, including biofuels. According to Carbon Brief, since the last European directive on renewables in 2008, bioenergy has provided around half of the growth in the renewables sector.

A 2016 report from World Energy Resources found that final energy from biomass is about 50 EJ of energy – equivalent to 14% of the world’s final energy use – though the potential for final energy from biomass worldwide is far higher, and could be as much as 150 EJ by 2035.

Biomass is an incredibly versatile substance, able to produce energy through being burned directly, converted into liquid biofuels or harvested as a gas from landfills or anaerobic digesters. Its own source of energy comes from the sun, and as plant matter can be regrown relatively quickly, it is classed as renewable.

While a number of waste materials can be used to create biomass – such as sawdust from lumber mills, crop residue, and even chicken litter – it is predominantly sourced from wood. This practice is deemed sustainable by biomass advocates as it can utilise by-products of forest management or help to clear dead or sick trees from an area.

The US Forest Service Wood calls wood an “abundant, sustainable, homegrown cellulosic resource”, adding that it could “significantly contribute to meeting 30% of US petroleum consumption from biomass sources by 2030”. In 2016, biomass made up 4.8% of total US energy consumption and 12% of renewable energy in the country.

However, critics warn that an over-dependence on a process involving burning trees could have a dangerous effect.

What are the negatives?

In a blog for Carbon Brief, Professor John Beddington, the UK government’s chief scientific adviser between 2008 and 2013, wrote that it “may even lead to a situation whereby global emissions [of carbon dioxide] accelerate”, saying we should instead focus our attentions on developing the less damaging sources of wind and solar.

He warns that encouraging the use of bioenergy may lead people to harvest trees and plants specifically for use in power plants rather than merely using the waste products, a fear which will become increasingly likely as demand for biomass grows.

In addition, he notes that burning biomass is not even an entirely clean process, saying wood’s lower burning temperature combined with its greater carbon intensity “means wood releases more carbon than fossil fuels per unit of energy generated (almost 4 times more than natural gas, and over 1.5 times that of coal)”.

The Earth Institute similarly found current biomass-burning power plants produce 65% more carbon dioxide per megawatt hour than fossil fuel plants, saying it also contributes large amounts of air pollution such as nitrogen oxides, carbon monoxide and lead, many of which are carcinogenic.

As such, critics say the use of biomass should not be welcomed wholesale as a carbon-neutral alternative to coal but instead be approached as a source to be developed with caution, with more transparency about any potentially negative environmental impact essential for consumers.