What is our assessment?

Based on our analysis, improving district heating for industry by integrating low-carbon heat sources has the potential to significantly reduce the use of fossil fuels and the emissions they generate. However, the lack of data, combined with the complexity of such projects and the growing interest in alternative decarbonization pathways, makes this a potential solution to “Keep Watching.”

What is it?

District heating systems consist of a network of underground pipes that distribute heat to a large number of buildings, including industrial buildings. In the industrial sector, district heating is used by light industries and for processes such as drying, paper making, food processing, as well as space heating and even heat-driven chillers for refrigeration. Industry is well-suited to district heating because it typically has steady and predictable heat demand throughout the year. Current district heating systems rely heavily on coal and natural gas for heat generation, often as part of combined heat and power generation. Low-carbon alternatives for district heating can include electric heat pumps, solar thermal, deep geothermal, and even waste heat from other industries. 

Does it work?

Shifting district heating for industry from conventional heat sources to low-carbon heat sources will significantly reduce emissions. Our analysis for district heating use by commercial and residential buildings shows that significant emissions can be avoided by shifting to electric boilers, heat pumps, and the use of waste heat (see Improve District Heating: Buildings). Similar outcomes are likely possible for industrial district heating use, and emissions reductions will increase as more renewables are integrated into the electricity systems used to power electric boilers and heat pumps. 

Why are we excited?

District heating for industry currently produces significant emissions. According to the International Energy Agency (IEA), district heating for all applications accounted for 4% of global emissions in 2022, and roughly 40% of the heat energy from district heating was delivered to industry. China is a major adopter of district heating for industries, with the combustion of coal supplying much of that heat. The shift to renewable heat sources is likely to increase because both China and the EU have policies targeting the adoption of renewables in district heating. Because district heating systems serve multiple buildings, a single project to replace fossil fuels with renewables can have a large impact. Such projects also have the benefit of reducing local air pollution. 

Why are we concerned?

Although simple on paper, replacing fossil fuel systems with lower-carbon alternatives in district heating systems can be an extended undertaking involving many stakeholders and years of planning. Some low-carbon options may not be suitable for industrial processes that require higher temperatures than those needed for space heating. There is also a significant lack of publicly available data about how industry currently uses district heating and the opportunities and challenges involved in shifting to renewables. In the meantime, industrial heat pumps with higher temperature outputs (100–200°C) are increasingly available and could become a low-carbon competitor to the use of a conventional district heating system.

What is our assessment?

Based on our analysis, bio-blocks offer a promising pathway for long-lasting storage of already-captured biogenic carbon, and could meaningfully scale using existing technologies and low-cost plant biomass. However, little is known about their real-world performance over long time scales, effectiveness depends on storage conditions, and land use impacts remain uncertain. As a result, we will “Keep Watching” Bury Bio-Blocks. 

What is it?

Bio-blocks are dried and compressed plant matter, typically forestry or agricultural residues, enclosed in a non-polluting, impermeable barrier for long-term carbon storage. To make carbon-storing bio-blocks, plant residues are dried to moisture levels low enough to prevent rotting driven by microorganisms, mechanically compressed into dense blocks, and encased inside multi-layer barriers that keep out water and oxygen (Crotty et al., 2026; Yablonovitch & Deckman, 2023; Zeng et al., 2023). The barriers often combine nontoxic geomembranes made of high-density or linear low-density polyethylene liners, compacted clay layers, and polymeric sealants (Yablonovitch & Deckman, 2023). Once packaged, the bio-blocks are buried in designated sites designed to keep the material dry and sealed so the stored carbon cannot return to the atmosphere (Amelse, 2025). The block-making process does not make carbon inert, but “locks” it into the organic matter. Bio-blocks can be made from many types of biomass, making them a versatile means of storing biomass carbon (Allen, 2025).

Does it work?

Bio-blocks are a physically plausible means to durably store carbon captured by plants. Microbes cannot sustain metabolism when water activity is below 0.60, preventing biomass decomposition in dry, oxygen-deprived storage (Crotty et al., 2026; Yablonovitch & Deckman, 2023). Bio-blocks’ net climate benefit depends on processing emissions, biomass type and source, and whether they remain dry and intact. Effectiveness is supported by peer-reviewed studies, concept papers, life-cycle analyses, and reactor studies (Crotty et al., 2026; Johnson et al., 2025; Wang et al., 2011; Ximenes et al., 2019), with the strongest support from wood vaulting, engineered dry biomass storage, and landfill-style wood preservation (Crotty et al., 2026; Yablonovitch & Deckman, 2023; Zeng & Hausmann, 2022). A 3,775-year-old wood sample found 2 meters below ground had near-perfect preservation, with less than 5% of its carbon lost due to decay over millennia (Zeng et al., 2024). Other assessments by the Intergovernmental Panel on Climate Change (IPCC) suggest wood biomass burial could retain 99.9% of stored CO₂‑eq over a century (Gooding, 2023). Despite this, bio-blocks are not yet a mature carbon storage strategy. They have little real-world validation beyond concept, operating guidance, and early implementation (Crotty et al., 2026; Zeng et al., 2023). Currently, only a handful of companies use proprietary “bio-block” or “carbon-stiffened brick” methods to sequester atmospheric carbon (Scafidi & Denvir, 2026). 

Why are we excited?

Bio-blocks, and related biomass burial, are an inexpensive form of durable carbon storage that could be scaled up toward globally meaningful sequestration of atmospheric CO₂ (>0.1 Gt CO₂ /yr). According to one study, terrestrial photosynthesis removes six times more CO₂ each year than fossil-fuel burning emits (Zeng et al., 2024). Since most of that carbon would return to the atmosphere through biomass decomposition, storing some long term in designated sites is a major opportunity. A study in the United States estimated that about 415 Mt CO₂‑eq/yr is available for wood harvesting and storage from coarse woody debris (Hausmann et al., 2024). Broader wood-vaulting studies project gigaton-scale climate impacts, with wood burial having a theoretical ceiling of 37 ± 18 Gt CO₂‑eq/yr, a level far above any sustainable deployment, supported by an estimated ~238 Gt CO₂‑eq contained in coarse woody debris currently accumulated on forest floors worldwide (Zeng, 2008; Zeng & Hausmann, 2022; Zeng et al., 2024). Furthermore, drying and compacting biomass into bio-blocks is mechanically and practically straightforward with existing technologies. Cost is favorable for wood burial including bio-blocks, ranging between US$10–50/tCO₂ stored in most studies to as high as US$100/tCO₂ (Allen, 2025; Johnson et al., 2025; Zeng & Hausmann, 2022), but this is based on estimates rather than commercialized outcomes. Bio-block burial also provides simple, high verifiability.

Why are we concerned?

There are several limitations to bio-block burial as a viable climate solution, including possible concerns from large-scale deployment. Dry biomass storage systems fail if the barrier is breached and internal humidity rises enough to restart microbial activity and anoxic digestion of biomass, forming and leaking methane (Crotty et al., 2026; Johnson et al., 2025). This reversibility concern is highest for feedstocks with larger degradable fractions, such as agricultural residues, and lower for coarse woody debris (Crotty et al., 2026; Ximenes et al., 2019). Therefore, the durability of this type of carbon storage depends on sealing requirements, site selection, and gas monitoring (Zeng et al., 2023). 

Burying plant matter from forest floors can lead to forest nutrient depletion, habitat removal, and biomass diversion from better climate uses (Burns, 2025). Permanence concerns include uncertain long-term barrier integrity (Crotty et al., 2026), the need for decades’ worth of monitoring to ensure stored carbon doesn’t leak (Crotty et al., 2026; Zeng et al., 2023), and potential soil-carbon release from excavating deep burial pits (Johnson et al., 2025; Zeng et al., 2023). For bio-blocks to sustainably store carbon, the feedstocks are ideally sourced from low-conflict waste streams in limited amounts, protect soil health, and are evaluated for land use changes, according to the World Resources Institute (Denvir & Leslie-Bole, 2025).