How much biomass is produced each year and how much can we sustainably harvest?

Summary - In the first part of this series, we find that the annual global production of land-based biomass is 50 billion tons, of which roughly 8 billion tons of biomass can be sustainably harvested each year. This is determined by dividing biomass into four distinct groups suitable for energy production: wood, agriculture, food waste and manure. For each group, the amount of annual ‘production’ and the amount suitable for sustainable ‘harvest’ is determined, adhering to the ‘food, feed, fiber first’ principle.

Biomass is a hot potato at the moment.

Advocates for biomass argue that it reduces carbon emissions to the atmosphere while opponents argue exactly the opposite. Recently, this resulted in a situation in the Netherlands that projects in biomass combustion plants were cancelled or delayed. Contractors building these plants feel they have been played as subsidies are being withdrawn. Approximately 8 billion euros of subsidies are at stake.

Considering the fact that approximately 60% of all ‘renewable’ energy in the Netherlands is derived from biomass, it will become very hard for the Netherlands to achieve their climate ambitions without it. This whole debate triggered a question in me. Something it seems nobody else was wondering:

Is there enough biomass to fuel the world in the first place?

Most people do not stop to think how much biomass we actually have or need. When I asked the question whether we have enough biomass to begin with, most people just shrug their shoulders and said “no way”. Nobody believes that there is enough biomass to fuel the world. I mean, how can some trees power industrialized nations? Then again, I have never seen a proper reasoning or motivation behind this argument. Everybody just shirks it off as “impossible” without providing a calculation. I therefore decided to take a crack at it myself.

For this blog series, I will determine how much biomass exists, how much energy we use and how biomass can play a role in powering the world.

In this first part of a three part series, we will start by looking into biomass; what is it, what can it be used for and how much naturally ‘grows back’ over time. In the second part, we will have a look into our daily energy needs, focusing in particular on the different energy streams that biomass could replace. In the third part I will elaborate on my view of which energy streams can become partly or fully transitioned to biomass, along with some current day examples of industries currently transitioning to biomass.

For those of you eager to start the debate without time to read, feel free to comment below. And please let me know if you have more accurate numbers than I have used in this blog. I have to admit that when it comes to the sheer abundance of differences, facts and opinions on biomass it is sometimes hard to see the wood for the trees.

All you need to know about biomass

What is ‘biomass’ and is biomass renewable?

Biomass is organic material that comes from plants and animals. It is basically just a bunch of carbon, hydrogen and oxygen atoms bunched together in all different kinds of molecules. Biomass contains stored energy from the sun, which is absorbed by means of photosynthesis. In fact, all energy that we use on Earth - except nuclear - is derived from the Sun. You could argue that the Sun is our very own nuclear fusion reactor in the sky that provides us with free, unlimited energy. Biomass can be thus be considered a natural battery that, given the right conditions, replenishes itself. If you look at it that way, biomass seems - to me - a quite useful source of renewable energy.

Biomass can be burned directly, or converted to liquid biofuels or biogas first. When biomass is burned, the chemical energy in biomass is released as heat. Just like with fossil fuels, which are essentially ancient biomass sources from millions of years ago.

Biomass can be used for all kinds of purposes in many different energy streams. In other words, there are “all kinds of biomasses” with “all kinds of purposes”. That is not a very helpful distinction and leads to much misconception. A distinction between different types of biomass is needed in this discussion.

What kind of biomass types are there?

Due to the shear abundance of biomass types, I have categorized them into four different groups. Each group has distinct characteristics, replenish with a certain amount a year and has a specific energy content. These properties are elaborated upon in the subsequent sections, and are required in order to properly compare them with our energy needs. Once we know all there is to know about biomass and we know our daily energy needs, we can determine if there is enough biomass in the first place and how biomass best serves our energy needs.

How much biomass is produced each year and how much can we sustainably harvest?

According to Wikipedia, the estimated biomass production in the world is approximately 100 billion metric tons per year, about half of which is in the ocean and half on land. Despite the enormous potential of marine biomass to provide energy, we will only look into land-based biomass as this is more practical to harvest. That leaves us with a theoretical maximum of 50 billion tons of biomass that is produced every year. It should be noted that there is about 1,000 times more plant biomass on land than animal biomass, which basically means that we can neglect animal biomass in our assumptions.

Most of us recognize the fact that it might not be smart to harvest all the biomass that grows annually on Earth, not just for biodiversity reasons but also just practical reasons. Additionally, a significant part of this 50 billion tons of production consists of biomass dedicated to food production, used for livestock feed or used as important material purposes such as clothes. This is referred to often as the ‘food, feed, fiber first’ principle, which is the idea that these types of applications of biomass are favored over the use of biomass for energy purposes.

To get a better understanding of the numbers, the yearly biomass production for each category of biomass is determined as well as an estimate made of the total amount that can be harvested sustainably and directed towards energy purposes.

Wood and wood processing wastes - 33 billion tons production, 1.3 billion tons harvestable

The Food and Agriculture Organization of the UN, also known as the FAO, is your go-to-guide when it comes to biomass-related questions. They know pretty much everything when it comes to, well, food and agriculture. In addition they have extensive knowledge on (sustainable) forestry as well.

According to the FAO, forests cover 31 percent of the global land area but are not equally distributed around the globe. About 51 percent of global forests are available for wood supply. That is because some 12 percent of forests are in legally protected areas, while the remaining 37 percent are physically inaccessible or otherwise uneconomic for wood supply. Furthermore, the division of tropical and non-tropical forests around the world is roughly 50/50. That leaves us with a grand total of 1975 million hectares of forests, or roughly 1000 million hectares of tropical and 1000 million hectares of non-tropical forests.

Wikipedia shows that the amount of annual biomass production for tropical rainforests is roughly 2 kilograms of carbon per square meter per year. For temperate forests, this is approximately 1.25 kilograms of carbon per square meter per year. Assuming these numbers are correct (I might have misinterpreted the numbers, please correct me if you know better) we have a yearly global production of wood that is roughly 33 billion tons.

The only question that remains now is how much can we sustainably harvest from these forests? This is an incredibly hard question to answer as it is very much dependent on type of forest, management, region etc. It might be better to dedicate a separate blog on this topic altogether. I have guesstimated the answer nonetheless by looking into the amount of wood that is currently harvested worldwide.

According to the Nova-Institute, the total amount of harvested wood is about 2.73 billion tons per year. About half is used in construction, the other half is used for energy purposes. We can assume a small part of it is used for long-term purposes, such as construction in houses, but the majority of construction material can be used for energy purposes when the time arises. We can therefore conclude that roughly 1.3 billion tons of wood is harvested annually for energy purposes, which seems a reasonable estimate.

Agricultural crops and waste materials - 14 billion tons production, 1.8 billion tons harvestable

According to the NOVA institute, we harvest about 14 billion tons of agricultural goods per year. Most of it is used as feed for other animals to grow (about 6 billion) or is used for the grazing of animals (about 4 billion). Only 3% of this total is dedicated to energy crops, which are used mainly as biofuel (0.42 billion). About 23% is used as food for humans, approximately 3.2 billion tons per year.

Considering we adhere to the food, feed, fiber first principle, the amount of agricultural goods we can actually harvest for energy purposes is limited. Lucky for us however, many parts of harvested crops are not used at all.

In the case of maize for example, only 20% of what is grown is consumed as food or feed. Up to 80% of the crop, the husks and stalks, are not used and are considered waste. Other examples of agricultural crops that produce a lot of waste include sugarcane bagasse, drops and culls from fruits and vegetables, pruning etc.. It is estimated that about 998 million tons of agricultural waste is produced yearly, which is about 10% of everything that we grow (excluding grazing). When we add 3% of renewable biomass for energy use (420 million tons), we arrive at a number of approximately 1.8 billion tons per year that can be harvested for energy purposes.

Food, yard, and wood waste in garbage - 1.6 billion tons harvest

Now that we have determined that 3.2 billion tons of food is produced each year, we need to know how much is left after it has been ‘consumed’. We know that, sadly, a large part of the food we produced becomes waste.

In general, we are faced with an incredible percentage of food that is simply wasted due to non-consumption of various reasons. These range from bad weather, processing problems, overproduction and unstable markets, overbuying, poor planning or simply confusion over labels and safety. Between 33-50% of all food produced globally is never eaten. For the U.S. this percentage is about 40%. On top of that, some of the food that we eat is still usable for other purposes afterwards, such as cooking and frying oil.

In developed areas with proper infrastructure, the waste is collected and turned into proper compost and biogas, such as in some places in the Netherlands. In such cases it is already made to good use. Areas that lack this infrastructure turn it into compost or might simply see it go to waste.

Without looking into the practical issues of collecting the waste and setting up these supply chains, I assume that 50% of food, yard and wood waste can be made available for energy purposes, roughly 1.6 billion tons.

Animal manure and human sewage - 3.38 billion tons harvest

Now that both food and food-waste have been used and digested, we can have a look into what is left at the bottom end. Though this might not be the most sexy and appealing form of biomass, it is still an incredible source of energy.

To determine the total ‘production’ and thus harvestable amount of animal manure, we need to define which animals we take into account first. According to the Dutch Center for Statistics (CBS), roughly 80% of all manure in agriculture is produced by cows. Therefore, to make our estimate simpler and slightly on the conservative side, we will look into cows only. Next we need to know the amount of manure cows produce, and the total amount of cows in the world. In an article of the Journal of Carbon Research, it can be found that feedlot cattle can generate a daily amount of manure equal to 5–8% of their body weight. This results in a dry mass per animal of about 5.5 to 7.3 kg per day. According to the FAO, the world has 1.468 billion cows running around, about 1 cow per family. Multiplying the amount of cows with the lower end of manure they can generate, we end up with 2.94 billion tons of manure each year.

For humans we take the same approach: we simply estimate the amount of poop we produce per day and multiply this with the number of people in the world. This has already been done by Franklin Huang from Stanford. According to his calculations, humans produce a total of 0.44 billion tons per year, resulting in a combined yearly total of at least 3.38 billion tons of animal manure and human sewage.

How much energy does biomass contain?

Naturally the energy content depends heavily on all kinds of factors such as wood type, soil type, region of the world, how the biomass has been handled, the age, you name it. Instead of stating it is too difficult and being bogged down by the specifics, I will provide a low and high estimate of the energy content for each type of biomass.

Both Wikipedia and Energies state that the energy content of ‘woody’ and plant-based biomass is between 4.1-5.6 kWh per kilogram. For sewage and manure, animal-based biomass, the energy content is roughly 3.5 kWh per kilogram according to Franklin Huang from Stanford. This makes sense, as we consumed the energy from the plant-based and animal biomass.

Although the assessment of a biomass source should not be based solely on the energy content, but also on the ease of transport, treatment, storage, and safety of its use, biomass production combined with its energy content provides an estimation of the daily available energy from biomass.

End Result

How much biomass is produced each year and how much can we sustainably harvest?

Each year, 50 billion tons of land-based biomass is produced ‘naturally’ by the world, of which 99.9% is plant-based. About 16.7 billion tons of this is used for human purposes: food production, feed and grazing for livestock, and finally for specialized crops and wood to be used for energy and material purposes. Almost half of this production - or what remains off it after it has been used - can be harvested directly and sustainably. This results in a whopping 8.1 billion tons of biomass which can be sustainably harvested each year, as can be seen below.

Harvesting this amount of biomass in a sustainable manner poses some serious logistical and operational challenges however.

We cannot harvest all the biomass in the world, right?

Hypothetically I believe we could, but I also think we shouldn’t. Next to basically destroying our eco-system, this would create severe logistical and operational issues, not to mention the fact that that the entire supply chain to harvest all the biomass in the world needs to set up. A good example of the difficulty of harvesting biomass can be shown in the case of manure and human sewage, which we have identified as the largest source of sustainable biomass.

Assuming a proper sewage system, virtually all human excrement can be collected. For much of the Northwestern hemisphere, the percentage of people connected to a sewage system is well above 90%. For many other countries however, the number is closer to 50%, not registered at all or simply non-existent. For animal manure it is even more difficult, as in most cases it is stored in open ponds (called lagoons) or pits and is untreated as fertilizer to farm fields. Usually however, the amount of fertilizer greatly exceeds what the land is capable of absorbing.

“Harvesting” of biomass for energy purposes is thus challenging and easier said than done. Nonetheless, the fact remains that there is still a tremendous amount of biomass potential remaining untapped in the form of untouched woody biomass and better use of agricultural resources.

What potential for biomass is there?

One could argue that the amount of readily available biomass can easily be doubled if we could make use of the 5.9 billion tons of animal feed. You are reading this correctly. If we went full vegan starting next January (new year new us), we could harvest the animal feedstock and use it purely for energy purposes. Though this would be the ideal scenario for some as more people are adopting a meat-less lifestyle, it is still quite unlikely to happen. In countries like China for example, more and more people are eating meat due to rising income.

Another untapped potential in my opinion is to simply increase the amount of woody biomass for energy purposes. Despite the current debate surrounding this source of energy, I find myself wondering. Is it really worse than pumping up ancient forest and dinosaur remains (also biomass) in the form of fossil fuels? Since when did sustainable forestry become worse than using coal or other fossil fuels? In my opinion, we should be using a lot more woody biomass from our forests as long as it is done in a sustainable manner and biodiversity as well as human rights are respected.

Finally, it should not have gone unnoticed that I have not even discussed the potential for water-based biomass. Why is that? It is not just because water-based biomass consists mostly of animals and poses even greater logistical challenges in terms of harvest. Despite the fact that science (and science-fiction) has been writing and researching the use of algae as miracle food- and feedstock for decades, it has not yet come to pass. Even though algae farming is backed by the fossils such as Exxon, economic viability remains to be seen.

How can we fuel the world using biomass?

We can now conclude the potential of biomass is vast. When we consider biomass to be naturally occurring batteries fueled by our very own nuclear fusion reactor in the sky (the Sun), using biomass for energy purposes can be considered perfectly sustainable if we adhere to the ‘food, feed, fiber first’ principle and respect human rights and biodiversity.

In the next two parts of this blog, I will show how much energy we actually need and where we need it, as well as showing how we can redirect sustainable biomass use to fuel the world of tomorrow.

Personal Note

The more you learn, the more you realize what you do not know. The available literature is abundant and confusing, and I believe this blog will become more of a ‘living blog’ that needs improvements over time as I learn more about biomass. I have to admit that I am pretty sure that I made a few mistakes (especially in the wood production part) and I believe that is ok.

We should not be afraid of making mistakes in this debate just because some people politicize it for their own gains. We should focus on understanding each other, look at the underlying physical truths and aim for creating a better world for tomorrow.

My basic belief is that in principle, biomass is in the very least more sustainable than fossil fuels as long as we adhere to the ‘food, feed, fiber’ first principle and not infringe on human rights or biodiversity. It is exactly these requirements that make the debate so politicized. The prerequisites for sustainable biomass use might be so stringent that in the future, we would better look at alternatives such as synthetic-solar, algae or seaweed production. Or perhaps we could use agricultural land that becomes available after the 3D printed meat revolution. These are all brilliant options but do not solve our issues now. We should not underestimate the abundance of biomass which can be sustainably harvested if we put our minds to it.

I am relentless. I will continue exploring options to reduce climate impact that are valid in my own line of work, including the use of biomass. I believe we must all do the same.

References & Further Reading

Financieel Dagblad - Bouwers van biomassacentrales zien markt instorten

Financieel Dagblad - Coalitie wil snel einde aan subsidies op verbranding biomassa

ABN Amro - Bomen over biomassa

U.S. Energy Information Administration - Biomass explained

Wikipedia - Biomass

Energy.Gov - Bioenergy frequently asked questions

Bio-Based.EU - Biomass graphics

National Geographic - Biomass Energy

FAO - Towards Sustainable Forestry

FAO - State of the World’s Forest

Dutch Government (PBL) - Beschikbaarheid en Toepassingsmogelijkheden van Duurzame Biomassa

Energies - Biomass potential from agricultural waste for energetic utilization in Greece

Nigerian Journal of Technology - Agricultural Waste Concept, Generation, Utilization and Management

Foodprint - The problem of food waste

Stanford - Biomass Energy: Poop by Franklin Huang