As the number of people consuming cannabis continues to grow, it’s important to consider the environmental impact of this industry. While cannabis has many potential benefits, it also has significant environmental consequences that must be taken into account. In this week’s newsletter,  we will explore some of the scientific facts related to cannabis and the environment, uncovering how its cultivation can have both positive and negative impacts.

Cultivation Methods and Purpose 

First of all it is important to distinguish between cultivation methods. As we already discussed in newsletter 10, cannabis can be grown indoor, outdoor or in mixed light, resulting in different yields and different environmental impacts. Closed indoor systems rely on the artificial provision of soil, nutrients, water and light. They allow higher levels of control but require high energy inputs. Outdoor cultivation on the other hand operates in a different manner, similarly to traditional crops: plants are grown in amended soil, using the sun as a energy source, and rainfall, stream diversion, springs and wells as a source of water. This system requires lower energy inputs, but uses rural resources such as land and water, and is highly permeable to environmental changes. A third option is a mixed method, usually performed in greenhouses, which allows a closed environment that requires a much lower energy input, but offers a higher level of control. Finally, a recent study by Wartenberg et al., distinguishes a fourth sub-category: the trespass system, illegal outdoor cannabis cultivation sites on public land. This unregulated system can be particularly damaging for the environment and agriculture since water is usually drawn without permission and toxic pesticides are often used, which can end up as run-off into potable water sources (1). 

It is also important to distinguish between plant types when talking about the environmental impact of cannabis. The term cannabis mainly applies when the plant is consumed for recreational or medical use, while the term hemp applies to plants with low THC levels, used for lots of different purposes (Newsletter 12). 

Negative environmental impacts

Systematic or cumulative analyses of cannabis cultivation impacts are currently lacking, but negative environmental impacts have been identified in cannabis production and should be addressed. 

Water

One of the most pressing concerns is the amount of water needed to grow cannabis. With a water requirement two times higher than maize, soybean, and wheat, during the growing season (June to October), cannabis is considered a thirsty plant (2). For comparison, it was estimated that the cannabis plant needs 22.7 L of water per day, while wine grapes in the same area, another major irrigated crop, only uses 12. L. (3,4). This water usage can put a strain on water resources, especially in areas with limited water availability or during droughts. Moreover, cannabis cultivation can reduce or alter stream flow, thus threatening wildlife. It reduces habitat availability and interferes with the life cycle of certain fish species by increasing water temperature, disease transition and physiological stress of wildlife, while decreasing food supply, food production and oxygen availability (5). 

While peer-reviewed studies quantifying the impacts of cannabis cultivation on water quality don’t exist yet, recent studies have suggested that the considerable amount of nutrients and pesticides required by the cannabis plant could deteriorate water quality, especially in unregulated “trespass systems”. In the late 2000s, the death of a male fisher was connected to acute AR (anti rodent) poisoning, most likely due to the source of numerous illegal cannabis cultivation sites, suggesting that illegal cultivation of cannabis leads to inadequate operational practices which results in water pollution and can damage wildlife (2). 

It is crucial to identify and implement effective irrigation practices to minimize the negative environmental effects on water resources.

Air pollution

When grown outdoors, excessive fertilization of cannabis can cause deterioration in air quality. Nitrogen oxides and ammonia, released by nitrogen fertilizers, can have detrimental effects on air quality and human respiratory health. They can travel long distances, contaminating ecosystems far away from the original sources, causing eutrophication and acidification of water bodies – which stimulates excessive growth of algae, leading to oxygen depletion, and aquatic biodiversity loss – while also impacting soil quality, nutrient cycling, and ecosystem dynamics (6,7). 

On the other hand, when grown indoors, high temperature and high humidity helps the growth of mold, which can cause respiratory symptoms to the growers (2). And, while the impact of pesticides and fertilizers on the environment is reduced, indoor cultivation poses a direct risk to the health of the growers, exposing them to potentially harmful compounds (8).

Finally, experimental results suggested that biogenic volatile organic compounds (BVOCs) emissions from both indoor and outdoor cultivation could contribute to ozone formation and particulate matter pollution (1,8).

Energy consumption and carbon footprint 

As one of the most energy-intensive industries in the USA, cannabis production accounts for at least 1% of the nation’s electricity, mainly due to indoor cultivation (9,10). Estimates suggest that a single indoor cannabis plant can use as much electricity as a refrigerator, with an energy demand of  6074 kWh kg-yield−1 (10). High intensity lighting is the main contributor, followed by HVAC (heating, ventilation, and air conditioning) and dehumidification (10). In this case, it is not the plant directly producing environmental pollutants, but the production of energy consumed, which, especially if generated from fossil fuels, is accountable for the environmental impact. 

Land use 

Cannabis cultivation also has implications for land use. Due to historic prohibition, cannabis is cultivated on marginal agricultural land of high ecological importance in many countries  (11). The expansion of the cannabis industry may increase soil erosion (12,13) and forest fragmentation, resulting in degradation of ecosystem functions (8). In many African countries for example, the preference for cannabis cultivation in forested areas means that sensitive watersheds with high biodiversity are degraded, leading to habitat loss for many species (11). When cannabis is grown indoors, it often requires the use of large facilities that can have a negative impact on the surrounding community. These facilities may emit noise, light, and odors that can be disruptive to nearby residents, and the disposal of waste products such as soil, plant material, and chemicals can create additional environmental problems.

Positive environmental impacts

While there are certainly concerns about the environmental impacts of cannabis cultivation, there are also potential benefits that should be considered.

Carbon sequestration 

Like every plant, cannabis absorbs carbon dioxide from the atmosphere during photosynthesis, which can help to mitigate the effects of climate change. While it is true that they produce BVOC that can damage the ozone, they also consume significant amounts of carbon dioxide compared to that taken up by trees and therefore can clean air of excessive carbon dioxide (14). Moreover, the sequestered carbon is stored in the soil as soil organic matter, which increases soil structure, stability, drainage, fertility and encourages biodiversity. 

Bioremediation and promotion of sustainable practices

Thanks to their bio-accumulative ability, cannabis plants can improve soil quality by lowering the concentration of heavy metals, which can be dangerous for other species (15). Also, it was reported that cannabis plants can improve micronutrients availability in the soil (11). 

Moreover,  there is a growing interest in regenerative practices among cannabis growers, which recognize the environmental benefits of sustainable practices and prioritize the restoration of soil health, biodiversity, and ecosystem resilience in their operations.

Hemp as a source of sustainable solutions 

In a previous newsletter (Newsletter 12) we discussed how hemp has a large variety of industrial applications, and how these bring sustainable solutions to the market. Paper production from cannabis plants is more efficient and reduces deforestation, and the paper itself can be recycled more times compared to wood pulp paper (16). Biodiesel can be made from hemp biomass, with a 97% conversion efficiency from hemp oil to biodiesel (17). Hemp is also one of the strongest and most durable organic fibers on earth, said to have three times the tensile strength of cotton (18). It just needs a third of the water needed for cotton and produces 220% more fiber (18). 

Conclusion and recommendations

It is clear that cannabis/hemp cultivation can have both positive and negative environmental impacts. In order to minimize negative environmental impacts associated with cannabis expansion, policy recommendations include promoting wildlife-conscious farming practices, incentivizing efficient water management and establishing water licensing systems, implementing pesticide controls specific to cannabis cultivation, encouraging energy-efficient practices and the use of renewable energy sources, and prioritizing science-based best practices to reduce air pollution. New sustainable agricultural practices as well as new biotechnologies (Newsletter 15) could improve cannabis/cannabinoids production and make it more sustainable. Moreover, in addition to their utilization for flower production, cannabis plants hold the potential to be harnessed for biomass purposes, enabling a closed-loop system where various parts of the plant can be utilized efficiently, in a “closed loop”. 

As the cannabis industry continues to grow, it is important to invest in research and innovation that can help to reduce the negative impacts of cannabis cultivation on the environment, and enhance the positive ones.