From Warming to Warning: The Environmental Impact of Greenhouses

The rise of greenhouses has been a game-changer for agriculture, but at what cost to our planet? From the steel skeletons that frame their glass walls to the energy-intensive practices within, greenhouses are not without their drawbacks.

The use of plastics in agriculture, or plasticulture, has become increasingly common, with countries like China, South Korea, Spain, and Turkey utilising vast amounts of agricultural plastic. The repercussions of this trend are profound, with concerns about toxic air pollution and microplastics accumulating in our soils and waters. 

Furthermore, greenhouses' energy and water use efficiency is under scrutiny, as they consume substantially more resources than alternative agricultural methods, raising questions about their sustainability, especially in water-scarce regions. 

Through deep research and informative insights, we will dissect the environmental costs of greenhouses, including their role in greenhouse gas emissions and the pollution associated with their construction. 

This article will address a specific problem with the widespread use of greenhouses: their significant environmental impact. We will provide an overview of how the construction and operation of greenhouses contribute to environmental degradation, focusing on the worldwide perspective of this negative impact.

The global greenhouse market was valued at approximately GBP 17.4 billion in 2020 and is projected to reach about GBP 31.7 billion by 2026. This rapid growth underscores the increasing demand for fresh produce and the role of greenhouses in meeting this demand. However, the expansion of the greenhouse industry also raises concerns about its environmental impact, particularly in terms of energy use and the materials used for greenhouse construction.

When we talk about a greenhouse, we're referring to a structure, often made of glass or plastic, designed to cultivate and protect plants by creating a controlled environment.

These structures are typically enclosed by glass or multiple layers of plastic, allowing sunlight to penetrate and warm the interior, thus creating an ideal growing environment for plants year-round. 

Greenhouses can range from small sheds to industrial-sized buildings and are used for various purposes, including growing vegetables, flowers, and exotic plants and conducting scientific research.

The global area dedicated to greenhouse vegetable production is estimated to be 496,800 hectares (1,228,000 acres). This figure includes permanent greenhouse structures but does not encompass other forms of protected agriculture, such as tunnels or row covers. In addition, it is important to note that this figure does not represent the number of individual greenhouses but the total area they cover globally.

This data highlights that Asia hosts nearly half of the world's greenhouse vegetable area, with Europe following as a significant contributor to global greenhouse vegetable production. 

Greenhouses have become a staple in modern agriculture, enabling the production of food and flowers in regions and seasons that would otherwise be inhospitable. However, their environmental impact is a topic of increasing concern. The operation of greenhouses, especially in colder climates, often requires significant energy consumption for heating, lighting, and ventilation. 

This energy is frequently sourced from fossil fuels, contributing to the emission of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). 

To further understand the environmental impact of greenhouses, let's look at some current data that highlights key aspects of their influence:

The global emission of GHGs has been on a steady rise, with significant contributions from various sectors, including electricity and heat production, industry, agriculture, forestry, and transportation. 

While greenhouses are not the most significant contributors to global GHG emissions, the energy-intensive nature of their operation, particularly in terms of heating and artificial lighting, makes them a significant concern. Innovations such as the "closed greenhouse" system offer some hope by reducing energy consumption through complete environmental control. 

Greenhouses, while innovative for agriculture, negatively impact the environment. Traditional greenhouses, often powered by non-renewable energy sources, contribute significantly to CO2 emissions. For instance, conventional greenhouses emit approximately 575kg of CO2 per ton of harvested lettuce, underscoring the environmental cost of such agricultural practices.

Advanced greenhouses, which utilise renewable energy and closed-loop water systems, fare better, emitting 352kg of CO2 per ton of harvested lettuce. This comparison highlights the potential for reducing the environmental impact of greenhouses through technological and methodological advancements.

Greenhouses require significant energy to maintain optimal growing conditions, especially in colder climates. This energy is often sourced from fossil fuels, leading to carbon emissions. 

The construction of greenhouses also has environmental implications. Materials like steel and glass are energy-intensive to produce and transport, and the construction process can lead to habitat disruption.

In addition to the above, the production and disposal of greenhouse coverings, such as plastic sheets and fibreglass, contribute to waste and plastic pollution. These materials, often non-renewable and not easily recyclable, can break down into microplastics, posing health risks to animals and humans alike.

The environmental concerns associated with greenhouses include:

This widespread use of plastics in agriculture, known as plasticulture, has raised substantial concerns about sustainability and environmental health. As much as 3 per cent of China's farmland is covered with plastic greenhouses, with significant usage in South Korea, Spain, and Turkey. Moreover, quantifying the total impact of greenhouses is complex, as it varies based on location, size, and management practices.

The environmental footprint of greenhouses extends beyond just plastic pollution. Energy consumption is a significant concern, with greenhouses requiring substantial energy for lighting, heating, and cooling. For instance, the energy needed for greenhouse lighting can account for about 30% of its operating costs. This energy use contributes to greenhouse gas emissions, especially when sourced from non-renewable energy supplies.

On a daily basis, the energy use in greenhouses varies depending on factors such as size, construction, and the specific crops being grown. For example, the energy consumption of plant growth chambers at Cornell was measured over a 24-hour under average conditions, highlighting the continuous energy demands of maintaining controlled environments.

The impact per usage of greenhouses can be mitigated by adopting energy-efficient technologies such as LED lighting, which can reduce lighting costs by approximately 60%. Moreover, greenhouses can save up to 61% water compared to outdoor farming, thanks to efficient irrigation methods and reduced evapotranspiration rates.

This table illustrates the increasing trend in greenhouse gas emissions from agricultural activities, including greenhouse farming, and its correlation with rising atmospheric CO2 levels and global temperatures.

Industries that contribute to greenhouse emissions include:

Greenhouses, by their nature, are controlled environments designed to optimise plant growth. While greenhouses are not inherently toxic, using hazardous materials and the potential for exposure to higher concentrations of chemicals pose health risks to workers. The enclosed nature of greenhouses means that workers might be exposed to higher levels of these substances than outdoor environments. 

The implications that these chemicals, intended to protect our crops, are leaching into the natural environment and surface waters are potential detriment to both wildlife and human inhabitants.

However, there are about two reported incidents per year in Great Britain where individuals have suffered ill health due to exposure to chemical pesticides in greenhouses. The primary health concerns identified include irritancy, asthma, allergic alveolitis, and dermatitis. 

As structures, greenhouses are not typically biodegradable because they are often made of materials like glass, plastic, aluminium, or steel, which are not biodegradable.

Plastics, a common component of modern greenhouses, pose a significant environmental threat. Most greenhouse plastics are not biodegradable, leading to long-term environmental pollution. When these plastics are discarded, they can take hundreds of years to decompose, releasing toxic pollutants into the soil and waterways. These plastics also emit harmful air pollutants when burned, contributing to air quality degradation.

The issue of waste management in greenhouse production also extends to organic wastes, such as plant biomass and nutrient-rich water, which, if not properly managed, can contribute to environmental degradation. 

While removing greenhouses entirely may not be feasible, reducing their environmental impact is essential, given their role in food production. This involves improving recycling efforts, repurposing materials, and adopting practices that lower greenhouse gas emissions.

A more sustainable approach may involve improving the environmental performance of greenhouses rather than eliminating them.

Recycling the components of greenhouses presents a viable solution to mitigate their environmental impact. Glass and metals can be recycled multiple times without losing their quality, reducing the need for virgin materials and the associated energy consumption and greenhouse gas emissions.

Recycling plastics from greenhouses, although more challenging due to potential contamination and the variety of plastics used, can still significantly reduce environmental impacts if done correctly.

Wood, often used in the structure of some greenhouses, can be repurposed or recycled into wood chips for landscaping or biomass for energy production, further reducing waste and emissions. 

However, the feasibility and efficiency of recycling greenhouse materials depend on local recycling facilities' capabilities and the availability of markets for recycled materials. For instance, greenhouse or sheet glass should be handled cautiously as it's not accepted in local council curbside recycling bins or household waste recycling centres.

Greenhouses have the potential to be sustainable. The sustainability of greenhouses hinges on several factors, including energy use, waste management, nutrient emissions, and the type of energy sources utilised. 

First, sustainable greenhouses present many opportunities to harmonise ecological integrity with agricultural advancement. For instance, renewable energy sources like solar panels with solar batteries or air-source heat pumps can substantially reduce the carbon footprint of heating these spaces. Such energy efficiency measures lower emissions and cut operational costs in the long run.

Additionally, integrating technologies such as semi-transparent organic photovoltaics (OPVs) on greenhouse roofs can contribute to energy generation while allowing for healthy plant growth. 

Waste management is another critical aspect of sustainable greenhouse operations. Organic waste, such as plant biomass, can be recycled into renewable energy, CO2, and fertilisers, which can then be reintroduced into the greenhouse system, minimising environmental impact.

Moreover, sustainability in greenhouses extends to intelligent water management practices. Implementing rainwater harvesting and drip irrigation is a testament to our ability to use resources more judiciously. These techniques promote water conservation, ensuring that every drop of this precious resource serves its purpose without waste.

Globally, greenhouse gas emissions from human activities have surged by 43% from 1990 to 2015, with carbon dioxide accounting for most of these emissions.

There are several alternatives to traditional greenhouses for those looking to extend their growing season or cultivate plants in controlled environments:

Vertical farming emerges as a compelling alternative, especially when powered by renewable energy. This method can drastically reduce CO2 emissions to as low as 158kg per ton of harvested lettuce, showcasing an impressive 70% reduction compared to open-field agriculture. Moreover, vertical farming significantly diminishes land and water usage, contributing to a more sustainable agricultural framework.

Whether greenhouses are better than their alternatives depends on several factors, including the specific needs of the gardener, budget constraints, available space, and environmental considerations. 

Traditional greenhouses offer a controlled environment for many plants, can be used year-round, and effectively protect plants from pests and harsh weather. However, they can be expensive to construct and maintain and may require more space than is available to some gardeners.

Household consumption is a major driver of greenhouse gas emissions. For instance, over 20% of all emissions are directly attributed to household consumption, which rises to nearly 80% when considering indirect emissions.

The operation of greenhouses, especially those in colder climates, requires significant heating, cooling, and lighting energy. For instance, supplemental lighting in greenhouses can account for about 30% of their operating costs. This energy use directly translates to carbon dioxide (CO2) emissions, the primary greenhouse gas emitted through human activities. 

To put the environmental impact of greenhouses into perspective, consider the following comparisons:

Let’s delve into the statistics, facts, and figures surrounding greenhouses, highlighting their global market and environmental impact. This is based on data sources from environmental studies: EPA, NASA, Our World In Data, and others.

The global greenhouse market was valued at approximately £19.4 billion in 2022 and is projected to grow at a compound annual growth rate (CAGR) of 9.9% from 2023 to 2030.

North America and Europe also represent significant markets with ongoing greenhouse technology and infrastructure investments.

As of 2019, the global area dedicated to greenhouse vegetable production was estimated at 496,800 hectares. 

Globally, the primary sources of greenhouse emissions are electricity and heat production (23%), industry (24%), and agriculture, forestry, and other land use (22%).

The largest greenhouse-producing areas in Europe as of 2022 were Spain (46,000 hectares), Italy (25,000 hectares), France (9,500 hectares), and Greece (3,800 hectares).

The largest group of greenhouses in the world is located in Leamington, Ontario, Canada, with about 200 acres of tomatoes grown in glass greenhouses.

Greenhouses can be made from various materials, including polyethylene (a lightweight plastic) and glass.