Achieving a net zero greenhouse

What is net zero?

Net zero refers to a process whereby the amount of greenhouse gases (GHGs) removed from the atmosphere is equal to what is produced. 

Greenhouse gases

The term ‘greenhouse gas’ covers a lot of things, including carbon dioxide (CO₂), methane (CH4) and even water vapour (H₂O - although the effect of water vapour has not been officially published in the GHG Protocol, due to it rarely reaching the upper troposphere, and its complex effects and interactions with reflection and evaporative cooling). 

The main GHGs that contribute to Agricultural emissions in the UK are Nitrous Oxide (N2O) from fertiliser use and manure production, CH4 mainly from enteric fermentation of livestock, and CO2 from the use of fossil fuels and carbon changes in the soil. Agriculture is responsible for 10% of total UK emissions, 70% of total N₂O emissions, 50% of total CH₄ emissions and 1% of total CO₂ emissions. Greenhouses typically have no CH₄ and very little N₂O emissions, but have more CO₂ emissions than other farms due to lighting, heating, fans, and any attached cooled environments (packhouses etc.). 

Carbon dioxide equivalent (CO₂e) 

Importantly, not all GHGs are equal, so these are often evaluated in terms of carbon dioxide equivalent (CO2e), which considers the global warming potential (GWP) of the various emissions. Carbon neutral is another term often used to describe a net zero process. 

The relative CO₂e for those GHGs are outlined in the below table.

Fifth Assessment CO2e, defined by the GHG Protocol, for the main GHGs affecting agriculture

Achieving net zero

Reducing emissions to net zero within horticulture, as in most industries, will not be easy. There won’t be a ‘one size fits all’ solution, but rather a myriad of technologies and concepts to work with. However, bear in mind the law of diminishing returns when implementing multiple separate solutions. Each site will likely need to develop a solution bespoke to its needs, but a collaborative approach with other local sites and industries should be considered, especially where large scale infrastructure and investment is required.

In 2017, British agricultural GHG emissions made up 10% of the UK total, equivalent to 45.6 million tonnes of CO₂, with relative contributions of 5.6% methane, 3.1% nitrous oxide and 1.2% carbon dioxide. GHG emissions in horticulture are likely to differ from other sectors of agriculture and comprise mostly of CO₂ – a result of heating, lighting and direct dosing of carbon dioxide to the growing environment. While there aren’t the same opportunities for ‘big wins’ as in some other sectors, horticulture can still cut emissions through:

• increased efficiency
• renewable energy generation
• improvements in the supply chain.

For agriculture to meet its net zero targets, some sectors will have to go beyond and act as carbon sinks, to mitigate those sectors of the industry which cannot achieve zero emissions.

Technology & innovation

Find out what technological solutions and innovations you could use or implement that could help you achieve net zero in your horticultural business

Resource efficiency

The efficient use of resources, particularly energy, will be a key part of the strategy to achieve net zero. Even with significant energy generating potential on-site, it shouldn’t be wasted. Burning fuel to generate heat, electricity or carbon dioxide will have an associated cost. By only producing what you really need, emissions and costs can be reduced.

Behavioural change

The consumption of out-of-season produce and the expectation for certain crops to be available year-round are partly to blame for horticulture’s high energy usage. While horticulture is often simply supplying in response to consumer demand, perhaps we should all consider the sustainability of what we eat. Crops requiring vast quantities of heat and even supplementary light, even where the energy is produced renewably, should only be grown under a sustainable model. By opting for less energy intensive varieties and switching to more seasonal produce, the energy input can be greatly reduced.

Changing consumer behaviour is easier said than done. However, as demonstrated by the coronavirus pandemic, governments, industries and the public can adapt very quickly. The impact of lockdowns has highlighted weaknesses in the supply chain and has potentially given an insight into how life may be after our EU Exit. The ready availability of produce from Europe that society has become used to may well change, meaning a greater necessity for UK grown produce. However, what can be grown cost-effectively and efficiently, without the benefit of a Mediterranean climate, could impact consumer buying habits.

Achieving net zero: thinking inside the box

How do you know when you’ve reached net zero? Find out what site inputs and outputs you need to consider, including supply chain limits, to help you achieve net zero.

Useful information