Greenhouse Canada

Efficienciesin the U.K.: Growers working to minimize impact of new Climate Change Levy

June 28, 2008  By Dr. Ken Cockshull

It is a sign of the times that the
2007 British Tomato Conference was mainly concerned with how growers
could minimize the amount of carbon dioxide (CO2) given off when
growing a glasshouse tomato crop.

Dr. Ken Cockshull of Warwick HRI

It is a sign of the times that the 2007 British Tomato Conference was mainly concerned with how growers could minimize the amount of carbon dioxide (CO2) given off when growing a glasshouse tomato crop. What a contrast to 10 years ago when the debate was about how much CO2 to put into a glasshouse.
So, with the emphasis of the day on improving the efficiency of energy use, Steve Adams of Warwick HRI set the tone by showing that considerable advances had already been made. The British tomato grower of today can produce a tonne of tomatoes using less than half the energy used 30 years ago. Furthermore, Adams estimated that the direct energy cost of producing tomatoes in glasshouses today was less than six per cent of the total used directly in the whole of agriculture. Furthermore, the amount used directly in agriculture accounted for less than one per cent of the U.K.’s total carbon emissions.

In Britain, all fossil fuels used by industry are taxed through a Climate Change Levy. However, the Climate Change Agreement allows energy-intensive businesses to receive an 80 per cent discount if they can meet appropriate energy-efficiency or carbon-saving targets. Growers of glasshouse tomatoes are eligible for the discount if their energy use in 2008 will be eight per cent less than in 2003-04, the program’s reference year.


Energy the main focus for U.K. growers

Adams suggested that yet more energy could be saved, without sacrificing productivity, if greater use was made of technological advances that had already been proved to be successful. For example, growers could make more use of flexible temperature control settings that tap a tomato crop’s ability to integrate temperature. They could also make more use of thermal screens, industrial waste heat, waste incineration, and co-generation by combined heat and power units, as well as by making more use of renewable energy.

Tim Pratt of FEC Services in the U.K. expanded upon this general theme. He argued that although the Dutch “closed greenhouse” was unlikely to be adopted in Britain, because of our lack of suitable aquifers to act as heat stores, the “semi-closed greenhouse” showed promise. This is a system that draws in cool air from outside by means of fans, and then distributes it through the crop via ducts. While Pratt agreed that waste heat has the potential to save energy in glasshouse crop production, he emphasized that the glasshouse must be sited close to the source of waste heat for maximum efficiency. He argued that the U.K. urgently needed a register of organizations with waste heat to spare so that they could be matched to potential users.


Pratt also discussed obtaining energy from renewable sources, such as biomass. Unfortunately, the benefits from burning biomass had proved to be less than anticipated. One reason for this was that growers were unsure whether any of the products of combustion would be harmful to plants and so were reluctant to use the exhaust gases as a source of CO2. One solution may be to use a biomass boiler to provide the base heat-load while using a natural gas-fired boiler to provide top-up heating, when required. Pratt claimed that
it was possible to reduce a nursery’s carbon footprint by 42 per cent by installing one 500kW biomass boiler for each hectare of glass together with a small natural gas boiler supplying both CO2 and top-up heating.

The anaerobic digestion of tomato waste provides another avenue that could save energy. Philip Pearson, an English grower, described his company’s plan to use anaerobic digestion to convert tomato waste into “biogas,” a mixture largely of methane and CO2. The methane would be burned to generate both electricity and heat, and this would reduce his company’s greenhouse gas emissions. The system would also dramatically reduce the amount of plant material to be disposed of in landfill sites. Pearson’s company had to overcome many hurdles, but they now had an anaerobic digestion plant under construction.


Bronwen Jones of the U.K.’s Department of Food and Rural Affairs indicated that, across the European Union, the British government assesses that food accounts for between 20 and 30 per cent of the total climate change impacts. Livestock make the biggest single impact because they produce “greenhouse gases” that are more active than CO2.

This view was supported by Gareth Edwards-Jones, of Bangor University, who thought we should be estimating the “global warming potential” of any activity, a term that would also take account of the contributions of other greenhouse gases, such as the methane and nitrous oxide produced by livestock.

“Food miles” always feature highly in media stories of global warming but, according to Jones, the British government considers them a poor indicator of environmental impact. Discussion of food miles seems to lead inevitably to the proposal that customers should accept foods only in Britain’s “natural season.” However, Jones argued that it was politically unacceptable to ban the sale of out-of-season produce. While it was true that the environmental impact of air freight was increased because the carbon was released high in the atmosphere, these emissions represented less than one per cent of the U.K. total. She also stressed that the government could not ignore that Britain was a valuable market for many producers in Africa.  


Two other approaches frequently presented as solutions to global warming are “local sourcing” and “organic production.” In her opinion, neither approach would provide a solution under British conditions. The reasons included the
conclusion that more land would have to be cultivated as the yields from
organic systems were generally lower than from “conventional” ones. Furthermore, the soil itself is a large CO2 reservoir, some of which can readily be released by cultivation.

Future government policy will probably put more emphasis on the carbon cost of whole food chains, and on the real environmental cost of imported food. Jones explained that the overall aim of the British government is to reduce the global impacts of British food consumption and production. This approach was strongly supported by Gareth Edwards-Jones who favoured “life cycle assessments,” in which the global warming potentials of all the inputs and outputs of a process were calculated regardless of where they were created in the world.

Although Britain was concentrating on reducing energy use, the Dutch government was attempting to reduce carbon emissions directly by using a carbon trading scheme. This opinion was put forward by Hans Warmenhoven, a Dutch consultant, who believed the plan had many advantages for horticultural businesses.


The Dutch government has proposed the horticultural industry’s CO2 emissions be capped at 6.5 million tonnes/year between 2008 and 2012. Individual growers were now required to keep records of their carbon emissions and report them to a central body. This body then assessed them against an industry standard and issued either an invoice or a credit. The central body was also responsible for trading carbon credits with other industries. The eventual goal was to link the Dutch scheme to the European Union Emissions Trading Scheme.

By the end of the conference, most growers reckoned they knew why they should reduce CO2 emissions and most went away feeling they had a clearer idea of how they may do it.

Dr. Ken Cockshull is an Associate Fellow at Warwick HRI, part of the University of Warwick in the U.K

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