Comparing fossil CO2 emissions from vegetable greenhouses in Canada with CO2 emissions from importing vegetables from the southern USA

The energy consumption and fossil CO2 emissions from the Canadian vegetable greenhouse industry were assessed using greenhouse statistics from 2002 to 2007. The fossil CO2 emissions were compared to the fossil CO2 emitted during transport of an equal weight of food by truck and by airplane from two horticultural production centers in the southern USA to four locations in Canada. The calculations in this paper for Canadian greenhouse energy use for heating were verified against farm energy use survey data collected from greenhouse operators in 1996. Allowing for extrapolations to 1996 from the 2002 to 2007 period, the survey data were underestimated by 12%. Since the survey data were not corrected for possible household energy use by greenhouse operators, some underestimation in the heat energy calculations was expected. The fossil CO2 emissions from Canadian greenhouses were 0.35 Tg. This estimate is about twice as high as the diesel fuel CO2 emissions required to truck the same weight of vegetables from south to north, but only slightly less than half the CO2 emissions to ship the same vegetables by air. Quebec greenhouse crops had the lowest CO2 emission intensity and the least difference with trucking CO2 emissions, while BC greenhouse crops had the highest CO2 emission intensity and the most difference with trucking CO2 emissions. The study revealed some potential CO2 mitigation practices including alternative fuels such as straw pellets or wood chips, non-recycle-able combustible urban waste and biogas from city waste treatment facilities or manure storage systems. Mitigation of heat energy loss could involve insulating heating lines within greenhouses and doorway designs that minimize the time and area open to the outside air. In order to reduce the CO2 emission intensity, research should aim at a higher ratio of yield to fossil energy use, rather than simply trying to maximize greenhouse yields. Crown Copyright (C) 2011 International Energy Initiative. Published by Elsevier Inc. All rights reserved.