Quantifying the Environmental Impact of Doubling Hawaii’s Local Food Supply

Producer Surveys. We completed interviews with 20 lettuce producers (n = 14 land grown lettuce, 3 hydroponically grown lettuce, 3 produced aquaponically grown lettuce), 25 banana producers, 10 carrot producers, and 12 ranchers. Yields for all products were slightly lower than yields previously reported in Hawaii or in other subtropical environments.

Hawaii Markets. Hawaii lettuce farmers sold their produce to retailers on the islands of Oahu, Maui, Kauai, and Hawaii Island. Hawaii-produced lettuce was consumed both on the islands where it was produced, and transported between islands, to grocery stores, farmers markets, and restaurants. In contrast, carrot and banana production captured in the survey was not transported between islands, and was mainly sold at farmers’ markets (carrots and bananas), grocery stores (bananas), and restaurants (carrots). For beef, around 33% of the cattle born each year were exported to the mainland, which contrasts with about 80% of Hawaii cattle exported according to UHM CTAHR Cooperative Extension. Cattle raised and consumed in Hawaii are transported to a processing facility which may be on another island and then the final product is distributed from that facility all over the state.

Import Origins. All focal food imports are typically shipped to Hawaii via ports in California. Lettuce is usually produced domestically in California and Arizona; banana is imported from Central and South America; most carrot production occurs in California; and beef is sourced from the US mainland, Australia, or New Zealand.

Import versus Local Food Relative Impacts. Here, we compare the relative environmental impact of the food on a per kilogram, or production-scaled, basis (impact per kg production).

Land Use: Every focal Hawaii-grown food except hydroponic lettuce used more land relative to imports (i.e., Hawaii produced food had lower yields than imported foods). Although both aquaponic and hydroponic lettuce are grown vertically and require relatively little land, land is needed to produce fish feed for aquaponic lettuce, which means that total land area for this system is larger than that of hydroponic lettuce.

Climate Change: All Hawaii-grown crops except banana had a larger climate change footprint than imports. Bananas were imported to Hawaii from Central and South America, driving relatively high transportation emissions and a larger carbon footprint than Hawaii-produced bananas. Grass fed beef was associated with greater emissions than grain-fed beef, so that Hawaii-produced beef had more climate change impact than imports from the mainland US (largely grain fed), but lower impact that imports that were grass fed (New Zealand and Australia).

Emissions from the production phase accounted for majority of the gross GHG emissions for most imports and locally produced products. Exceptions were imported carrot and imported and locally produced banana. Hawaii-produced bananas sequester more carbon than they emit via transportation and other production activities, and therefore have negative net emissions. In beef, emissions are driven by enteric fermentation, feed production, and manure management rather than transport.

Freshwater Eutrophication: Hawaii grown crops tend to have higher freshwater eutrophication potential (driven by P inputs to production) than imported crops, except banana, which had slightly lower freshwater eutrophication potential. Beef of all kinds (imported and locally produced) had higher freshwater eutrophication potential than focal crops, but this impact did not differ substantially between Hawaii-produced and imported beef.

Marine Eutrophication: In contrast to freshwater eutrophication results, all Hawaii-grown crops except aquaponic lettuce had lower marine eutrophication potential (driven by N inputs to production and transport) than their imported counterparts. The aquaponic system has a higher N footprint than other crops because it requires fish feed which is produced from soy. Marine eutrophication potential from beef production was substantially higher than for crops, but differed little across imports and locally produced beef, despite differences in feed across systems.

Water Resource Depletion: All Hawaii-produced foods except beef had more water usage than imports, likely because of higher evapotranspirative demand in subtropical Hawaii compared to locations that produced imports. Yet, because Hawaii cattle are grass fed and therefore do not use water in the form of feed production, Hawaii beef used less water than US mainland beef.

Baseline Food Supply. In 2008, imports of focal crops made up majority of Hawaii’s food supply; Hawaii largely consumed imported carrot (2% of supply), banana (27%), and lettuce (2%). The same was true for beef (92%) in 2018. Thus, net environmental impact of Hawaii’s food supply is largely driven by imports under current levels of production.

Doubling Scenario. Doubling Hawaii-produced food production (relative to the baseline supply) with a commensurate reduction in imports would generate relatively small changes in impacts for most foods and impact categories because of the small change in additional local production relative to the total supply (i.e., doubling Hawaii carrot production would increase local carrot production from 2% to 4% of total supply). Because doubling banana production means that bananas would comprise 54% of total supply, meeting Hawaii’s policy goals for bananas has a higher likelihood of generating substantial change in environmental impact. Specially, our models suggest decreases in embodied climate change (-732%), marine eutrophication (-35%), and freshwater eutrophication (-3.7%), and increases in embodied land (+36%) and water use (+48%).

Discussion. Through life cycle analysis informed by producer surveys, we found that Hawaii-produced foods, which have lower yields that their imported counterparts, tend to produce higher production-scaled environmental impacts. Among foods studied, beef production generated the largest impacts, a common result in comparisons of crop and beef environmental footprints. Higher yields produced from the same amount of inputs can mitigate the environmental impacts associated with the production of the agricultural input itself (e.g. fertilizers, infrastructure). Indeed, low yields of Hawaii-produced foods likely drove their relatively higher impacts than imports across most foods and categories. Therefore, sustainable agriculture in Hawaii may depend partly on identifying, addressing, and eliminating any systemic barriers to increased yields and efficiency across the State. Our analysis also emphasizes the small role that transportation has in driving these impacts, which underscores the need to focus on management practices and production of Hawaii’s food, rather than food miles, when advocating for local food systems.

Doubling Hawaii-produced food production would generate a small absolute change in most environmental impact categories because local production currently comprises a very small fraction of total food supply. The single exception may be bananas, for which local production serves an important role in Hawaii’s food system. Though many scenarios of doubled Hawaii-production would likely produce a net decrease in environmental impacts, those environmental benefits are global (climate change) or local-distant (eutrophication) and will not directly benefit Hawaii’s environment.