The jumbo carbon footprint of a shrimp: Carbon losses from mangrove deforestation

Study Number

88

Author

J. Boone Kauffman, Virni B. Arifanti, Humberto Hernández Trejo, Maria Del Carmen Jesús García, Jennifer Norfolk, Miguel Cifuentes, Deddy Hadriyanto, Daniel Murdiyarso

Abstract

Scientists have the difficult task of clearly conveying the ecological consequences of forest and wetland loss to the public. To address this challenge, we scaled the atmospheric carbon emissions arising from mangrove deforestation down to the level of an individual consumer. This type of quantification represents the “land-use carbon footprint”, or the amount of greenhouse gases (GHGs) generated when natural ecosystems are converted to produce commodities. On the basis of measurements of ecosystem carbon stocks from 30 relatively undisturbed mangrove forests and 21 adjacent shrimp ponds or cattle pastures, we determined that mangrove conversion results in GHG emissions ranging between 1067 and 3003 megagrams of carbon dioxide equivalent (CO2e) per hectare. There is a land-use carbon footprint of 1440 kg CO2e for every kilogram of beef and 1603 kg CO2e for every kilogram of shrimp produced on lands formerly occupied by mangroves. A typical steak and shrimp cocktail dinner would burden the atmosphere with 816 kg CO2e. This is approximately the same quantity of GHGs produced by driving a fuel-efficient automobile from Los Angeles to New York City. Failure to include deforestation in life-cycle assessments greatly underestimates the GHG emissions from food production.

Main Results and Conclusions

• Mangroves are in decline across the world and especially in Southeast Asia, with the conversion to fish and shrimp ponds representing the biggest single cause of mangrove degradation in this region
  • “They (mangroves) are disappearing at the rate of approximately 1% per year, with regional estimates such as those in Southeast Asia as high as 2–8% per year” (p. 1)
• Conversion of mangroves to shrimp ponds or cattle pastures has a significant impact on the carbon stocks of that region
  • “Ecosystem C stocks of mangrove forests ranged from 269 to 1663 megagrams of carbon per hectare with a mean of 858 megagrams of carbon per hectare” (p. 3).
  •  “Within mangrove forests undergoing conversion into shrimp ponds or cattle pastures, the trees are cut and burned or physically removed from the site, often leaving only stumps or a few large pieces of dead wood (Figure 1b). As a result of this conversion process, the aboveground C stock in shrimp ponds is – on average – 91% less than that in undis­ turbed mangrove forests (Figure 2). Furthermore, there were significant losses of soil C associated with conversion. The mean belowground C pool of the shrimp ponds contained 352 megagrams of carbon per hectare, suggesting that 54% of belowground C pools (consisting of soils and roots) is lost through conversion” (p. 3).
• Mangrove deforestation is a major contributor to GHG emissions, accounting for 10% of the emissions from all deforestation globally while representing only 0.6% of the land area of tropical forests
  •  “Our measures of loss coupled with the global cover of mangroves (13.7–15.3 Mha) and deforestation rates of 1–2% yield a midpoint estimate of 0.12 Pg C yr−1 from mangrove deforestation. This is equivalent to 12% of the total emissions from all tropical deforestation (Baccini et al. 2012) and 10% from all deforestation. These carbon emissions arising from mangrove deforestation come from an area that is ≤0.6% of the land area occupied by tropical forests” (p. 3)
• Cattle pastures and shrimp ponds also emit greenhouse gases, with sizable land-use footprints
  • “Based on our calculations, every kilogram of beef produced on pastures that have replaced tropical forests has a land­use footprint of 348 kg CO2e” (p. 4)
  • “For every kilogram of shrimp produced, 1603 kg of CO2e are emitted on average. The range among our sites was 1437 kg CO2e per kilogram of shrimp produced in Honduras to 4045 kg CO2e per kilogram produced in the Dominican Republic” (p. 4)
• In terms of a single meal, two people who each ordered a meal consisting of 100 grams of shrimp and 454 grams of beef would generate 816 kg CO2e. The carbon footprint from both dinners is equivalent to the combustion of 182 gallons of gasoline from a normal car.
  • “Driving a moderately fuel­efficient automobile across the US (from Los Angeles, CA, to New York, NY) and back would have a lower carbon footprint than that of these two meals” (p. 5).