We estimate the impact
on greenhouse gas emissions (GHGE) of shifting
from the current average United States diet to four alternative diets
that meet the 2010 Dietary Guidelines for Americans (DGA). In contrast
to prior studies, which rely on process-based life-cycle-analysis
GHGE estimates from the literature for particular food items, we combine
a diet model, an environmentally extended input–output model
of energy use in the U.S. food system, and a biophysical model of
land use for crops and livestock to estimate food system GHGE from
the combustion of fossil fuels and from biogenic sources, including
enteric fermentation, manure management, and soil management. We find
that an omnivore diet that meets the DGA while constraining cost leaves
food system GHGE essentially unchanged relative to the current baseline
diet (985 000 000 tons of CO2 eq or 3191
kilograms of CO2 eq per capita per year), while a DGA-compliant
vegetarian and a DGA-compliant omnivore diet that minimizes energy
consumption in the food system reduce GHGE by 32% and 22%, respectively.
These emission reductions were achieved mainly through quantity and
composition changes in the meat, poultry, fish; dairy; and caloric
sweeteners categories. Shifting from current to healthy diets as defined
by the DGA does not necessarily reduce GHGE in the U.S. food system,
although there are diets, including two presented here and by inference
many others, which can achieve a reduction in GHGE.
This study implements and tests a mathematical programming model to estimate interregional, interindustry transaction flows in a national system of economic regions based on an interregional accounting framework and initial information of interregional shipments. A national input-output (IO) table, regional data on gross output, value-added, exports, imports, and final demand at sector level are used as inputs to generate an interregional IO account that reconciles regional economic statistics and interregional transaction data. The model is tested using data from a multiregional global IO database and shows remarkable capacity to discover true interregional trade patterns from highly distorted initial estimates.
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