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Cheng et al. Carbon Footprints 2024;3:10 https://dx.doi.org/10.20517/cf.2023.53 Page 9 of 13

Figure 4. The effect of grid decarbonization on the climate performance of the plant factory. (A) Power source mix of China’s grid
decarbonization scenarios (C-coal, G-natural gas, S-solar, W-wind, N-nuclear, and H-hydro). Heat maps represent 64 decarbonization
pathways (rows) clustered into 12 high- and low-scenarios. (B) GWP of plant factory at high- and low-decarbonization levels. The
reference is the GWP baseline on China’s Southern Power Grid. (C) the corresponding TWP. TWP < 1 means the plant factory is more
beneficial to the climate than the greenhouse, and vice versa for TWP > 1, and TWP = 1 means the equivalent climatic performance. The
uncertainties were sourced from 17 CO impulse-response models [16] . The left y-axis represents the metrics of TWP CH4 and
2
TWP CH4+N2O , while the right y-axis represents the inverted U-belts reflecting the deficiency between TWP CH4 and TWP CH4+N2O .

84%-90% of the life cycle climate burden of lettuce cultivations by plant factory, contrasting with the
9%-15% share of the upstream methane emissions. For most scenarios of grid decarbonization, more than
90% of methane emissions come from the coal combustion of upstream power generations. However, in the
2050-high decarbonization scenario, the share of upstream methane emissions decreases to about 4% of the
overall climate burden. This can be attributed to the dramatic phase-out of coal-fired power generation. In
addition, grid decarbonization has less impact on nitrous oxide emissions, which share the least amount.

DISCUSSION
Given the short-lived methane emissions from upstream power generations and nitrous oxide emissions
from fertilizer uses, we developed the LCA models to quantitatively compare the GWP of lettuce grown by
plant factory and greenhouse. TWP metric was developed to dynamically compare the climate advantage of
the two vegetation cultivation systems through cumulative radiative forcing of multiple GHGs. For
greenhouse, the 100-year GWP of 1 kg lettuce is comparable with previous estimates in Italy and Spain