  Increasing demand for computing has lead to the development of large-scale,
highly optimized data centers, which represent large loads in the electric
power network. Many major computing and internet companies operate multiple
data centers spread geographically across the world. Thus, these companies have
a unique ability to shift computing load, and thus electric load,
geographically. This paper provides a "bottom-up" load shifting model which
uses data centers' geographic load flexibility to lower CO$_2$ emissions. This
model utilizes information about the locational marginal CO$_2$ footprint of
the electricity at individual nodes, but does not require direct collaboration
with the system operator. We demonstrate how to calculate marginal carbon
emissions, and assess the efficacy of our approach compared to a setting where
the data centers bid their flexibility into a centralized market. We find that
data center load shifting can achieve substantial reductions in CO$_2$
emissions even with modest load shifting.
