Agriculture Reference
In-Depth Information
The reader might wonder why we haven't mentioned the
controversy of global warming itself, given the torrid rheto-
ric between global warming denialists and alarmists. Because
we are not climate scientists we will say very little about how
agricultural activities affect future temperatures. We do assert
two statements as facts, though. One is that gases like carbon
dioxide and methane are greenhouse gases that retain heat.
After all, Venus is much hotter than Mercury despite being
farther from the sun, simply because the atmosphere of Venus
contains greenhouse gases and Mercury's does not. The sec-
ond fact is that, because some activities take greenhouse gases
from the earth's crust and eject it into the atmosphere, there is
some probability that the use of fossil fuels will have a notice-
able effect on the climate within the next one hundred years.
We make no assertion as to what that probability is, only that it
is greater than zero. This chapter focuses on how food affects
emissions of greenhouse gases, not on how those emissions
affect the climate.
Throughout this chapter we will be referring to “carbon”
when we are really concerned about all greenhouse gases,
and so “carbon” really refers to carbon dioxide-equivalent
emissions—denoted CO
2
e. One ton of methane results in
twenty-one times the warming of 1 ton of carbon dioxide,
so if a ton of methane is emitted, we instead say that 21 tons
of “carbon” emissions (20 tons of CO
2
e) take place. To repeat,
when we say 1 ton of carbon, we are always referring to 1 ton
of CO
2
e.
How Does Agriculture Contribute to Greenhouse Gas Emissions?
In the 1920s, when Russian novelist Yevgeny Zamyatin wrote
his science fiction dystopia
We
, he imagined food being pro-
duced directly from petroleum. His vision was prescient.
Plants may acquire their energy from the sun, but farmers
acquire it from fossil fuels. Obviously, tractor fuel is based on
petroleum, but so is nitrogen fertilizer. Other fertilizers like
