Agriculture Reference
In-Depth Information
positive in the lower range of temperature rise but negative if the upper range of tem-
perature increases were to occur. While crops may benefit from the so-called CO
2
fertilization effect, yield losses may be expected if crops were to operate under high
temperature, drought, and other environmental stressors such as rising tropospheric
ozone (O
3
) concentrations. One challenge will be to develop cultivars and produc-
tion systems that are adapted to the changing climatic conditions expected to prevail
during this century and productive enough to satisfy the dietary needs of increasing
populations. There will also be other challenges and opportunities for the develop-
ment and application of agricultural technologies capable of (1) mitigating green-
house gas emissions and (2) producing bioenergy crops in a sustainable manner.
IntRoductIon
Climate
, the long-term average condition of weather and its variations over a region,
has changed significantly during the evolution of Earth. Climate has been relatively
stable during the last 10,000 years, a period known as the Holocene. Coincidentally,
or perhaps because of this climate stability, it was at the beginning of this geologic
epoch when humans learned how to domesticate wild plants and convert them into
food and fiber crops. This revolutionary change marked the beginning of the first
culture, agriculture, that allowed for the progression of human civilizations. Major
cultures emerged and developed around a relatively small number of crops such as
rice (
Oryza sativa
L.) in Asia, wheat (
Triticum aestivum
L.) in the Middle East, and
maize (
Zea mays
L.) in the Americas. Today, these crops still account for a sig-
nificant fraction of the caloric intake and nutritional diet of humans. To meet this
demand, these and other important crops have been adapted to grow under a wide
range of climatic and edaphic conditions prevailing around the world.
The development of the steam engine in Great Britain in the middle of the eigh-
teenth century started a second revolution of transformational changes that affected
agriculture, manufacturing, and transportation. These changes in turn had pro-
found effects on socioeconomic and cultural conditions worldwide. Use of coal to
power engines and expansion of agriculture grew quickly to satisfy energy and food
demands of burgeoning populations. The development of the internal combustion
engine and electrical power generation toward the end of the nineteenth century
spurred even more the need for fossil fuels and agricultural land.
Accompanying all this and as a result of these activities, however, many invis-
ible changes started to alter the chemical composition and dynamic properties of
the atmosphere. Several heat-trapping trace gases (carbon dioxide [CO
2
], methane
[CH
4
], and nitrous oxide [N
2
O]) started to accumulate beyond their normal levels as a
result of combustion of fossil fuels and conversion of land under native vegetation to
agricultural use. And gradually, scientists began to study, document, and understand
the impacts of these changes. There were very many important contributions, such as
de Saussure's demonstration of the greenhouse effect, Tyndall's experiments on the
absorption of thermal radiation by complex molecules (such as CO
2
), and Callendar's
equations linking greenhouse gases and climate change (Le Treut et al. 2007).
Two examples are given here to illustrate the evolution of our understanding of
the effect of the accumulation (or variation) of trace gases in the atmosphere. The
