Agriculture Reference
In-Depth Information
2014). Increased temperatures result in higher rates of soil water evaporation and
crop transpiration, which could lead to an increase in soil water deficits (Hatfield
et al. 2011). If climate change leads to longer periods of warmer and drier weather,
producing high yields without irrigation will be increasingly challenging. While
increased levels of CO
2
improve water-use efficiency for some plants (Hatfield
et al. 2008), the benefit will be tempered by heat-related stresses that increase water
demand (NRC 2010c). Moreover, NCR aquifers that provide irrigation water are
already under stress because of unsustainable withdrawal rates (Kromm and White
1992) and are increasingly showing contamination by nitrate and pesticides. The
IPCC projects an overall net negative impact of climate change on freshwater eco-
systems (IPCC 2014a).
Recent studies have suggested that the effect of future warming on grain crops
may be worse than previously recognized (Hatfield et al. 2011). For example,
Kurcharik and Serbin (2008) found that for each degree of future warming, with no
change in precipitation, corn yields could decrease by 13% and soybean by 16%.
The authors note that while warmer and drier conditions during spring planting
and fall harvest could help boost yields in some NCR states, higher summer tem-
peratures will likely temper yield benefits. Likewise, Schlenker and Roberts (2009)
estimated decreases in U.S. crop yields for corn, soybean, and cotton ranging from
30 to 46% by the end of the century under a slow warming scenario and 63 to 82%
under a rapid warming scenario. By mid-century under conditions of increased tem-
peratures and precipitation extremes, U.S. crop yields and farm profits are expected
to decline while annual variation in crop production increases (Hatfield et al. 2014).
Agriculture will be affected both by changes in absolute values of temperature
and precipitation and by increased climatic variation (Hatfield et al. 2011, 2014),
and adaptive measures will be needed. Adaptation is not new to agriculture, and
the analyses presented in this chapter highlight the extent to which agriculture has
already adapted to trends and variability in temperature and precipitation. The chal-
lenge for the future is to adapt to more rapid and extreme climatic changes in the
face of other environmental and social pressures and stresses (Easterling 2011,
Hatfield et al. 2014), including increasing demands for agriculture to provide bio-
mass for ethanol production (Robertson et al. 2008). Adaptive measures for agricul-
ture include (1) relying on natural resources and inputs (e.g., water, energy, land);
(2) technological innovation (e.g., breeding and genetic modification, water and
soil conservation, pest management); (3) human ingenuity (e.g., relocating crop and
animal production areas, improved agronomic practices); and (4) information and
knowledge (e.g., environmental monitoring systems, risk management) (Easterling
2011). Although these measures have been effective in increasing crop yields to
their current levels, it is not clear if further adaptation of agronomic practices and
technologies—alone or in combination—will meet the challenge (Easterling 2011).
Uncertainties in climate projections for the NCR, coupled with varying climate
trends at local levels (e.g., Kucharik and Serbin 2008), make adapting and plan-
ning for the future difficult. Agronomists are given the challenge of making crop-
ping systems more resilient to climatic change (Hatfield et al. 2011) and using an
ecosystem approach to agriculture (Robertson and Hamilton 2015, Chapter 1 in
this volume) may help. Strategies such as cover and companion crop integration
