Agriculture Reference
In-Depth Information
Fig. 4.3
Global temperature, 1800-2006 (globalissues.org)
by the end of the twenty-fi rst century, depending
upon the adoption of developmental pathways
by countries. Increasing temperatures and car-
bon dioxide levels in the atmosphere along with
the uncertainties in annual precipitations will
have adverse effects on agriculture. Biomass and
yield tend to decline with increasing tempera-
ture, as higher temperatures shorten crop dura-
tion, enhance respiration, and reduce time for
radiation interception (Rawson et al. 1995 ). As
yields in some of the most productive regions of
the world are approaching a plateau or even
declining (Pathak et al. 2003 ), the likely effect of
climate change on crop production adds to the
already complex problem. It is a major challenge
to evaluate the impact of rising temperature on
crop yield.
In the 1880-1935 period, the temperature
anomaly was consistently negative. In contrast,
since 1980 the anomaly has been consistently pos-
itive. The 1917 temperature anomaly (−0.47 °C)
was the lowest year on record. Since 1917, global
temperature has warmed, with the most recent
years showing the highest anomalies of +0.6 °C in
the past 120 years (Fig. 4.3 and Table 4.6 ).
When the optimal range of temperature values
for a crop in a particular region is exceeded, crops
tend to respond negatively, resulting in a drop in
yield. The optimal temperature varies for differ-
ent crops. Temperatures greater than 36 °C cause
corn pollen to lose viability, while temperatures
higher than 20 °C depress tuber initiation and
bulking in potato.
Table 4.6 Global top 10 warmest years (Jan-Dec)
Global top 10 warmest
years (Jan-Dec) Anomaly °C Anomaly °F
2010 0.62 1.12
2005 0.62 1.12
1998 0.60 1.08
2003 0.58 1.04
2002 0.58 1.04
2009 0.56 1.01
2006 0.56 1.01
2007 0.55 0.99
2004 0.54 0.97
2001 0.52 0.94
Source: Annual State of the Climate Global Analysis,
National Climatic Data Center, NOAA, December 2010
Most agronomic crops are sensitive to episodes
of high temperature. Air temperatures between 45
and 55 °C that occur for at least 30 min directly
damage crop leaves in most environments; even
lower temperatures (35-40 °C) can be damaging
if they persist longer. Vulnerability of crops to
damage by high temperatures varies with devel-
opmental stage. Prolonged hot spells can be espe-
cially damaging (Mearns et al. 1984 ). Critical
stages for high temperature injury include seed-
ling emergence in most crops, silking and tassel-
ing in corn (Shaw 1983 ), grain fi lling in wheat
(Johnson and Kanemasu 1983 ), and fl owering in
soybeans (Mederski 1983 ). Soybean is one crop
that seems to have the ability to recover from
heat stress, perhaps because it is indeterminate
(i.e., grows continuously).
 
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