Geoscience Reference
In-Depth Information
in the face of gradual trends, are beyond the scope of the
traditional plant physiology community. Into mid-cen-
tury, the growth rates in aggregate crop productivity will
continue to be mainly driven by technological and agro-
nomic improvements, just as they have for the past cen-
tury. Even in the most pessimistic scenarios, it is highly
unlikely that climate change would result in a net decline
in global yields. Instead, the relevant question at the
global scale is how much of a headwind climate change
could contribute in the perpetual race to keep productiv-
ity growing as fast as demand? Overall, the net effect of
climate change and CO
2
on the global average supply of
calories is likely to be fairly close to zero over the next
few decades, but it could be as large as 20-30% of overall
yield trends. Of course, this global picture hides many
changes at smaller scales that could be of great relevance
to food security, even if global production is maintained.
2.1
Introduction
Climate change is a long-term shift in the statistics of the
weather (including its averages). For example, it could show
up as a change in climate normals (expected average val-
ues for temperature and precipitation) for a given place and
time of year, from one decade to the next (Hansen 2002). We
know that the global climate is changing. The last decade of
the twentieth century and the beginning of the twenty-first
century has been the warmest period in the entire global
instrumental temperature record, which began in the mid-
nineteenth century.
Global climate
change
1. Global mean temperatures have increased by 0.74°C in
the last 100 years (Rathore et al. 2003).
2. Greenhouse gases (GHG) (CO
2
, methane, nitrous oxide)
increases are mainly caused by fossil fuel use and a
change in land usage (Figure 2.1).
3. Temperatures will increase by 1.8-6.4°C by 2100 ad.
Greater increase in rabi
.
4. Precipitation is likely to increase in kharif.
5. Snow cover is projected to contract.
6. More frequent hot extremes, heavy precipitations.
7. Sea level rises to be 0.18-0.59 m (Figure 2.2).
