Geoscience Reference
In-Depth Information
many anecdotes, the article concludes, “Many of the failed harvests of
the past decade were a consequence of weather disasters, like fl oods in
the United States, drought in Australia and blistering heat waves in Eu-
rope and Russia. Scientists believe some, though not all, of those events
were caused or worsened by human-induced global warming.”
5
An even more somber projection was made by the prominent
Stern
Review:
“Declining crop yields are likely to leave hundreds of millions
without the ability to produce or purchase suffi cient food, particularly
in the poorest parts of the world. . . . Once temperatures increase by
3°C, 250-550 million additional people may be at risk—over half in
Africa and Western Asia.”
6
The impact of climate change on agriculture is the most carefully
studied area of impacts analysis. Do these pictures accurately refl ect
current assessments? It is worth looking at the summaries of the IPCC
Fourth Assessment Report, which provided a careful review by experts
in the fi eld.
Globally, the potential for food production is projected to increase
with increases in local average temperature over a range of 1-3°C,
but above this it is projected to decrease. Increases in the frequency
of droughts and fl oods are projected to affect local crop production
negatively, especially in subsistence sectors at low latitudes. Adapta-
tions such as altered cultivars and planting times allow low- and
mid- to high-latitude cereal yields to be maintained at or above
baseline yields for modest warming.
7
It is striking how this summary of the scientifi c evidence contrasts
with the popular rhetoric. Crop productivity or yields are the output
per acre of land under cultivation. The fi ndings here are that productiv-
ity will increase in many regions for “modest warming,” which gener-
ally means up to 3°C of local warming. The temperature projections in
Figure 9 indicate that temperature increase is expected to remain in the
modest range until the last quarter of this century.
These projections need to be qualifi ed by the uncertainties of both
climate and agricultural models. Moreover, there will clearly be losers
as well as winners. Even more worrisome is that current models do not
