Impacts of Climate Change on Agriculture - Climate Resilient Agriculture for Ensuring Food Security - page 78

FACE have shown that increases in CO 2 lead to
decreased concentrations of micronutrients in
crop plants (Bert et al. 1997 ). This may have
knock-on effects on other parts of ecosystems as
herbivores will need to eat more food to gain the
same amount of protein (Royal Society 2005 ).
Studies have shown that higher CO 2 levels
lead to reduced plant uptake of nitrogen (and a
smaller number showing the same for trace ele-
ments such as zinc), resulting in crops with lower
nutritional value (IPCC 2001 ; Loladze 2002 ).
This would primarily impact on populations in
poorer countries less able to compensate by eat-
ing more food, more varied diets, or possibly tak-
ing supplements.
Reduced nitrogen content in grazing plants
has also been shown to reduce animal productivity
in sheep, which depend on microbes in their gut
to digest plants, which in turn depend on nitrogen
intake (IPCC 2001 ).
Most plants obtain carbon, their major con-
stituent, via photosynthesis from atmospheric
CO 2 , and more CO 2 usually benefi ts plant growth.
Before industrialization, around the year 1750,
levels of CO 2 in the air were at 280 ppm; in 2005
it reached 380 ppm, and a level of 560 ppm can
be expected by the end of the twenty-fi rst century
(IPCC 2007 ).
Computer models, which calculate future
yields under climate change, usually incorporate
increasing atmospheric CO 2 as the “fertilization
effect.” Experiments with elevated CO 2 indeed
show increased biomass production and crop
yields for most plants. However, higher yields in
tons per hectare might be useless, when the nutri-
tional value of the harvest is much lower.
Cotrufo et al. ( 1998 ) evaluated 75 studies on
nitrogen/protein content under elevated CO 2 and
found that nitrogen concentrations were reduced
by an average of 9 % (for belowground tissues) to
a 14 % (for aboveground tissues). While Cotrufo
et al. ( 1998 ) evaluated studies on all kinds of
plants, Loladze ( 2002 ) looked more specifi cally
at food crops. His results show an average nitro-
gen reduction of 15-20 % as well as substantial
reductions of other important micronutrients
such as zinc and iron. A meta-analysis of 228
experimental observations (elevated CO 2 com-

pared to ambient CO 2 ) of barley, rice, wheat,
soybean, and potato showed a reduction of grain
protein concentration of 10-15 % in wheat,
barley, and rice. The reduction in potato tuber
protein concentration was 14 %. For soybean,
there was a much smaller reduction of protein
concentration of 1.4 %. There is a general trend
of nitrogen reduction (6 %) for rice, but no
signifi cant reduction of zinc and iron.
In response to Loladze ( 2002 ), other research-
ers investigated the experimental settings of
enriched CO 2 experiments and analyzed rice
grain samples from an open-fi eld experiment.
Quite opposite to Loladze ( 2002 ), the analysis
showed increased micronutrient content in rice
grains from the fi eld with elevated CO 2 . They
argue that the reduction of micronutrients
observed in other experiments is likely due to
reduced nutrient availability in experimental soils
and/or in limited root growth in pots.
The analysis of numerous studies on the grain
quality of wheat under elevated CO 2 confi rmed
the lower protein levels and suggests that protein
concentrations in wheat grains may decrease to
values below the minimum quality standard for
bread-making. Signifi cantly lower concentra-
tions of amino acids, zinc, iron, and other nutri-
ents were also detected, but these reductions were
observed only in chamber experiments, which
were criticized.
However, while it is not clear if higher CO 2
levels decrease the content of micronutrients, it
seems very clear that the protein content is sig-
nifi cantly reduced in most crop plants. Therefore,
results of computer models which calculate
yields in metric tons must be interpreted with
caution, with regard to food security. It would be
much more useful to have results in energy units
(Calorie or Joule) instead of tons/ha.

4.12 Sea-Level Rise

Sea-level rise is an inevitable consequence of a
warming climate owing to a combination of ther-
mal expansion of the existing mass of ocean
water and addition of inundation of coastal land,
especially where the capacity for introduction or