of carbon dioxide, which is increasing by approximate-
ly 1.5 to 2.0 parts per million per year as a result of the
combustion of fossil fuel, deforestation and soil erosion.
Possible climate changes are projected to influence
energy resources, dislocate agriculture, melt the ant-
arctic ice caps, raise sea levels and sink coastal cities.
Such projections have captured the attention and
imagination of scientists and the public (Environmen-
tal Protection Agency, 1983; National Academy of
Sciences, 1983a). So far these projections have not been
verified in the real world by any detected climatic
change.
 Elevated levels of atmospheric COz also have
biological effects that should be studied. Though some
of these appear positive and may have already oc-
curred, ,:;u.. u ., indom mentioned. We know a great
deal about how crops in controlled environments re-
spond to increases in atmospheric carbon dioxide up to
double or triple present levels. All major crops in short-
term experiments have yielded better and grown more
rapidly when given increased CO under otherwise
identical conditions of sunlight, soil fertility, water
supply and temperature, and in the absence of
devastating pests. This perspective is absent in almost
all writings on the CO2 issue. Obviously, more research
is needed. There may be some surprises in the ability
of C3 and C4 weed and crop plants to compete with
each other. Elevated levels of atmospheric CO2 may
also alleviate water, high temperature, light and air
pollutant stresses. Other important potential benefits
are better use of water by plants and the extension of
boundaries for crop production into arid lands, with
implications for reductions in desertification.
CO2-induced higher temperatures, as well as elevated
levels of atmospheric CO, themselves, may have great
effects on the relationships between crops and pests.
Some noxious weeds, such as Portulaca oleracea (a suc-
culent), would likely be favored by higher tempera-
tures. On balance, the many positive effects of in-
creases in atmospheric CO2 may be offset by unfavor-
able water and temperature changes (Wittwer,
1983b).
 The potentially important biological effects of a ris-
ing level of atmospheric CO2 on plants were the subject
of a major international conference May 23-30, 1982,
at the Russell Center in Athens, Ga. (Lemon, 1983).
Because of the potential for rising levels of atmospheric
CO (2 ppm/year) to have major effects on U.S. and
global biological production, including food, fiber and
forestry products, a NASA or Manhattan-type project
or program is needed to research photosynthetic proc-
esses and the consequences of rising levels of atmos-
pheric carbon dioxide.
 Atmospheric Pollutants and Trace Elements-
Evidence is mounting that air pollutants can have both


positive and negative effects on crop production (Heck,
et al., 1982). These pollutants include sulfur and
nitrogen compounds, ozone and carbon dioxide in the
atmosphere, as well as acid deposition, all of which
have confirmed effects on the productivity of agricul-
tural crops, rangelands, lakes and forests (National
Academy of Sciences, 1982b). It will become increas-
ingly important for American agriculture to identify
accurately the sources of air pollutants, monitor
changes, assess their effects on resource productivity,
and seek means to reduce adverse sensitivities of
agricultural crops to them. Some progress is being
made in identifying chemicals to reduce the damage.
 Four points are important with respect to needed
DISC research in this area:
 First, the effects are regional and have profound
political and economic consequences. Various regions
of the United States and the world may respond dif-
ferently to pollutants.
 Second, the effects are subtle. Acid rainfall is an
example where effects may not be observed for
decades. As yet, no evidence exists that it is harming
agricultural crop productivity in the United States.
 Third is the issue of multiple pollutants, which is
often the situation under real world conditions. Seldom
can we address the effects of a single substance.
 Fourth, air pollutants originating with human
activity can interact with environmental constraints,
such as the droughts and biological stresses of natural
systems.
 One of the environmental issues of greatest concern
to the American and Canadian publics is acid rain. Its
effects, either short- or long-term, on productivity of
renewable resources (agricultural, lakes, fish, forests,
range) are not known. Understanding changes in
atmospheric constituents, atmospheric depositions and
their effects on plants, animals and fish is an important
challenge for disciplinary, biological and physical
science researchers. Such understanding is clearly rele-
vant for food production, agriculture and forestry.
 Biological Nitrogen Fixation Chemical fertilizer is
the most important industrial input for agriculture.
Chemical nitrogen fixation uses more energy than is
needed for any other agricultural input. The energy
used-mostly natural gas in the fixation process-is
non-renewable. This energy is used to convert nitrogen
from the air into a form plants can use. A modern
nitrogen fertilizer factory consumes approximately one
cubic meter of natural gas for each kilogram of nitro-
gen that produces ammonia. Up to 35 percent of the
total output of all crops on earth is ascribed to this
single input. The global use of chemically fixed
nitrogen fertilizer for crop production has grown