Even if one assumes that the increase in atmospheric carbon dioxide
caused by human activities has no effect on global warming, it is a
symptom of rapid destruction of rainforests and excessive and
inefficient use of fossil fuels. Many negative aspects of fossil fuel
use are quite clear including acid rain, much of several other types of
air pollution (ozone, peroxyacetyl nitrate or PAN) and its negative
effects on human health and the environment, coal strip mining and its
associated water pollution and habitat destruction, and the
environmental damage caused by oil spills and oil drilling.

The idea that increases in atmospheric carbon dioxide will increase
plant growth is not always supported by recent research. That is not
surprising given that under natural conditions plant growth is often
limited by factors other than low carbon dioxide levels, such as lack
of water and lack of mineral nutrients. Research has also shown that
even when higher carbon dioxide levels increase crop growth, the crops
may have less nutritional value.

David R. Hershey

References

Carbon dioxide fertilization is neither boon nor bust
http://www.newswise.com/articles/view/503175/

A shrinking sink? Carbon fertilization may be flimsy weapon against
warming
http://www.innovations-report.com/ht...ort-25846.html

Rising carbon dioxide could make crops less nutritious
http://www.scidev.net/News/index.cfm...9&language =1