A review of the scientifi c literature concerning the environmental consequences of increased levels of atmospheric carbon dioxide, the most prominent greenhouse gas contributed by human activities, leads to the conclusion that increases during the twentieth century have produced no deleterious effects upon global climate or temperature. Increased carbon dioxide has, however, markedly increased the growth rates of plants as inferred from numerous laboratory and field experiments. There is no clear evidence, nor unique attribution, of the global effects of anthropogenic CO2 on climate.

Meaningful assessments of the environmental impacts of anthropogenic CO2 are not yet possible because model estimates of global and regional changes in climate on interannual, decadal and centennial time-scales remain highly uncertain.