Carbon dioxide, it should be emphasized, is not a pollutant, but a natural component of the atmosphere, which is necessary to plant life and therefore all life on earth. While the global-warming hypothesis remains totally unproven, it is indisputable that atmospheric carbon-dioxide levels have risen in recent decades, although CO
2 still constitutes only a tiny fraction of 1% of the atmosphere. Rising CO
2 levels, indeed, are believed to have contributed significantly to agricultural production since World War II, helping to avert famine in much of the world. It should also be acknowledged that over a long span of geological time atmospheric carbon-dioxide concentrations have correlated positively with global temperatures. This correlation, however, simply reflects the easily demonstrable fact
(more information) that rising temperatures lead to a release of CO
2 from water (e. g., from the oceans). To conclude that increased CO
2 causes global warming, therefore, would be to confuse cause with effect.