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 CO2 still constitutes only a tiny fraction of 1% of the atmosphere. Rising CO2 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 CO2 from water (e. g., from the oceans). To conclude that increased CO2 causes global warming, therefore, would be to confuse cause with effect.