A favorite global warming denier's spiel to put our minds at ease is to assure us that "CO2 is good for you."
The claim that the greenhouse gas carbon dioxide is not a pollutant but an integral part of the earth's atmosphere and the major food source for plants omits one crucial factor--too much of a good thing can be bad.
Conservative media outlets produce numerous stories asserting that contrary to climate change Cassandras, the more carbon dioxide emitted into the air by human activity, the better. Plant life will flourish accordingly.
In a controlled indoor greenhouse environment where water supply and fertilizer can be artificially manipulated, excess carbon dioxide can be utilized to increase the pace and productivity of crop growth. But outside the confines of an agricultural greenhouse, it is a different proposition. Ever increasing concentrations of carbon dioxide from the burning of fossil fuels are already approaching levels that will adversely impact both human and plant life over the long term.
Beyond the walls of the greenhouse enclosure, human beings cannot control the climate. Greenhouse gas emissions from fossil fuel combustion have already raised global temperature to levels with strong circumstantial links to prolonged drought that has diminished land suitable for crops.
Hence, CO2 in excess is already an indirect pollutant by altering weather in ways detrimental to agricultural productivity. It also has indirect harmful effects on human beings, given that warmer temperatures enable tropical diseases to migrate northward and expand the scope of their affliction.
More to the point of contention, excess carbon dioxide has a direct effect on plants that is not the beneficial intervention that global warming deniers would have us believe. Heavy CO2 Exposure makes the plant work harder to grow, causing it to lose nutritional content in the process. Soaring concentrations of carbon dioxide above levels we now have also can reduce photosynthesis. They can trigger growth spurts that are so rapid that some plants perish from being unable to adapt while others become more vulnerable to fatal insect predation. And it's not just plants that are effected. High concentrations of CO2 are absorbed by the oceans, pressuring their storage capacity and thus contributing to their increasing acidity.
Oh yes, excessively high levels of carbon dioxide in the atmosphere can also have direct adverse effects on human health as well, ranging from headaches and dizziness to convulsions and fatal comas if the concentrations really get out of hand and reduce the necessary percentage of oxygen in the atmosphere.
In the short run, warmer global temperatures resulting from fossil fuel combustion may temporarily expand agricultural zones and growing seasons. But if global warming is allowed to proceed unchecked, and ancillary protracted drought becomes chronic, there will be a severe contraction of arable land and the food it supplies to humanity.