The Specter of Species Extinction
XII. Conclusions
The CO2-induced global warming extinction hypothesis claims that as the world warms in response to the ongoing rise in the air's CO2 content, many species of plants and animals will not be able to migrate either poleward in latitude or upward in elevation fast enough to avoid extinction as they try to escape the stress imposed by the rising temperature. With respect to plants, however, we have shown that as long as the atmosphere's CO2 concentration rises in tandem with its temperature, most of them will not "feel the heat," as their physiology will change in ways that make them better adapted to warmer conditions. Hence, although earth's plants will likely spread poleward and upward at the cold-limited boundaries of their ranges in response to a warming-induced opportunity to do so, their heat-limited boundaries will probably remain pretty much as they are now or shift only slightly. Consequently, in a world of rising atmospheric CO2 concentration, the ranges of most of earth's plants will likely expand if the planet continues to warm, making plant extinctions even less likely than they are currently.
Animals should react much the same way. In response to concurrent increases in atmospheric temperature and CO2 concentration, they will likely migrate poleward and upward, where cold temperatures prevented them from going in the past, as they follow earth's plants. Also as with earth's plants, the heat-limited boundaries of their ranges should in many cases be little affected, as has been observed in several of the real-world studies that have been wrongly cited as providing evidence for impending species extinctions, or their entire ranges may simply shift with the rising temperature, as has been observed in many real-world studies of marine ecosystems.
To summarize, both theory and observation paint the same picture. A goodly portion of earth's plants and animals should actually expand their ranges and gain a stronger foothold on the planet as the atmosphere's temperature and CO2 concentration continue to rise. If the air's CO2 content were suddenly to stop increasing, however, the biosphere could find itself facing a significant challenge, as the world's plants would cease acquiring the extra physiological protection against heat stress that is afforded them by rising atmospheric CO2 concentrations. Consequently, the end result of curtailing anthropogenic CO2 emissions might well be just the opposite of what many people are hoping to accomplish by encouraging that policy, i.e., many species might actually be driven to extinction, rather than being saved from such a fate.