There are a number of environmental stresses that can severely restrict plant growth and development; but they have little detrimental impact on the benefits provided to such plants by atmospheric CO2 enrichment. In the case of soil salinity, for example, the percentage growth enhancement due to an increase in the air's CO2 content is about the same in both salt-stressed and non-salt-stressed plants. In the presence of harmful air pollutants, on the other hand, the percentage growth enhancement produced by atmospheric CO2 enrichment is typically even greater
than it is in non-polluted air. And as air temperatures rise higher and higher, so too do the relative benefits of elevated CO2 concentrations rise higher and higher. At the point where plants normally succumb to thermal death, in fact, the presence of high CO2 levels often helps them to survive, where normally they would wither and die.
The preferred or optimum temperature for growth in most plants also rises with an increase in the CO2 content of the air; and it generally rises even faster than the rate of global warming that is typically predicted to accompany an increase in atmospheric CO2. Consequently, and contrary to the claims of many people who are unaware of this fact, if there were ever to be a CO2-induced warming of the globe, there would be no mad rush of plants to keep up with the poleward shift of the climatic regimes to which they are currently accustomed. And there would likewise be no extinctions of migratory laggards!
At the other end of the temperature spectrum, there are a number of ways by which atmospheric CO2 enrichment may mitigate chilling injury to plants. Higher CO2 levels also help plants to better withstand air-borne and soil-borne plant pathogens; and, in the mean, they help crops somewhat more than they help the weeds that compete with them. Insects will probably always be a problem, even in a CO2-enriched world; but with the greater levels of vegetative productivity that are typical of such an environment, there should be more organic matter available to accommodate them, so that Earth's plant life should not suffer any worse in this regard than it does now.