Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels? Assuming that the CO2 level continues to increase with time, how likely are plants to be able to continue to adapt by adjusting stomatal conductance?