A related canard is that CO2's warming effect is limited because at higher concentrations it saturates the atmosphere and can absorb only so much solar radiation or heat from Earth's surface. Global warming skeptics have used this argument to erroneously explain why Earth stops warming up after an ice age. But the reality is that CO2 disperses to other layers of the troposphere—the greenhouse blanket becomes thicker—so that the absorption capacity is not diminished, Mann says.