Final answer:
Rising atmospheric CO₂ increases the greenhouse effect by absorbing more radiation, requiring the Earth's surface to warm further in order to maintain energy balance. This causes global warming, especially as higher temperatures increase water vapor, another greenhouse gas.
Step-by-step explanation:
Increasing atmospheric carbon dioxide (CO₂) amplifies the Earth's greenhouse effect by trapping more heat. As CO₂ levels rise, the altitude at which radiation is emitted to space also rises, since warmer air holds more CO₂ and thus absorbs more radiation. Due to the temperature decrease with altitude in the troposphere, emission from these higher altitudes is less effective, requiring the Earth's surface to warm further in order to maintain the energy balance between incoming solar radiation and outgoing emission. With more CO₂, the Earth's surface temperature increases, a process known as global warming. Furthermore, the increase in surface temperature leads to higher water vapor in the atmosphere, which in turn intensifies the greenhouse effect because water vapor is also a greenhouse gas. Consequently, Earth's average surface temperature has risen, and the increased concentrations of CO₂ from fossil fuel burning contribute significantly to this trend.