Final answer:
Anthropogenic water vapor is not considered a significant contributor to global warming due to its short atmospheric residence time and because its global concentration is mainly temperature-dependent, not directly affected by human activities.
Step-by-step explanation:
When fossil fuels are burned, water vapor is produced. However, anthropogenic water vapor is not a significant factor in global warming for several reasons. First, it has a short residence time in the atmosphere meaning it does not stay in the atmosphere long enough to have a substantial warming effect.
Second, water vapor is controlled by temperature which affects evaporation and precipitation rates; thus, the global concentration of vapor responds to the temperature rather than human activity. Lastly, it's essential to understand that while water vapor is a potent greenhouse gas, the overall levels of vapor in the atmosphere are mainly dictated by the water cycle and are in balance with the planet's temperature, which human-produced water vapor does not significantly disrupt.