Water vapor also acts as a greenhouse gas, yet it is not often talked about in the media with respect to climate change. Why are scientists more concerned about the impact of CO2 in the atmosphere than water vapor? Based on the concept of humidity, the amount of water vapour in the atmosphere is a response to the temperature, not the main driver of temperature change. Carbon Dioxide is present in much larger amounts in the atmosphere than Water Vapour Water Vapour is not really a greenhouse gas Water Vapour is decreasing in proportion as the atmosphere warms up