When more water vapor works its way into the stratosphere, the water molecules can be broken down, releasing reactive molecules that can destroy ozone. If the trend of increasing stratospheric water vapor continues, it could increase future global warming and impede ozone stratospheric recovery. The impact on global warming comes about because both water vapor and ozone are greenhouse gases, which trap heat leaving the Earth. When they change, the Earth's energy balance changes too, altering the surface climate. Increased water vapor in the stratosphere makes it warmer on the ground by trapping heat, while the ozone loss makes it colder on the ground.
Water vapor has a much larger effect, so that overall the changes increase global warming.
Although ozone depletion cools the Earth's surface, repairing stratospheric ozone is important to block harmful ultraviolet radiation. Other greenhouse gas emissions also need to be reduced. The spacecraft's mission at launch was to improve understanding of stratospheric ozone depletion by analyzing vertical profiles of ozone, hydrogen chloride, hydrogen fluoride, methane, water vapor, nitric oxide, nitrogen dioxide, and aerosols. Fourteen years of lower stratospheric measurements have revealed large increases in water vapor. Though some older studies conflict with lower stratospheric observations of water vapor trends, new studies agree with the increases, showing they have been taking place for more than four decades.