A new study shows just how important the ozone layer is to the living world. Without it, the planet would be 3.5° colder than it is today, and temperatures would approach ice age levels. In this case, the amount of carbon dioxide would remain unchanged. According to the authors of the work, the main effect of ozone deficiency will be cooling of the upper layers of the stratosphere. Colder air cannot hold as much moisture, so the stratosphere will become drier. Water vapor is an important greenhouse gas, so without it the Earth’s overall greenhouse effect would be reduced.