Here is what IPCC was refering to. As you are by now aware, increasing CO 2 concentrations in climate models increases the temperature of the atmosphere. Because of the complexities of radiative transfer of energy, an increase in CO 2 leaves a particular signature on the temperature as a function of height in the atmosphere. The new development is the addition of other greenhouse-active gases to the model simulations, and the main players are sulfate aerosols and ozone.
Ozone is a bit confusing because it has a dual impact in the environment.
On the one hand, ozone is nasty to breath, and we'd like to keep the concentration of ozone low in tropospheric air, which is why we put catalytic converters on cars. On the other hand, ozone in the stratosphere absorbs ultraviolet light which could otherwise cause skin damage and crop damage and other problems, so we'd like to keep concentrations in the stratosphere high. So the ozone concentration in the stratosphere has been decreasing, while tropospheric concentrations are increasing somewhat. The major effect of decreasing stratospheric ozone is a cooling, which is caused by the decrease absorption of ultraviolet light in the stratosphere. In fact, heating by ozone getting zapped by UV is why there is a stratosphere, which gets warmer with height, in the first place.