Final answer:
The ozone layer's recovery is slow because CFCs have a long atmospheric lifetime and therefore continue to deplete the ozone even after emissions have declined. International efforts like the Montreal Protocol have helped reduce CFC emissions, but complete recovery will take many decades due to existing CFCs and the management of CFC "banks".
Step-by-step explanation:
The reason it will take years for the ozone layer to recover, even though the use of CFCs has declined significantly, is that CFCs persist in the atmosphere for an extended period, causing continued ozone depletion. CFC molecules are long-lived and can survive in the stratosphere for decades, where they continue to break down ozone molecules. Each chlorine atom, released from the CFCs, can destroy ozone for up to two years before being neutralized. Additionally, the Montreal Protocol has been successful in reducing CFC emissions, but there is still the issue of CFC "banks", where older equipment can leak CFCs into the atmosphere.
Since the introduction of the Montreal Protocol in 1987, there have been notable improvements in the state of the ozone layer. However, given the long life of CFCs and their continued presence in the atmosphere, the process of recovery is very slow. Ozone holes have started to shrink, and signs of recovery are evident, but full restoration is not immediate and is expected to take decades.
Moreover, emissions from certain regions and the variability of atmospheric conditions mean that there remains substantial risk and variability in the ozone layer's recovery. The ozone layer's recovery is not solely dependent on CFC emissions but also on the global cooperation in managing existing CFC reserves and preventing new ones from being released.