Chincoteague, Virginia: on hurricane aircraft field mission at the Wallops Island Flight Facility, Paul Newman responds to the key questions on 14th Sept 2013.
Rajendra Shende, Chairman TERRE and former Director UNEP, on the occasion of International Ozone Day -2013 had chat with Paul Newman of NASA. Question-Answers follow:
1. How do you compare the present status of the Stratospheric Ozone Layer with last two decades?
The ozone layer continued to decline and threaten life on the earth till the late 1990s, but that decline stopped about 10 years ago thanks to the world wide actions to phase out ODS, which resulted in a decline in chlorine loading in the stratosphere.
However, the evidence of the start of a return of the Ozone layer to the pre-1980 state is a bit thin at present. There is a lot of year-to-year variability of ozone, and this variability masks the expected slow upward ozone trend.
2. When MP came into effect there was famous graphical curve presented by the Scientific Assessment Panel of WMO and UNEP which depicted ‘peaking and then tapering off’ the chlorine loading and hence ozone depletion. Do you consider that curve is being traced well by the humanity action?
ODSs are clearly declining in our atmosphere. Ground stations show that nearly all ODSs are falling. We have satellite measurements that also show that chlorine levels in the stratosphere are decreasing. There are still a few odds and ends about these declines. For example, a chlorocarbon (carbon tetrachloride) is declining at a slower rate than scientists expect, but even this gas is decreasing in our atmosphere.
The observations generally follow that famous graphical curve of peaking and tapering off. The observations show that the peak occurred around 1996, and now tapering off. The slow decline of ODSs is because these chlorofluorocarbons (CFCs) have very long atmospheric lifetimes. For example, the lifetime of a CFC-12 molecule in the atmosphere is about 100 years.
3. Have we peaked in Ozone layer depletion and chlorine loading?
Yes. We’re clearly “over-the-hump”. Hard to say if ozone layer is getting better yet. There is some evidence, but not conclusive. In short, while chlorine loading observed is as per the predicted model, but corresponding Ozone recovery is not yet evident.
4. Is there a good and high probability that inaction on climate change is resulting into slow recovery of Ozone Layer?
Carbon dioxide increases will cause the upper stratosphere to substantially cool, and this will lead to a stronger ozone recovery in the upper stratosphere.
In the lower stratosphere, the problem breaks into two parts: the tropics and the mid-latitudes. In the tropics, climate change will slow ozone recovery due to a changing circulation, and possibly causing ozone to decrease. In the mid latitudes, climate will cause ozone to increase beyond its natural level.
However, over all we can say that inaction to address climate change will result in a different stratosphere and ozone layer.
5. What is your key message as key ozone scientist to policy makers at this juncture?
Don’t lose focus. First, we need to continue to watch the stratosphere to understand if our policies are working. Second, we need to maintain the provisions of the Montreal Protocol in order to insure the recovery. Third, we need to start looking at the individual impacts of climate compounds, including HFCs. They may not affect ozone directly, but they will change the stratosphere, and therefore the ozone layer.