NASA November 8,
2011 -In the Q & A below, NASA Goddard atmospheric scientist Paul Newman offers
his perspective on why the ozone story isn’t over, and how climate change will
likely impact the evolution of the ozone layer in the future.
ozone layer is on the road to recovery. Why is it still such a hot topic among
It’s important to continue monitoring ozone because it’s so vital to life on
Earth. Surface measurements and satellite observations confirm that ozone isn’t
declining in our atmosphere anymore, so the Montreal Protocol is working. But
ozone is impacted by many factors, not just CFCs. The Earth’s natural variations
– like volcanic emissions, climate change, and the sun – can all impact ozone.
Also, technological innovations like high-altitude aircraft or industrial
chemicals can also impact it. So the ozone story isn’t over. It’s evolving.
If all of these factors influence ozone, can we say with certainty how it will
change in the future?
The ozone layer is recovering from the effects of CFCs, but because of climate
change, it will recover to different levels than its natural pre-industrial
state. Our models show that we’re not going back to the old ozone layer, we’re
going back to some new version of it. Our models also show that climate has a
very different impact on ozone depending on whether you’re in the troposphere or
What’s the difference between the troposphere and the stratosphere?
The troposphere is the lowest layer of our atmosphere, on average, extending up
to about 7 miles above the Earth’s surface. Our day-to-day weather happens in
the troposphere. The stratosphere extends from about 7 to 30 miles above the
surface. While ozone is extremely important for screening harmful solar
ultraviolet (UV) radiation, it’s a dangerous air pollutant at the Earth’s
surface. Fortunately, about 90 percent of the planet’s ozone is in the
stratosphere, while only 10 percent of is in the troposphere
What about greenhouse gases? Do they also have different effects in the
troposphere and stratosphere?
Greenhouse gases have much different effects in the troposphere and
stratosphere. Carbon dioxide both absorbs and emits infrared radiation. In the
troposphere, increased levels of carbon dioxide and other greenhouse gases block
outgoing radiation, increasing the surface temperature. In the stratosphere, the
increasing carbon dioxide concentrations allow greater radiation to space,
cooling the stratosphere. So greenhouse gases warm the surface and cool the
How will climate change affect ozone in the stratosphere?
In the lower stratosphere, climate change will decrease the local ozone levels
in the tropics and increase ozone in the mid-to-high latitudes. The “total
ozone” will increase over its natural levels in the mid-latitudes in both the
Northern and Southern Hemispheres – what some scientists call a “super
How do you think the lessons learned from the ozone hole story are relevant to
the climate change story?
There are two important science lessons from the Montreal Protocol. The first
lesson is that solid science is the foundation for policy. The quality of both
ground and satellite ozone observations can now detect a 1 percent change over a
10-year period. Policy makers relied on these estimates from scientists to
formulate options on the regulation of ozone depleting substances. As the
science evolved, the Montreal Protocol was strengthened. The science of climate
change has seen similar improvements over the last few decades. Scientists
continue to improve the quality of both observations and models of climate
change. The improved quality of the science allows for the formulation of
What’s the second lesson?
The Montreal Protocol demonstrates that the nations of the world can act
together to solve a global problem. National boundaries are irrelevant to the
stratospheric ozone layer. Emissions from countries in the Northern Hemisphere
mainly caused the Antarctic ozone hole in the Southern Hemisphere. The nations
of the world recognized the problem and acted together. This involved efforts
between policy makers, technologists, scientists, industry, and non-governmental
organizations. Technologies for replacing ozone-depleting substances have now
been developed, and levels of these substances are now decreasing in our
atmosphere. But we need to continue monitoring ozone and tracking how it reacts
to climate gases. The story isn’t over.
by Alison Ogden, Adam Voiland. NASA