Top scientists, policy makers and industry leaders are gathering in Washington this week for a four-day symposium that will feature discussions about the past, present and future health of the ozone layer. Some key questions on the agenda: To what degree are climate change and ozone depletion interconnected? And how can leaders apply lessons learned while confronting the ozone problem that dominated headlines in the 1980s to the threats posed by global climate change? In 1987, delegates from 24 nations signed the Montreal Protocol, a landmark piece of legislation that set limits on emissions of ozone-depleting substances known as chlorofluorocarbons (CFCs). Since then, every country in the world has followed suit. The video above shows what could have happened if countries had failed to regulate CFCs. But while the Montreal Protocol began the process of closing one chapter of the ozone story, the ozone layer still requires careful monitoring because other substances in the atmosphere – including climate-altering greenhouse gases – can also affect it. 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. To see daily updates on the health of the ozone layer, please visit Ozone Hole Watch.
The ozone layer is on the road to recovery. Why is it still such a hot topic among scientists?
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 the stratosphere.
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 stratosphere.
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 recovery.”
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 effective policy.
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.