Earth's Ozone Layer Starting to Heal

BOULDER, Colorado, May 8, 2006 (ENS) – Over the past 20 years, nations worldwide have controlled the production and use of ozone-destroying chlorine compounds, and the Earth's atmosphere appears to be recovering from losses of protective ozone in the upper atmospheric layers, according to new research.

A paper by Betsy Weatherhead of the U.S. National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory in Colorado and Signe Bech Andersen of the Danish Meteorological Institute documents a leveling off of ozone loss as a result of the Montreal Protocol.

One hundred eighty countries have signed this international agreement, which was first enacted in 1987 to limit emission of ozone-depleting chemicals into the atmosphere.

The protocol, to which the United States is a party, calls for phasing out production and consumption of compounds that deplete ozone in the stratosphere - chlorofluorocarbons (CFCs), halons, carbon tetrachloride and methyl chloroform. This was accomplished in 2000 for most of the listed substances and in 2004 for methyl chloroform.

"Ozone in the upper atmosphere protects life on Earth from harmful solar rays,” Weatherhead said, “and a thinning of ozone – even total depletion in some areas – has been a concern since the 1970s."

The latest measurement of the ozone layer in the Northern Hemisphere, taken May 6, 2006, shows the hole is smaller than in previous years at this time. (Image courtesy NOAA)

But ozone is constantly created, destroyed and transported in the atmosphere, Weatherhead says. As pollutants filter out of the atmosphere, the ozone layer naturally rebuilds.

NOAA uses satellite, airborne and ground-based systems to continuously monitor stratospheric ozone as well as the chemical compounds and atmospheric conditions that affect its concentration. Data from NOAA, from NASA and from a global monitoring network have shown that chlorine has leveled off in the atmosphere, and now show that ozone loss is leveling off, too.

Still, stratospheric ozone remains at below-normal levels at all latitudes, so ultra-violet (UV) rays from the sun are higher than they should be. The scientists advise that people continue to protect themselves from UV rays when they are outdoors.

The first signs are hopeful, but Weatherhead emphasizes that the recovery process is still in early stages. Unusual temperatures or a large volcanic eruption could cause the polar ozone holes to expand again.

"In these early stages of recovery, it can often be difficult to say what causes long-term changes because the atmosphere is so complex," said Weatherhead.

"To be confident that the ozone layer is recovering, we need more than just an increase in ozone," she said. "We need the changes to agree with observations of the other factors that can influence ozone levels."

Atmospheric scientist Betsy Weatherhead at her computer. (Photo courtesy CIRES)

The paper is the first to show that positive changes in the ozone layer are in general agreement with what is expected due to changes in chlorine levels in the upper atmosphere.

Weatherhead says she and colleagues are seeing signs of ozone recovery "in the right seasons, in the right latitudes and at the right altitudes." She called these positive signs a success story for international action to protect the environment.

"Because the Montreal Protocol was enacted to control chlorine,” she added, “the atmosphere is having a chance to recover."

The Earth System Research Laboratory consolidated the previous six NOAA laboratories into a center in Boulder, Colorado, as of October 1, 2005. The lab includes four divisions: Global Monitoring, Physical Sciences, Chemical Sciences, and Global Systems.

"This single laboratory will help NOAA better deal with the research challenges of this new century, in which the environmental issues we face cross the traditional disciplinary boundaries and demand a whole Earth perspective," said Richard Rosen, assistant administrator for NOAA's Office of Oceanic and Atmospheric Research.