NOAA 2006-096
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Answers to questions about ozone depletion and the recovery of the ozone hole are now easy to find by researchers as well as the general public, through a new online index developed by NOAA’s Earth System Research Laboratory in Boulder, Colo.

The Ozone Depleting Gas Index (, uses simple graphs and charts to track progress in reducing the threat to Earth’s ozone layer—the protective shield that prevents harmful ultraviolet radiation from reaching the surface. A new chart shows which of the harmful gases are declining, which are still increasing, and the overall effect of these changes. Scientists will update the index every year using new data collected from NOAA’s global observation network.

The index is a number between zero and 100 that tracks the relation between the decline of ozone-depleting gases and the low targeted level of these gases where no ozone hole should exist. The index also illustrates when the ozone hole and the ozone layer at midlatitudes will fully recover if nations continue to reduce their use of these gases.

“I like to think of it as a 100-yard football field,” said David Hofmann, director of ESRL’s Global Monitoring Division. “For full recovery, we have to run those 100 yards. The 2005 data indicate that we’re still on our own 12-yard line, with 88 yards still to go, for Antarctic ozone hole recovery. For midlatitude ozone recovery, we’ve reached our own 23-yard line. We’ve got a long way to go in both cases.”

The ODGI consists of two indexes. One tracks the Antarctic ozone hole itself. The other tracks ozone depletion over the midlatitudes – where a majority of the Earth’s population lives. Both the midlatitude and the Antarctic indexes are based on NOAA’s gas measurements at Earth’s surface, but it takes longer for chemicals at the surface to reach the more distant Antarctic stratosphere. Also, chemical transformations occur at different rates in the two regions. Two indexes are needed to accurately capture these measurements.

Hofmann estimated that the Antarctic ozone hole should be gone by the years 2075–2080. The midlatitude ozone layer should recover by about 2045–2050. However, other factors, such as climate change, could affect long-term recovery, he cautioned.

Monitoring greenhouse gases falls under NOAA’s goal to “understand climate variability and change to enhance society’s ability to plan and respond.”

NOAA, with cooperation from NASA, uses a variety of sensors either on the ground or transported through the atmosphere by aircraft, satellites and balloons, to monitor ozone-depleting gases and ozone itself. The information collected over the past 25 years has been used extensively in international assessments of the science of ozone layer depletion, but the public and policymakers haven’t had easy access to a simple, updated status report.

“We designed the Ozone Depleting Gas Index to make it easier for the public to follow the worldwide effort to save the ozone layer,” said Hofmann.

Though simple to view online, the index is based on complex measurements and calculations. Chemicals containing both chlorine and bromine have been measured regularly for the past 15 to 25 years at NOAA sites across the globe. While chlorine compounds are more plentiful, those containing bromine are more efficient at destroying ozone molecules in the upper atmosphere. To account for this higher efficiency, NOAA scientists converted the bromine chemical measurements into their equivalent in chlorine and combined them into one number they call “effective equivalent chlorine” levels. They assigned 100 as the maximum level of ozone-depleting gases, as measured in 1994, and zero as the level of those gases necessary for full recovery of the ozone layer in the future.

In 2007 the National Oceanic and Atmospheric Administration, an agency of the U.S. Commerce Department, celebrates 200 years of science and service to the nation. From the establishment of the Survey of the Coast in 1807 by Thomas Jefferson to the formation of the Weather Bureau and the Bureau of Commercial Fisheries in the 1870s, much of America's scientific heritage is rooted in NOAA.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and information service delivery for transportation, and by providing environmental stewardship of our nation's coastal and marine resources. Through the emerging Global Earth Observation System of Systems (GEOSS), NOAA is working with its federal partners, more than 60 countries and the European Commission to develop a global monitoring network that is as integrated as the planet it observes, predicts, and protects.

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