Ozone in Earth's stratosphere at an altitude of approximately 20 km in mid-March 2011, near the peak of the 2011 Arctic ozone loss.
Credit: NASA/JPL-Caltech
Chlorine monoxide – the primary agent of chemical ozone destruction in the cold polar lower stratosphere – for the same day and altitude.
Credit: NASA/JPL-Caltech
DUBLIN: A hole in the ozone layer has been detected over the Arctic for the first time.
An unprecedented loss of ozone occurred during the northern winter of 2011 and this is potentially bad news for human health, according to international team that reported the discovery this week in the journal Nature.
The stratospheric ozone layer extends from about 15 to 35 km above Earth's surface and protects life from the Sun's harmful ultraviolet (UV) rays. Depletion of ozone in this layer is associated with higher exposure at the surface to UV, which is known to be associated with adverse health and ecosystem impacts, said co-author Gloria Manney at NASA's Jet Propulsion Laboratory in Pasadena, California.
Ozone-destroying chemicals
Extremely cold conditions in the atmosphere trigger reactions that transform chlorine into forms that chemically obliterate ozone. The necessary conditions occur every winter in the Antarctic stratosphere, where a hole in the ozone first caused alarm in the mid-1980s, with depletion observed in spring. The chlorine originates from man-made compounds.
Until now, the Arctic winter stratosphere has been much warmer than the Antarctic's, with conditions of low temperature not persisting for long enough to allow extensive ozone destruction. The cold period in the Arctic stratosphere lasted much longer in late 2010 to early 2011, however, allowing ozone-destroying forms of chlorine to linger and destroy more ozone. A loss of 80% of ozone was observed at an altitude of 18 to 20 km.
The discovery came after analysis of observations from satellite instruments and from balloon-borne ozone sensors. The international team concluded, "For the first time, sufficient loss occurred to reasonably be described as an Arctic ozone hole."
Unprecedented event
This is the first report of chemical ozone destruction over the Arctic which is comparable to that in the Antarctic ozone hole. No previous year rivals 2011 in the Arctic for the loss of this protective ozone blanket.
Reduced overhead ozone means more UV at the Earth's surface, which is known to have adverse effects on people. "The Arctic 'polar vortex' (the persistent large-scale cyclone within which the ozone loss takes place) does not remain stationary over the pole," noted Manney, "but often shifts to lower latitudes, sometimes over densely populated regions." Protection from UV could therefore be severely diminished over northern European countries.
Manney added that because Arctic temperatures vary greatly from year to year, our ability to predict those variations is limited. "The unusually cold period in 2011 was not predicted in advance and we cannot say when such a lingering cold period might occur again in the Arctic."
The unusual ozone levels likely exposed the Arctic surface to unusually high levels of UV light during spring and early summer, according to co-author Andrew Klekociuk, senior scientist in the Australian Antarctic Division, which could have repercussions for the Arctic climate and ecosystems. "This event tests the ability of state-of-the-art climate models to simulate the observed conditions, and it's likely that we'll see improved understanding of the complex interplay between the chemistry and dynamics of the atmosphere as a result as scientists conduct further investigations," he said.
