- Extreme cold temperatures
- Man-made chemicals
- A stagnant atmosphere
"You can safely say that 2011 was very atypical: In over 30 years of satellite records, we hadn't seen any time where it was this cold for this long," says Susan E. Strahan, atmospheric scientist at NASA Goddard Space Flight Center and lead author of the new paper in the Journal of Geophysical Research-Atmospheres. "Arctic ozone levels were possibly the lowest ever recorded."
The NASA/Goddard animation shows the dynamics of ozone from January 1 to March 23 in 2010 and 2011.
But can we really be so confident about the unlikelihood of a repeat forecast, since so much of what's happening in the Arctic now is anomalous?