A new method for describing long-term changes in total ozone

A new method for describing long-term changes in total ozone was developed so that variations on time scales greater than that of the QBO may be examined. The technique fits a flexible tendency curve to total ozone data after explained variations have been removed. The derivative of the tendency curve is the growth rate curve. The average along this curve is comparable to total ozone trends reported in the past. Statistical uncertainty of the growth rate is determined using bootstrap techniques. Dobson column ozone measurements with long-term (30+ years) records from the NOAA/CMDL Cooperative Dobson Network were analyzed. Total ozone decreases ranged from 1-2%/decade since the 1960s and from 2-4%/decade since 1979 at all sites except Mauna Loa where results were not significant. The tendency curves indicate that the total ozone decline began in the 1970s and that there are no clear signs of recovery as of the end of 2000.