Reevaluation of total-column ozone trends and of the Effective Radiative
Forcing of ozone-depleting substances
We evaluate total-column ozone trends using a piecewise linear
regression approach and maximizing usage of five gridded total-column
ozone datasets. The new approach yields more consistent estimates of
observed ozone loss during 1979-2000, when halocarbon concentrations
were increasing, and consequently, using CMIP6 simulations, an increased
Effective Radiative Forcing estimate of ozone-depleting substances with
a substantially reduced uncertainty range versus an earlier evaluation.
At more than 84% confidence it is now larger than zero and compares
more favorably with two previous evaluations. We furthermore find
significant, positive post-1997 global- and Southern-Hemisphere mean
trends, respectively, in these four datasets. For the extrapolar region
(60S-60N) and for the Northern Hemisphere, the assessment whether there
is a positive trend is inconclusive and depends on which observational
dataset is included in the calculation.