Impact of the Montreal Protocol: Evidence from Stratospheric Ozone Data

The manufacture and release of chlorofluorocarbons (CFCs) during the 1970s and 1980s led to an increasing stratospheric abundance of chlorine compounds that can catalytically destroy ozone. The Montreal Protocol is an international agreement that has limited the source of chlorine compounds to the stratosphere. The fluorocarbon-ozone theory predicts that stratospheric ozone is affected by CFCs. Ozone measurements from the series of SBUV instruments on NASA and NOAA satellites form a continuous data set from late 1978 to the present. I will show time series of these data that illustrate the long-term behavior of ozone in the stratosphere. I will place particular importance on the uncertainties involved in constructing a time series from multiple satellite instruments. The instrumental uncertainties can be characterized by estimating potential calibration offsets and instrument drifts. We detect clear signals of ozone decrease during the 1970s and 1980s. There is no further decrease since the late 1990s. The data is consistent with a small increase in ozone over the last decade as would be expected from the implementation of the Montreal Protocol. It will require about another decade of data to allow a definitive attribution of increases to the effects of the Protocol.