The weakening of the ozone layer, which protects the earth from ultraviolet radiation from the sun, has stopped and ozone levels have started to rise.
A Finnish and American group of researchers has examined a series of measurements taken by two satellite measuring instruments. With the help of the instruments on the GOMOS and SAGE II satellites, a combined series of measurements over 27 years has been created. The measurements indicate that a change took place in about 1997. The year is the same when the levels of substances that destroy ozone reached their peak in the ozone layer and started to decline.
"By using complex atmospheric models it is possible to predict that the ozone layer will recover by mid-century", says Research Professor Erkki Kyrölä of the Finnish Meteorological Institute.
This positive development indicates that the international Montreal Protocol signed in 1988, which banned the use of CFC gases which destroy ozone, has been effective.
Climate change also affects the recovery of ozone. Climate change speeds up the recovery of ozone in all areas except the polar regions, where the cooling of the upper atmosphere might accelerate the formation of polar stratospheric clouds, which destroy ozone.
SAGE II is an American satellite instrument, which measured ozone levels from 1984-2005 by using solar radiation. This series of measurements has often been called the gold standard of ozone because of the high quality of the data. GOMOS, which measures radiation from the stars, measured ¬about a million vertical measurements of ozone between 2002 and 2012. The Finnish Meteorological Institute has GOMOS measuring instruments on the Envisat satellite of the European Space Agency. Envisat and GOMOS shut down in April last year for reasons that remain unknown. The Finnish Meteorological Institute continues to take part in the measurement activities of two satellite measurement devices, OMI and OSIRIS.
Research Professor Erkki Kyrölä, Tel. +358 50 339 7041, email@example.com