the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery
Justin Alsing
Daniel J. Mortlock
Johannes Staehelin
Joanna D. Haigh
Thomas Peter
Fiona Tummon
Rene Stübi
Andrea Stenke
John Anderson
Adam Bourassa
Sean M. Davis
Doug Degenstein
Stacey Frith
Lucien Froidevaux
Chris Roth
Viktoria Sofieva
Jeannette Wild
Pengfei Yu
Jerald R. Ziemke
Eugene V. Rozanov
Abstract. Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective ozone layer
around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60° S and 60° N outside the polar regions (60–90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60° S and 60° N. We find that total column ozone between 60° S and 60° N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established.
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