Free Astronomy Magazine January-February 2018

42 JANUARY-FEBRUARY 2018 SPACE CHRONICLES Ozone ups and downs by ESA C limate scientists studying three decades of ozone measure- ments from seven satellites see a positive trend in global recov- ery thanks to international efforts to curb ozone-depleting substances. The part of Earth’s atmosphere with high concentrations of ozone gas protects life on Earth from the Sun’s ultraviolet radiation. However, pol- lutants can break down ozone, thin- ning this layer and creating the infamous ozone hole. The depletion of ozone in our atmo- sphere and subsequent increase in ultraviolet exposure causes skin can- cer, cataracts and immune system damage in humans, and injures ani- N egative ozone trends in the upper strato- sphere before 1997 and positive trends after 1997 are observed. Shaded areas show regions where the trends are statistically significant. [FMI] T he ozone layer protects life on Earth from ultraviolet radiation but it is also a powerful greenhouse gas. Satellites can provide measure- ments of atmospheric ozone and monitor distribution changes with the seasons. [Planetary Visions (credit: ESA/CCI Ozone and Aerosol teams/Planetary Visions)] mals, plants and even mi- croscopic phytoplankton. Starting in the 1970s, ozone in the stratosphere – some 11–50 km above Earth’s surface – began to decline worldwide. The largest drop was in the upper stratosphere, at 4– 8% per decade. The trend was interrup- ted following interna- tional agreements on the reduction of ozone-depleting substances and the first signs of ozone recovery were seen by satellites. Satellites provide good coverage but operate for a limited number of years. Meanwhile, climate scientists re-