by Andrew Masterson
The 2018 hole in the ozone layer
was three times larger than
continental United States,
but it could have been worse.
NASA Goddard Space Flight Centre
size is testament
to success in
phasing out aerosols...
Despite extremely cold temperatures that ramped up the formation of
clouds containing ozone-destroying forms of
annual hole in
the ozone layer above the Antarctic was still smaller
in 2018 than it would have been 20 years ago.
The hole, which peaks every year at the end of the southern winter,
topped out at about 22.9 million square kilometers - almost three
times the area of the continental US - and was the thirteenth
largest out of the past 40.
And while that's not exactly cause for unrestrained celebration, it
is, say scientists at NASA's Goddard Space Flight Centre (GSFC) in
Maryland, which monitors the phenomenon, testament to the tentative
success of the
1987 Montreal Protocol, which led
to the phasing out of man-made ozone-depleting substances.
"Chlorine levels in
the Antarctic stratosphere have fallen about 11% from the peak
year in 2000.
"This year's colder temperatures would have given us a much
larger ozone hole if chlorine was still at levels we saw back in
the year 2000."
The size of the ozone
hole is directly affected by annual temperatures, with warmer
weather restricting its growth.
Warm averages in 2016 led
to a hole 19.7 million kilometers in area, but it increased in 2018
on the back of
the coldest run of temperatures since 1979.
Despite that, however, the relative size of the hole still
constituted cause for, well, at least two cheers.
"Even with this
year's optimum conditions, ozone loss was less severe in the
upper altitude layers, which is what we would expect given the
declining chlorine concentrations we're seeing in the
stratosphere," Bryan Johnson from the US National Oceanic and
Atmospheric Administration explains.