NASA announced Tuesday that the ozone hole is the smallest its ever been since its discovery. Reason being? Abnormally warm temperatures in the stratosphere.
‘Good’ vs. ‘bad’ ozone
The ozone layer is found 7-25 miles above the earth in the stratosphere. Ozone in the stratosphere is known as the “good ozone” as it help blocks harmful ultra-violet radiation that causes skin cancer and cataracts. Ozone created by vehicle exhaust and industrial emissions at the surface is known as ‘bad ozone’ and is detrimental to human health
Discovery of the ‘ozone hole’
In the 1970s, scientists observed the dramatic thinning in Earth’s protective ozone layer, known as the “ozone hole” over the Antarctic. They determined the production of chlorofluorocarbons (CFCs) found in refrigerators and aerosol sprays caused the problem. In the late 1980s, countries across the globe came together to sign the Montreal Protocol, a treaty designed to protect the ‘good ozone’ by phasing out the production of harmful agents known to deplete it.
Unusual stratospheric weather in 2019
Using instruments called ‘ozonesondes’ (similar to the instruments attached to weather balloons), scientists are able to measure the pressure, temperature, humidity and thickness of ozone.
This year, the measured temperature at 12 miles above the surface was 29°F warmer than normal, the warmest in the 40-year historical record for September.
The ozone hole typically reaches it’s minimum in Southern Hemisphere spring (Sept/Oct) as ozone depletion is lessened with warmer temperatures.
According to NASA and NOAA satellite measurements, the ozone hole reached its annual peak of 6.3 million square miles on September 8th, then shrank to less than 3.9 million square miles for the remainder of September and October. Under normal weather conditions, the peak is near 8 million square miles in late September or early October.
The reason for shrinking
The reason for the warming is complex… but is focused on the changes in the Antarctic polar vortex. The atypical stratospheric weather led to a shift in the polar vortex position and reduction of wind speed in the jet stream, dropping from 161MPH to 67MPH. The slower winds allowed for sinking air, limiting the development of stratospheric clouds while also pulling in ozone from higher latitudes over the ozone hole. Both processes led to an increase in ozone levels over Antarctica (smaller ‘ozone hole’).
Has this happened before?
This is the third time in 40 years that unusually warm temperatures in the stratosphere have limited ozone thinning, the other two in 1988 and 2002. Since the ban of harmful ozone-depleting chemicals in the late 1980s, the ozone hole has made small progress towards recovery… however, scientists do not expect to get back to 1980 level’s until the year 2070.
The good news
According to chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center, Paul Newman, “It’s great news for ozone in the Southern Hemisphere… but it’s important to recognize that what we’re seeing this year is due to warmer stratospheric temperatures. It’s not a sign that atmospheric ozone is suddenly on a fast track to recovery.”
It’s also important to note that there is no identified link between the warmer than normal temperatures in the stratosphere and climate change. Scientists say the unusual warming is a rare and there is still a lot unknown about these types of events.
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