Global iodine levels set to reach record high by 2050, threaten ozone layer

Iodine is well-documented in its ability to destroy ozone. Until recently, it was regarded as a useful tool to weaken the ozone closest to the earth's surface (tropospheric ozone), which is a key component of smog. The problem is that what goes on in the troposphere doesn't stay in the troposphere, which means some of this iodine escapes up to the 'good' ozone (stratospheric ozone, which forms the ozone layer). A 2020 experiment at the University of Colorado Boulder showed that iodine processes could account for over 30% of the ozone loss in the lower stratosphere. Iodine also increases the lifetime of greenhouse gases like methane by gobbling up the free radicals that would have otherwise absorbed them.

Antarctic springtime (Sep-Nov) ozone levels decrease by up to 11% with the addition of iodine

Simulated average Antarctic ozone levels in parts per billion, 1980-2015

Source: The influence of iodine on the Antarctic stratospheric ozone hole

Even as the ozone layer shows signs of recovery in the upper stratosphere, ozone in the lower stratosphere continues to decline. This is despite the success of the 2016 Montreal Protocol – iodine levels were so low at the time that they were not considered for regulation. Scientists at the Spanish National Research Council (CSIC) now believe that iodine emissions are one of the largest contributors to atmospheric ozone depletion.

The main sources of iodine are marine life and human emissions. NASA has found that Arctic sea ice extent has been shrinking by 12.6% every ten years since 1979. With this increased sea surface area, the number of underwater plankton and algae that emit organic iodine had been increasing as well. And when large waves break on the shore? Sea sprays are hotbeds for this iodine to be released into the atmosphere.

A 2022 study at CSIC identified two key measurements that preceded the highest-ever iodine levels 130,000 years ago:

1. The northern Atlantic Ocean had a surface temperature of 16°C.
   That is only 2°C greater than its average temperature in 2022, and it is projected to rise by 3-4°C by 2100.


2. The Arctic region had "almost ice-free summers".
   The European Space Agency predicts ice-free Arctic summers by 2050.

On top of that, non-oceanic (inorganic) iodine levels were negligible 130,000 years ago. Inorganic iodine now accounts for approximately 75% of the total iodine in the atmosphere due to the significant rise in human emissions. Left unmitigated, the planet's iodine levels could soon surpass all recorded measurements.