🌍 The size of the hole in the ozone layer in 2025 is surprising and reassuring

The NOAA and NASA agencies have reported that the hole in the ozone layer above Antarctica is this year the fifth smallest since 1992. At its peak, it covered an average of 18.71 million square kilometers (about 7.22 million square miles), which is 30% smaller than its largest measured size in 2006. And its breakup began almost three weeks earlier than the average of the last ten years. These measurements are part of a downward trend observed for several decades, thanks to international efforts.

This reduction is largely attributed to the Montreal Protocol, which limited the use of ozone-depleting substances. Chlorine levels in the stratosphere have fallen by about one-third since the 2000s. Coordinated global actions have thus effectively curbed the degradation.

In addition to human actions, natural variations played a role. A weaker polar vortex this year maintained higher temperatures, limiting ozone loss. These meteorological factors partly explain the annual fluctuations, showing that local climate also influences the size of the hole. Scientists are closely monitoring these interactions to refine their forecasts.


The ozone layer acts as a shield against the Sun's ultraviolet rays. Its thinning exposes the Earth's surface to health and environmental risks, such as skin cancers and damage to crops. Chlorine and bromine compounds, once used in aerosols and refrigerants, are responsible for this degradation. Their persistence in the atmosphere requires continuous monitoring to protect ecosystems.

To track these changes, scientists use satellites like NASA's Aura and ground-based instruments. Weather balloons are regularly launched to measure ozone directly above the South Pole, providing precise data on its state in Dobson units (explanation at the end of the article). This combination of technologies allows for a comprehensive assessment of the evolution of the ozone layer on a global scale.

With the continued reduction of emissions, researchers predict that the Antarctic ozone hole could be restored by the 2060s. Each year brings data confirming this positive trend, offering hope for the restoration of this essential barrier. International collaboration remains key to maintaining these long-term gains.

Dobson units: understanding the measurement of ozone

Dobson units are a standard measurement used to quantify the amount of ozone in the atmosphere. They represent the thickness of the ozone layer if it were compressed to sea-level pressure. This unit, named after scientist Gordon Dobson, allows researchers to easily compare data across different periods and regions.

For example, a value of 220 Dobson units is often used as a threshold to define the 'hole' in the ozone layer. Below this level, protection against UV rays is significantly reduced, increasing risks to health and the environment. Measurements below this threshold indicate significant ozone degradation.

Scientists measure these units using instruments such as ozonesondes on weather balloons or satellites equipped with spectrometers. These tools collect precise data on ozone concentration at different altitudes, allowing for the mapping of its distribution. This information is crucial for assessing the effectiveness of protection policies.

Understanding these measurements helps track seasonal and long-term variations in ozone. They inform us about the state of the protective layer and guide decisions to maintain or improve its health. Dobson units are thus a fundamental tool in global environmental monitoring.