The polar atmosphere: ozone hole and polar vortex

Updated November 2026

Each southern spring, a large area of thin ozone opens high above Antarctica. It formed because of human-made chemicals, and it is slowly healing because nearly every country agreed to ban them. The same cold, spinning winds that help create the ozone hole, the polar vortex, also shape winter weather in the north.

What the ozone hole is

Ozone in the stratosphere, the layer of air above the weather, absorbs harmful ultraviolet light from the Sun. The “ozone hole” is not a place with no ozone at all. NASA defines it as the area where total ozone falls to 220 Dobson units or lower, a level never seen over Antarctica in measurements before 1979.

Why it forms over Antarctica

NASA explains the cause in steps:

  1. Chemicals rise. Human-made chlorofluorocarbons (CFCs) last for years in the lower air and slowly drift up into the stratosphere.
  2. Sunlight breaks them apart. Ultraviolet light frees chlorine, but most of it gets locked in harmless “reservoir” chemicals.
  3. The polar vortex isolates the air. In the dark Antarctic winter, a ring of strong winds traps very cold air over the continent. Polar stratospheric clouds form, and reactions on their particles turn the reservoir chemicals into chlorine gas.
  4. Spring sunlight starts the damage. When the Sun returns, it splits the chlorine gas. Each freed chlorine atom destroys ozone over and over, helped by bromine.

The hole grows from about August to October and fades as the vortex weakens and warmer air mixes in.

The Montreal Protocol

The Montreal Protocol on ozone-depleting substances was adopted on September 16, 1987. It is one of the rare treaties ratified by every country, and the World Meteorological Organization (WMO) calls it widely regarded as the most successful environmental treaty ever. In January 2023, the expert panel behind the 2022 scientific assessment for the treaty, published by WMO and the UN Environment Programme (UNEP), confirmed that nearly 99% of banned ozone-depleting substances had been phased out.

Recovery so far

The 2025 ozone hole was small and short-lived. Between September 7 and October 13, 2025 it averaged 18.7 million square kilometers, the fifth smallest since 1992, according to NASA and NOAA. Compare that with the record average of 26.6 million square kilometers in 2006: (26.6 − 18.7) ÷ 26.6 ≈ 0.30, so about 30% smaller. Its biggest single day came on September 9, 2025 at 22.9 million square kilometers, and it closed on December 1, 2025, the earliest since 2019 (Copernicus, reported by WMO).

Chemicals already in the air break down slowly. NOAA scientists say ozone-depleting substances in the Antarctic stratosphere have declined by about a third, measured against pre-ozone-hole levels, since they peaked around 2000. Year-to-year weather, especially how cold and strong the vortex is, also changes the size of each year’s hole.

When will the ozone layer be back?

If current policies stay in place, the 2022 assessment projects ozone returning to 1980 values (before the ozone hole appeared) by:

A new assessment was due in 2026, so check WMO or UNEP for updated dates.

The polar vortex

The Arctic has a polar vortex too. NOAA describes it as a band of strong westerly winds that forms each winter in the stratosphere, roughly 10 to 30 miles (16 to 48 km) above the North Pole. It is not the same as the polar jet stream, which blows lower down, about 5 to 9 miles (8 to 14 km) up, where weather happens.

Sudden warmings and cold snaps

Sometimes the vortex is disrupted and the polar stratosphere heats up sharply within days, an event called a sudden stratospheric warming. Research links these disruptions to outbreaks of extreme cold in the mid-latitudes of the United States or Eurasia, usually a few weeks later. Plenty of cold snaps also happen without any vortex involvement, so “polar vortex” in a weather headline does not always mean the stratosphere is to blame.

Is climate change weakening it?

Not clearly. A NOAA expert interviewed in 2021 said there was no convincing evidence of a long-term trend in the polar vortex, and climate models are split on whether warming will weaken or strengthen it. The IPCC gives medium confidence that Arctic sea ice changes could influence mid-latitude weather, but low confidence in detecting that effect for specific weather types.

Check yourself

Why does the ozone hole appear in spring and not in winter?

Winter cold and the polar vortex set the stage by turning chlorine into an active form on cloud particles, but the ozone-destroying reactions need sunlight. They start when the Sun returns in spring.

Why will the Antarctic ozone hole take until about 2066 to recover if CFCs are banned?

CFCs last for years in the atmosphere, so the chlorine already released is removed only slowly. Antarctica’s extreme cold also makes ozone loss there especially strong.

Is the polar vortex the same as the jet stream?

No. The polar vortex is in the stratosphere, about 10–30 miles up. The polar jet stream is lower, about 5–9 miles up, in the layer where weather happens.

Sources