- The calculations of the recovery of the ozone layer are based on models.

But the connections are complicated and no model is infallible, says Johan Mellqvist, professor of optical remote sensing at Chalmers University of Technology, where the middle atmosphere and its trends have long been researched and measured.

Since 1994, he also oversees the special measurements that are made at Harestua north of Oslo and at around 15 locations on Earth.

Here, not only the ozone layer is measured, but also various chemical substances that break down the ozone, above all chlorine.

Several clouds of worry

Concern clouds are the large releases of nitrous oxide in, for example, agriculture that damage the ozone layer, and other events that make forecasts uncertain;

such as strong volcanic eruptions and extensive forest fires, which can also damage the ozone layer.

There has also been deterioration in parts of the layer in recent years.

For example, the ozone hole over Antarctica that scientists raised the alarm about in the 1980s has been larger in several of the last few years than ever before.

Slow recovery

According to the model used by the UN scientific panel, the recovery of the ozone layer will only take place around 2066 and the values ​​will not be clearly better until a number of years from now.

But until it is seen that things are turning around and the model is correct, Johan Mellqvist believes that it is too early to shout hello.

- Our measurements simply show no recovery of the ozone layer and it is not time to sit back, he says.

"Need for good news"

The agreement from Montreal in 1987, when the countries of the world agreed to regulate ozone-destroying chemicals, is highlighted today as a great success - both for ozone and for international cooperation in general.

It is also used as a reminder in the ongoing climate negotiations.

Not least in connection with demands to phase out the use of fossil fuels - that we have actually succeeded in phasing out dangerous substances in the past.

- I think there is a need for positive news in this context, but the UN panel tends to claim victory in advance and this can have serious effects.

Important satellite measurements of ozone are already being phased out, even though we are not there yet.

We must continue to monitor this closely for many decades to come, says Johan Mellqvist.