Last September 16 was celebrated the International Day for the Preservation of the Ozone Layer. In contrast to the ozone located in the leave part of the atmosphere (tropospheric ozone) -a dangerous pollutant we hear about every time a big city has pollution problems- the ozone located in the stratosphere (between 16 and 50 kilometers high) is of paramount importance for the development of life on the planet. In fact, although all the ozone in the stratosphere would be the size of a layer a few millimeters thick, its concentration is capable of eliminating 99% of the ultraviolet radiation coming from the sun, acting as a protective shield.

Although the effect of certain substances on stratospheric ozone had been known since the mid-1970s knowledge , the famous hole in the ozone layer was not discovered until 1985, when British researchers detected a large decrease in its concentration around the South Pole.

It then became known that substances widely used in industry, chlorofluorocarbon compounds (CFCs), were the main cause of their deterioration. In fact, these compounds - present in refrigerators, air conditioners or propellants (gases present in aerosols) - were considered almost perfect molecules due to their supposedly inert condition, which prevented them from reacting with other chemical elements. However, this virtue turned out to be their greatest drawback, since their leave reactivity allows them to remain in the atmosphere for decades and reach the stratosphere. There, due to the action of ultraviolet radiation, they release chlorine and bromine and trigger the ozone destruction process. Due to the special characteristics of the process - which cause the hole to be generated mainly in the polar areas (every year at the South Pole coinciding with the austral spring and, in particularly cold years, also at the North Pole) - the reduction of the layer is constant at a global level.

This generates well-known consequences (damage to the immune system, an incessant increase in cases of skin cancer...) and an exponential increase in the concern of the population and authorities around the world, which led to the Montreal Protocol protocol . The signature banned the use of CFCs and other compounds harmful to the ozone layer. In addition, it was the first multilateral environmental agreement that has achieved the participation of all countries, becoming an example of intense and loyal international partnership to solve a global problem.

Montreal was signed in 1987, only two years after the problem was uncovered. Today, thirty years after its entry into force entrance , the results are palpable. In fact, this year a NASA study has obtained for the first time direct evidence of the existence of a significant reduction in the levels of CFCs and, therefore, also of a decrease in the deterioration of the ozone layer. This has coincided with the information that, in 2017, the hole reached the smallest extent since 1988. Had it not been for the Montreal protocol , the damage would have been 40% greater.

Despite the positive news, and the indisputable improvement of the Antarctic hole, the reality is that the ozone layer is still being depleted globally and this is no longer linked to the concentration of CFCs, but to climate change. This finding confirms that its full recovery -as well as a large issue of environmental problems-, must go hand in hand with the mitigation of climate change: one of the greatest political, economic and social challenges humanity has ever faced.

In a recent lecture at the University of Navarra to position by Professor Mario Molina (winner of the award Nobel Prize for his research on the destruction of stratospheric ozone), this expert estimated the solution to climate change at only 1 or 2% of the world's GDP, and he cited the protocol of Montreal, precisely, as an example to follow.

For the moment, governments seem to be dragging their feet when it comes to addressing the enormous challenges of climate change. Once again, it will have to be society that pushes them to take the necessary measures to preserve the future of the next generations. Our future depends on it.