December 2, 2023


The Montreal Protocol does not only protect the ozone layer

In 1987, the Montreal Protocol banned the emission of ozone-depleting propellants, and the Earth’s ozone layer has since recovered. But as simulations now show, the protocol could have saved us from even worse climate change. Had humanity continued to emit ozone-depleting substances unchecked, the greenhouse effect of these gases alone would have warmed the climate by an additional 1.7 degrees by 2100. Plus, another 0.8 degrees, because vegetation would have absorbed less CO2 Carbon (CO2) due to increased exposure to UV rays. Carbon dioxide values ​​will be about 30 percent higher by 2100 and that warming will increase by an additional 2.5 degrees, the researchers determined.

Earth’s ozone layer is our most important protection against harmful UV rays. If the high-energy short wave radiation hits the ozone molecule, it splits it and is absorbed in the process. In this way, the ozone layer protects humans, animals and plants from cells and genetic damage caused by excessive exposure to ultraviolet rays. We owe the fact that the ozone layer is still largely intact today to the Montreal Protocol adopted in 1987. At that time, chlorofluorocarbons (CFCs) and other halogen-containing fuels were recognized as having a destructive effect on the ozone and are responsible for the formation of the ozone hole. over Antarctica. Therefore, with the Montreal Protocol, the international community banned the production and emissions of a large number of these ozone-depleting substances. As a result, the ozone layer has since partially recovered, but the longevity of some CFCs means that ozone density has diminished to this day—even above northern latitudes.

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But if the Montreal Protocol did not exist, the ozone situation would look much worse today, as some time ago the so-called “avoid the world” simulation appeared. For them, scientists use geophysical data and atmospheric models to reconstruct how the ozone layer, climate, and UV exposure would develop if CFC emissions continued after 1987. Such scenarios show, among other things, that UV exposure at latitudes We have it increased by 15 percent and that there will also be a regular ozone hole over the North Pole. In addition, there is another effect of halogenated hydrocarbons: they are powerful greenhouse gases, the effect of which is sometimes thousands of times stronger than that of carbon dioxide. So the ban on these substances had a climatic impact.

Focus on the climate impact of the Montreal Protocol

Paul Young of Lancaster University and colleagues have now investigated exactly what this effect will look like and how the global climate and atmosphere could evolve by 2100 without the Montreal Protocol. The first focus was on an aspect not taken into account in previous World Avoided studies: the effect of significantly increased UV exposure on vegetation. “Experimental data indicate that uncontrolled ozone depletion, and in particular increased UV-B radiation, has a significant negative effect on plant growth,” the researchers explained. This reduces the net primary production and thus also the amount of carbon dioxide that the plant absorbs and stores as part of photosynthesis. As a result, the insulating effect of plants, which until now absorbs part of the carbon dioxide emissions and reduces their climatic impact, is reduced.

For their model scenarios, Young and his team simulated vegetation evolution, CO2 values, and temperatures up to 2100 based on a CFC ban and rather weak climate protection with only a reduction in CO2 emissions from 2075. Scenario Two – Fixed1960 -Based on climate protection offset, but in a world without the Montreal Protocol, where CFC production and emissions continued into the 1960s. As a third, they simulated “avoid the world” as a worst-case scenario, with FKCW emissions increasing three percent per year. As expected, this scenario will gradually deplete the ozone layer. “This thinning will accelerate in the 1940s, when the ozone layer collapses worldwide,” the researchers wrote. “By 2100, the global average ozone density will fall to 90 Dobson units, which is a 72 percent reduction compared to the control scenario with the Montreal Protocol.”

Extra warming 2.5 degrees

The impact of greenhouse gas fertilization and ozone depletion on the climate would be significant: with the Montreal Protocol, simulations predicted a 2100 increase in global temperatures of 3.2 degrees above average between 1986 and 2005. The additional greenhouse effect of CFCs alone would That “avoid the world” would add another warming of 1.7 degrees – the effect on vegetation not yet taken into account here. If you add this, the scenario gets darker. “Increasing exposure to UV rays would drastically reduce the plant’s ability to absorb carbon dioxide, leading to higher CO2 values ​​and increased global warming,” explains Young. By absorbing a three percent reduction in uptake for every 10 percent additional UV exposure, vegetation would reduce about 580 billion tons (gigatons) of carbon by the end of the century. As a result, the CO2 content in the Earth’s atmosphere would be 165 to 215 parts per million (ppm) CO2 higher than it was in the ban scenario – this corresponds to about 30 percent more. For the climate, this means another 0.8 degree warming.

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Overall, the Montreal Protocol and the subsequent ban on ozone-depleting substances saved the world from a hot period in two ways: avoiding the greenhouse effect of CFCs would have warmed the climate by an additional 1.7 gad, and the buffering effect from vegetation, which was from Possible to decrease due to UV damage by another 0.8 degrees. In the “avoid the world” scenario, we would therefore have to account for a 2.5 degree increase in temperature from the weak ozone layer and CFCs alone. This would add to the three degrees of warming already expected due to our CO2 emissions on top of that. “Our research shows that the success of the Montreal Protocol goes beyond protecting the human race from increased exposure to UV radiation – it also preserves the plant world’s ability to absorb carbon dioxide,” Young says. “Of course we hope our worst doesn’t happen, but it reminds us once again of the importance of protecting the Earth’s ozone layer.”

Quelle: Paul Young (Lancaster University, UK) et al, Nature, doi: 10.1038/s41586-021-03737-3