"World Avoided" model charts climate cost if we'd ignored ozone hole
It’s easy to feel hopeless in the face of climate change, but it’s not too late to do something about it – after all, we’ve stepped up to similar challenges before. New modeling shows just how much worse the situation would be if CFCs hadn’t been banned decades ago, with the ozone hole growing, raising temperatures and interrupting the ability of plants to sequester carbon.
The ozone layer is an important part of the Earth’s atmosphere, absorbing the majority of the ultraviolet radiation from the Sun. But in the late 1970s, it was found that commonly used compounds called chloroflurocarbons (CFCs) were depleting this protective layer, and in 1985 scientists discovered a large seasonal ozone hole above Antarctica.
Soon after, 197 United Nations countries signed the Montreal Protocol into effect, which banned the use of CFCs. And it worked – 30 years later, the ozone hole is steadily closing. So how much damage did we really avoid? Plenty of research has modeled how much warmer the world might have become if CFC use hadn’t been curbed, but a new study highlights a factor that may have been previously overlooked.
Within Earth’s carbon cycle, there are a few natural “sinks” that capture and store carbon, reducing the amount of carbon dioxide in the atmosphere. Plants, particularly forests, are major carbon sinks, but this ability would have been disrupted by the extra UV light an ozone hole would let through. So for the new study, the researchers developed a new model that incorporated this factor.
The team modeled a "World Avoided" where CFC use continued to grow by three percent per year – a conservative estimate – and calculated what effect that would have on ozone depletion, how much extra UV that would let in, how much damage that could cause to plants, how that would affect their carbon uptake and, ultimately, what this altered carbon cycle would contribute to climate change.
The model suggested that the ozone layer would have essentially collapsed by the 2040s, and by 2050 UV exposure in the mid-latitude regions would be stronger than it currently is at the tropics. The mid-latitudes, for reference, encompass all of the contiguous United States, the vast majority of Europe, much of Asia, and the southern areas of South America and Australia. The tropics would fare badly, too, seeing ozone levels drop by 60 percent by the end of the century.
That boosted UV radiation would increase health problems in humans, animals and plants alike. As such, the team estimates that up to 580 billion tonnes less carbon stored in vegetation and soil, leaving 40 to 50 percent more carbon dioxide in the atmosphere – between 165 and 215 parts per million (ppm). That in turn would have added an extra 0.8 °C (1.4 °F) of warming, through the greenhouse effect.
It doesn’t end there, though. CFCs are themselves a greenhouse gas, and having more of them in the atmosphere would directly boost temperatures by as much as 1.7 °C (3 °F). That would bring the total warming under this scenario to a huge 2.5 °C (4.5 °F).
“We show in this work that reducing ozone-depleting substances, through the Montreal Protocol, had the added benefit of protecting the world’s vegetation and avoiding a catastrophic collapse of forests and croplands by the middle of the century,” says Dr. Anna Harper, an author on the study. “The loss of carbon stored in plants and soils in our ‘world avoided’ scenario by 2100 would be roughly equivalent to 50 to 60 years worth of emissions at our current rates of fossil fuel burning and deforestation.”
This kind of work is important to keep in mind, as a reminder that mitigation processes have worked in the past, and, importantly, can work in the future. There is still time to avoid the worst effects of climate change, but it will require a lot of work and that time is running out.
The research was published in the journal Nature.
Source: University of Exeter