In recent years, scientists have put forward several geo-engineering schemes to cool the planet and mitigate the effects of global warming. One of the most popular, proposed by atmospheric chemist and Nobel Laureate Paul Crutzen, would be to regularly inject large amounts of sulphate particles into the stratosphere. These particles would block the Sun's rays and cool the Earth's surface, in the same way that major volcanic eruptions do.

"Our study shows that trying to artificially cool off the planet using global geo-engineering solutions might have dangerous side effects on our society and all life on Earth," team member Simone Tilmes told environmentalresearchweb. "Pumping large amounts of sulphur into the stratosphere can result in a much thinner ozone layer for several decades, especially in the Northern Hemisphere in winter and spring, and delay the recovery of the ozone hole that occurs each winter over Antarctica by 30 to 70 years."

Tilmes and co-workers analysed how the ozone layer thinned in the past as aerosol content in the atmosphere varied. This included the effect of major volcanic eruptions on ozone loss. The researchers then extrapolated these observations into the future. Although the sulphates from volcanoes do not directly destroy ozone, they provide a surface on which chlorine gases – from chlorofluorocarbons (CFCs), for example – can become activated to produce chemical reactions that do destroy it.

The team also looked at the effect of reduced amounts of CFCs in the atmosphere as a result of the ban on these chemicals by industrialized nations in the early 1990s (the Montreal Protocol). Finally, the researchers considered what impact large quantities of particles from geoengineering would have on ozone.

The conclusion is that injecting particles into the stratosphere over the next 20 years could temporarily reduce the ozone layer in winter and spring by as much as 100 to 230 Dobson units, depending on the size of the particles. Smaller particles cause greater ozone destruction. To get an idea of the severity, the average thickness of the ozone layer in the Northern Hemisphere is just 300 to 450 Dobson units.

Tilmes and colleagues say that actual ozone depletion could differ from these estimates if polar winters were unusually cold or warm. And more severe ozone loss could occur if a major volcanic eruption occurred at the same time as an injection experiment.

The ozone layer is important for life on Earth because it protects organisms from dangerous ultraviolet radiation emitted by the Sun, which can increase the incidence of various types of cancer.
"This work warns about one side effect from artificially cooling down the planet," continued Tilmes. "However, it is important to address this subject in more detail – our study is a projection of past atmospheric conditions into the future, but we did not include estimates of how a changing climate can affect atmospheric conditions. We also did not consider the effect of geo-engineering on ozone in lower latitudes."

More research is needed to understand if global geo-engineering can be accomplished safely, she added.

"We should not forget that, although geo-engineering might be considered in the future, the most important way to solve the problem of global warming is to reduce and eventually stop the consumption of fossil fuels," she said.

The work was reported in Sciencexpress.