Antarctic ozone depletion influences rainfall in tropics

Danum Valley rainforest in Malaysia. CIFOR/Greg Girard
Monica Evans
15 September 2018

BONN, Germany (Landscape News) — For residents of New Zealand, Australia, Chile, Argentina or South Africa, the hole in the ozone layer that opens above Antarctica every spring is more than an abstract concern. The sun’s light burns more intensely through the hole increasing the risk of skin damage.

For people in places further away, although the ozone layer protects all life on earth, its depletion might not be so immediately apparent. But a new study led by researchers at Switzerland’s University of Bern shows that the depletion of the ozone layer, which blocks most of the ultraviolet radiation from the sun, has had previously unknown impacts on the climate system. Specifically, they’ve found that rainfall in tropical parts of the Pacific is influenced by the ozone hole – despite being 10,000 kilometers away.

The researchers ran simulations and statistical analyses on data from 1961 to 1996. The research revealed that the ozone hole causes a ridge to the east of New Zealand, which creates an atmospheric circulation pattern that alters the shape and position of the South Pacific Convergence Zone (SPCZ).

The SPCZ generally stretches from the equatorial western Pacific south-eastward toward French Polynesia, and is the most important rain belt in the Southern Hemisphere. The new circulation pattern has prompted an increase in rainfall on the northern flank of the zone, and a decrease on its southern edge.

The impacts on the ground are considerable: in Rikitea, French Polynesia, for example, average annual rainfall between October and December increased by 50 percent from the 1960s to the 1990s. These changes could well have societal impacts for the Pacific Island countries in and around the SPCZ, particularly for agriculture.

According to the study, as the ozone hole recovers over the next few decades, rainfall in the region is predicted to return to its original pattern, although climate change will also impact the area in ways yet to be seen.

“The fact that there are such connections in the climate system between places so far apart is fascinating,” said lead author and climatologist Stefan Brönnimann. “However, it is disturbing that people are responsible for this”, he added.

GLOBAL PACTS

On World Ozone Day on Sept. 16, this work provides a timely reminder that human activities have far-reaching consequences. The production and use of ozone-depleting substances – mostly on the other side of the world – has measurably impacted the climate of these extremely-isolated islands in the middle of the Pacific Ocean.

“When science showed us that chlorofluorocarbons (CFCs) and other substances were tearing a hole in the ozone layer that protects all life on earth, the world responded with determination and foresight by banning them,” said U.N. Secretary General António Guterres in a statement. “Thanks to this global commitment, the ozone layer is expected to return to its 1980 levels by mid-century.”

Under the Montreal Protocol, countries committed to banning chlorofluorocarbons and other substances that were creating the hole in the ozone layer. The ozone layer is now expected to return to its 1980 levels by mid-century, Guterres said.

The Kigali Amendment, which enters into force in January 2019 ratified by 46 countries, takes aim at hydrofluorocarbons, which are climate-warming gases still used in cooling systems.

“For over three decades, the Montreal Protocol has done much more than shrink the ozone hole; it has shown us how environmental governance can respond to science, and how countries can come together to address a shared vulnerability,” Guterres said.

“I call for that same spirit of common cause and, especially, greater leadership as we strive to implement the Paris Agreement on climate change and mobilize the ambitious climate action we so urgently need at this time.”

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