Calcutta, Nov. 26: Earth can breathe easier. An ongoing global effort to save the shield that filters out harmful levels of ultraviolet rays from the sun has been dubbed an “outstanding success” story.

The Montreal Protocol, a two-decade old international treaty to protect the ozone layer, has achieved significant reduction of ozone-depleting substances (ODSs), according to a report released today by the United Nations Environment Programme.

The report — HFCs: a critical link in protecting climate and the ozone layer — said the treaty had resulted in “one of the largest reductions to date in global greenhouse gas emissions”.

The expected outcome: possible reduction in global warming, the agent of climatic change that could wreak havoc in the long run.

“Since most ODSs are also potent greenhouse gases, actions under the Montreal Protocol have had the very positive side effect of substantially reducing a main source of global warming” the report, a copy of which is with The Telegraph, said.

The report said the “phasing out of ODSs” had between 1988 and 2010 “led to a drop of about 8.0 gigatonnes equivalent (of) carbon dioxide emissions” per year.

In 2010 alone, the reduction was 10 gigatonnes.

The cut is significant as one gigatonne of carbon dioxide — or one billion tonne — is said to have significant global warming potential.

According to the Intergovernmental Panel on Climate Change, the annual global CO2 emission has to be reduced from about 28 gigatonnes in 2006 to 20 gigatonnes by 2050 and to 10 gigatonnes by 2100 if the world is to remain habitable.

The report said the “avoided annual emissions of ODSs is about five times greater than the annual emissions reduction target for the first commitment period (2008-2012) of the Kyoto protocol”.

The authors of the report hailed the Montreal Protocol as “one of the truly outstanding success stories of international cooperation on sustainable development” since the treaty came into force on January 1, 1989. India signed the treaty in 1992.

The trigger for the protocol was the discovery of a major ozone hole near Antarctic in the mid-eighties. Since the ozone layer screens harmful levels of ultra-violet rays, the fear was depletion in the level could lead to an increase in health problems, including skin cancers.

It was believed that if the 196 signatory countries kept their commitment, the thinned-out ozone layer could recover by 2050. But the actual progress has been found to be much quicker.

Under the treaty, substances believed to be responsible for ozone depletion — Chlorofluorocarbon and its derivatives, mostly used in refrigeration — were identified and a timetable was set to replace them internationally.

“Since the 1980s, nations have worked together to phase out the chemicals that have been damaging and degrading the ozone layer. More recently, science has spotlighted that this international effort has also spared humanity a significant level of climate change,” the authors of the report said.

The report has, however, cautioned that the concentration of hydrofluorocarbons (HFCs), which replaced ozone-depleting substances and are currently found in very low concentrations in the atmosphere, was on the rise. “Without intervention, the increase in HFC emissions is projected to offset much of the climate benefit achieved by the earlier reduction in ODS emissions,” the report said.

Many experts claimed the success had come by default. “Although a regulation to limit ODS and industry acceptance was important, one cannot count out the role of the global financial meltdown and negative growth of manufacturing industries to this significant reduction,” said professor Siddhartha Datta, an environment expert from Jadavpur University.

“The fact that the ozone holes happened closer to the poles and, hence, developed countries contributed to its (the protocol’s) serious implementation and success,” said Dipak Chakrabarty, a former chief scientist of the Bengal pollution control board.