Twenty years ago, governments adopted the Montreal Protocol, a treaty to protect the Earth’s ozone layer from emissions of destructive chemicals. Few could have foreseen how far-reaching that decision would prove to be.
The Protocol explicitly aimed at phasing-out substances such as chlorofluorocarbons (CFCs) – found in products such as refrigerators, foams, and hairsprays – in order to repair the thin gassy-shield that filters out the sun’s harmful, ultra-violet rays.

By 2010, close to 100 ozone-depleting substances, including CFCs, will have been phased-out globally.
Without the decisions taken 20 years ago, atmospheric levels of ozone-depleting substances would have increased ten-fold by 2050.

This could have led to up to 20 million additional cases of skin cancer and 130 million more cases of eye cataracts, not to speak of damage to human immune systems, wildlife, and agriculture.

But this is only part of the story that we celebrate on the International Day for the Preservation of the Ozone Layer (September 16).

Over the past two years, it has been established that the Montreal Protocol has also spared humanity a significant level of climate change, because the gases that it prohibits also contribute to global warming.

Indeed, a study in 2007 calculated the climate mitigation benefits of the ozone treaty as totaling the equivalent of 135 billion tons of C02 since 1990, or a delay in global warming of 7-12 years.

So the lessons learned from the Montreal Protocol may have wider significance.

Scientists now estimate that somewhere close to 50% of climate change is being caused by gases and pollutants other than C02, including nitrogen compounds, low-level ozone formed by pollution, and black carbon.

Of course, a degree of scientific uncertainty about some of these pollutants’ precise contribution to warming remains. But they certainly play a significant role.

Meanwhile, many of these gases need to be curbed because of their wider environmental impact on public health, agriculture, and the planet’s multi-trillion dollar ecosystems, including forests.

Consider black carbon, a component of the soot emissions from diesel engines and the inefficient burning of biomass cooking stoves that is linked to 1.6 million to 1.8 million premature deaths annually as a result of indoor exposure and 800,000 as a result of outdoor exposure.

Black carbon, which absorbs heat from the sun, also accounts for anywhere from 10% to more than 45% of the contribution to global warming, and is also linked to accelerated losses of glaciers in Asia, because the soot deposits darken, ice making it more vulnerable to melting.

One study estimates that 26% of black carbon emissions are from stoves for heating and cooking, with more than 40% of this amount from wood burning, roughly 20% from coal, 19% from crop residues, and 10% from dung.

Some companies have developed stoves that using passive air flows, better insulation, and wh 60% less wood to reduce black carbon emissions by around 70%.

Mass introduction of such stoves could deliver multiple green-economy benefits.

While CO2 can remain in the atmosphere for centuries, other pollutants, including black carbon and ozone, remain for relatively periods – days, weeks, months, or years – so that reducing or ending emissions promises almost immediate climate benefits.

The international community’s over-arching concern must be to seal a serious and significant deal at the United Nations climate summit in Copenhagen in December to curtail C02 emissions and assist vulnerable countries to adapt.

If the world also is to deploy all available means to combat climate change, emissions of all substances that contribute to it must be scientifically evaluated and urgently addressed.

Achim Steiner is UN Under-Secretary General and UN Environment Program Executive Director.