As the UN climate summit in Copenhagen approaches, we must remember that 50% of climate change is caused by gases and pollutants other than CO2
Achim Steiner, guardian.co.uk 11 Sep 09;
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 ultraviolet 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 tenfold by 2050. This could have led to up to 20m additional cases of skin cancer and 130m 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 (16 September). 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 it prohibits also contribute to global warming.
Indeed, a study in 2007 calculated the climate mitigation benefits of the ozone treaty as totalling the equivalent of 135bn tonnes of C02 since 1990, or a delay in global warming of seven-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 remains about some of these pollutants' precise contribution to warming. 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 ecosystems, including forests.
Consider black carbon. A component of the soot emissions from diesel engines and the inefficient burning of biomass cooking stoves, it is linked to 1.6m-1.8 million premature deaths annually as a result of indoor exposure and 800,000 from outdoor exposure. Black carbon, which absorbs heat from the sun, also accounts for anywhere from 10% to 45% of the contribution to global warming, and is linked to accelerated losses of glaciers in Asia, because the soot deposits darken ice and make it more vulnerable to melting.
One study estimates 26% of black carbon emissions come 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 use passive air flows, better insulation and 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 short periods – days, weeks, months or years – so that reducing or ending emissions promises almost immediate climate benefits.
The international community's overarching concern must be to seal a serious and significant deal at the UN climate summit in Copenhagen in December to curtail CO2 emissions and assist vulnerable countries to adapt. If the world also is to deploy all available means to combat climate change, emissions of all the substances that contribute to it must be scientifically evaluated and urgently addressed.
• Achim Steiner is UN under-secretary general and executive director of the UN Environment Program.
