Chris de Freitas: Our humble cows help make the world a cooler place

The findings come from experiments conducted in the Cloud (Cosmics Leaving Outdoor Droplets) chamber at Cern, known also as the Cern Proton Synchrotron. Photo / AP

A recent discovery that agricultural practices help form clouds could change the way we see New Zealand's environmental performance.

New Zealand's potential contribution to global warming is not typical of nations that signed up to the Kyoto Protocol aimed at cutting greenhouse gas emissions. We stand out because almost 50 per cent of our emissions come from the agricultural sector. By comparison, emissions from agriculture typically make up only about 12 per cent of total greenhouse gas emissions across Kyoto signatories.

New Zealand's agricultural contribution is predominantly emissions from ruminant farm animals. Paradoxically, new ground-breaking research shows this may actually work in New Zealand's favour when it comes to assessing our environmental performance.

A team of 79 scientists writing in the journal Nature this month address the puzzle of how up to half the clouds in the sky are formed. They found that humans play a significant role mainly through pastoral farming.

Clouds are by far one of the most important controls on global climate because they reflect back to space energy from the Sun that would otherwise heat Earth's atmosphere. An increase in global cloud cover of just 2 per cent corresponds to a global temperature decrease of about 0.12C.

The 79 scientists from the renowned Cern research laboratory in Switzerland show for the first time how gas vapours, mainly from animal husbandry, can react to create the essential tiny particles around which the condensation droplets that cause clouds form.

The findings come from experiments conducted in the Cloud (Cosmics Leaving Outdoor Droplets) chamber at Cern, known also as the Cern Proton Synchrotron. The research shows that gases called amines - from ammonia produced in large quantities as a result of farming cattle, sheep and other animals - can help form the seed particles necessary for cloud formation.

The process of nucleation of aerosol particles, referred to as amine ternary nucleation, was up until now poorly understood. The Cern experiments provide direct evidence for amine ternary nucleation under atmospheric conditions.

Aerosols can cause a net cooling of climate by scattering sunlight and by leading to more numerous cloud droplets, which makes clouds brighter - thus more reflective - and prolongs their lifetimes.

The lack of knowledge of the role of aerosols in cloud formation is well established as the major source of uncertainty in predictions about global warming. The fact that amines are produced by pastoral activity means that humans are responsible for a previously unknown global cooling effect. This may mean that, once greenhouse gases are taken into account, human-caused global warming may actually be less than thought.

What all this means for the future climate is as yet unclear; but these new findings could change the way we see New Zealand's environmental performance. New Zealand agriculture likely is, in relative terms, one of the largest sources of amines among developed countries. And rates of change of emissions are increasing. Between 1990 and 2009, emissions from agricultural activities increased by about 8 per cent. The implications are tremendous. For instance, one might reasonably argue New Zealand farmers should be entitled to far more carbon credits than foresters receive.

Chris de Freitas is an associate professor in the School of Environment at the University of Auckland.