Human health and food production are being damaged because too little is being done to control worldwide ozone levels, a report by the Royal Society says.
Ozone forms a protective layer that helps to block ultraviolet radiation high in the atmosphere, but at ground level it is a significant pollutant and a contributor to global warming.
Regulations to control the gas have been introduced by Britain and other industrialised nations but it is still present in quantities well above safe levels, largely because it is carried by air currents from other parts of the world. Levels close to the ground have risen 6 per cent each decade since the 1980s, the Royal Society says in its report, which calls for concerted international action.
Ozone is formed by the reaction between sunlight and chemicals - some naturally occurring and others from pollutants - in the air. Sources of ozone-promoting pollutants include vehicle exhaust fumes and shipping.
Children and the elderly are especially vulnerable to adverse reactions to ozone, which affects the eyes, lungs and nose. An estimated 1,582 people died in 2003 because of the effects of ozone. Deaths are conservatively forecast to rise by 51 per cent to 2,391 by 2020 because of pollution and climate change.
European Union nations, the United States and Japan have all managed to reduce the frequency of peak levels of ozone pollution but have failed to eradicate them.
Peaks occur during hot, sunny and stagnant conditions and can be particularly dangerous when they exceed 100 parts per billion (ppb). Background levels, which are 35-40 ppb in Britain, are worrying scientists because of their effects on human health and crop yields.
David Fowler, chairman of the Royal Society's ground level ozone working group, said: 'Weather systems and jet streams transport ozone, and the pollutants that lead to its formation, often far from their point of origin. Here in the UK, for example, we receive most of our ozone from outside of Europe.
'Until we have a globally co-ordinated approach that addresses the international nature of the problem, national and even regional level controls are unlikely to deliver the kind of reductions that are necessary to protect human health and the environment.'
Significant reductions in crop yields because of ozone have been observed in Europe and North America, with £5 billion being knocked off the value of arable crops in Europe in 2000 alone. The nutritional values of wheat, rice and soya bean are all known to be reduced by the chemical.
The Royal Society report, published today, estimates that crop losses will increase over the next 30 years.
In regions including South Asia the losses to crops such as wheat and rice are forecast to be so serious that they may cause food shortages.
Climate change, the report says, will exacerbate the problem by increasing the quantities of ozone produced at ground level. It is also a greenhouse gas so will help to intensify climate change.
Professor Fowler added: 'Ozone has become a global pollutant, with direct effects on human health, crop production, ecosystems and climate, yet control strategies are country or region based.
'A co-ordinated global strategy bringing ozone into international frameworks for controlling air pollutants and greenhouse gases is required. The reduction of methane emissions would, for example, contribute both to the reduction of climate change and ozone pollution, and all of the associated ecological and human health effects.'