The future may spring a nasty surprise on hay fever sufferers and create ecological havoc in the plant world, writes Steve Farrar.
Scientists have found evidence that rising concentrations of carbon dioxide in the atmosphere could lead to a surge in the amount of pollen.
The study, published in the journal Annals of Allergy, Asthma and Immunology , focused on ragweed, producer of one of the most common allergens in the northern hemisphere.
Ragweed plants were grown from seeds in two different enclosed environments. One had 350 parts carbon dioxide per million of air, which is about the current level. The other had 700 parts carbon dioxide, a level that many experts have forecast could occur between 2050 and 2100 as a result of pollution.
Paul Epstein, associate director of the Center for Health and Global Environment at the Harvard Medical School in the United States, and colleagues found that the plant in the enriched atmosphere produced 61 per cent more pollen.
While most attention has been directed towards the impact on temperature and climate of a rise in atmospheric carbon dioxide levels, the new study suggests there will be other consequences.
"The side-effects of carbon dioxide, as well as its impact on heat budget and the water cycle, have to be taken very seriously," Dr Epstein said.
The resulting increase in pollen production echoed another study in which carbon dioxide was pumped into a pine forest, prompting a three-fold rise in pine cone and seed production.
Dr Epstein said the study suggested that plants may be responding to the carbon dioxide-enriched conditions to enhance reproductive success.
Beyond the impact on human health, the study implies that ecological balances between competing species could be thrown into chaos, with more weedy plants gaining a relative reproductive advantage.