Grass pollen allergies are a serious health issue. "Peaks in atmospheric grass pollen have been directly correlated to ambulance calls by patients under respiratory stress and ER visits for asthma and wheeze," notes the new study, conducted by researchers at Harvard and the University of Massachusetts, Amherst.
So the paper sought to examine how the production of pollen by grasses would increase in a world where there is expected to be more carbon dioxide -- a key factor in plant photosynthesis -- in the air, but also more ozone (which actually hurts plant growth). To do this, researchers studied Timothy grass, a common grass species whose pollen is often used to test whether people have grass allergies. Pots of the grass were isolated in chambers where greenhouse gas concentrations were set at either 400 parts per million (roughly the current atmospheric level) or 800 parts per million, and ozone levels were similarly varied between a high and low scenario.
Then, the grass grew and pollen samples were bagged and measured. The upshot is that higher levels of carbon dioxide promoted pollen growth considerably -- while ozone did relatively little to hinder it. The researchers therefore calculated that there could be as much as 200 percent more grass pollen in high greenhouse gas concentration scenarios, concluding that "we can expect a large increase in pollen production due to increased CO2 regardless of future ozone levels."
Most people with allergies really don't recognize this is coming, observes study author Christine Rogers of the University of Massachusetts, Amherst. And the health impact, she says, could take two quite different forms. "While it is expected that people with pre-existing allergies will have more pronounced symptoms in the future, we don’t yet know whether this dramatic increase in pollen will also cause more people to develop allergies," explained Rogers.
One partial mitigating factor, of course, is that 800 parts per million of carbon dioxide in the atmosphere is a lot, and hopefully world leaders won't let us get anywhere near that level. The latest report from the UN's Intergovernmental Panel on Climate Change, for instance, suggests that greenhouse gas concentrations must be kept below 450 ppm to stave off severe damage. But that should still have serious health effects, albeit of a lesser scale, says Rogers. "Even an increase to 450 ppm will increase pollen production by around 25 percent and will undoubtedly increase suffering," she says.
Prior research has found that other kinds of pollen, such as from ragweed, will also increase in climate scenarios. But the new research ups the ante, because "grasses are widely abundant in all biomes and grass pollen allergy is highly prevalent worldwide," says Rogers. "Hence the implications of this study are much greater."