Wednesday, September 10, 2008

Allergic to Climate Change

An item on the ABC World News the other night linking allergies and climate change caught my attention. It referred to a paper in the current issue of The Journal of Allergy and Clinical Immunology describing a connection between climate change and increased levels of pollen production, and thus higher expected incidences of asthma and other allergic maladies. Although the focus of the article was mainly on the future consequences of continued global warming and other environmental impacts, it also looked at changes that are already evident today. That's the angle ABC picked up on, tying the study's findings to a particularly bad allergy season that millions of Americans are experiencing. The key message: if you suffer from pollen allergies, climate change will very likely make them worse--perhaps a lot worse.

Compared with more dramatic outcomes such as droughts, heat waves, rising sea levels, and increased numbers of highly-destructive hurricanes, a bit of hay fever doesn't sound so bad. Having been plagued by allergies for my entire life, I'm not sure I'd agree with that assessment. For many of the one in five Americans who suffer seasonal allergies, it's an important quality of life issue, and for the 20 million afflicted with asthma, this is potentially life-threatening. It's also an anticipated consequence of climate change that could affect people who live far from any coastline or hurricane-affected areas and might otherwise only notice that it's getting a bit warmer. And although hay fever remedies have improved, the good ones are not cheap and still have side effects, while the permanent cure, immunotherapy, requires a significant commitment of time and can trigger some unpleasant allergic reactions along the way.

The mechanisms underlying the study's finding of increased seasonal allergies are pretty simple. Higher atmospheric CO2 levels cause vegetation to grow faster and larger--though apparently not to the degree previously thought. Unfortunately, that also seems to apply to plants like ragweed, resulting in bigger weeds emitting more pollen. Now throw in warming average temperatures, bringing earlier spring-like conditions and longer growing seasons. Whatever that combination might do for crop productivity, we should also expect to apply to less desirable plants and their pollen counts.

While that prospect merits concern, it's also important to understand the limitations of this study. A glance at its contents reveals that it was not a clinical report on allergy patients over time, but rather a literature search on the mechanisms of climate change, plant biology, and allergic and asthmatic responses to various allergens. It draws many of its assumptions about the expected course of climate change from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, of Nobel Peace Prize-sharing fame. That won't satisfy all critics, but we ought to be relieved that the four MDs who authored the paper didn't attempt to reinvent climate theory for themselves.

I'm well aware from the comments I receive that my readers are not uniformly worried about climate change. Some remain skeptical of the evidence for human responsibility, and a few doubt we are even warming in any discernible way, or think the globe might now be cooling. But whether you buy the whole enchilada, or only part of it, it's worth considering that climate change is beginning to alter our world in ways large and small, predictable and surprising, and that even if it doesn't drown all our coastal cities and dry up our crops, it could still make the earth into a much less hospitable place than the environment that enabled our ancestors to move beyond hunting & gathering, build cities and civilizations, and expand our population a thousandfold. More severe allergies aren't the worst alteration we can imagine, but this looks like yet another factor to which we and our descendants must adapt, if we don't get our emissions under control.

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