As Emissions Rise, Weeds (And Allergies) Could Follow Suit

from Wildlife Promise

The current issue of Natural History magazine features a fine story by Peter Del Tredici on the role of weeds in the modern city. The broad discussion, about the relevance of the idea of an ‘invasive’ plant in an environment where very little truly native vegetation remains, is worth your time.

One of the subjects that most interests Del Tredici is the weed’s place in a world whose climate we are rapidly changing. PDF available on his website:

As many scientists have pointed out, modern climate change can be viewed as a massive, uncontrolled experiment on the impact of increased atmospheric carbon dioxide (CO2) concentrations on Earth’s ecosystem.

[T]this is where the cities come in: they have already arrived at the future in terms of experiencing higher concentrations of CO2 than the surrounding countryside.

Planting trees and other vegetation in cities is seen as a vital tool for fighting emissions via carbon sequestration. Spontaneous urban plants—what we think of as ‘weeds’ chief among them—will probably be a big part of this, owing largely to their extreme adaptability. As Del Tredici explains, weeds “[provide] a greater return in terms of carbon sequestration per maintenance dollar spent than most intentionally cultivated species.”

There is, of course, a rather sizable catch:

As every sufferer of hay fever knows all too well, however, plants do not always enhance the quality of life for the human inhabitants of cities. If recent research is any guide, climate change could well make some of those negative interactions worse than they currently are. Controlled experiments with two infamous native plants—ragweed and poison ivy—have shown that elevated levels of CO2 induce the former to emit significantly more of its highly allergenic pollen and cause the latter to produce higher concentration of its irritating toxins.

So, this is complicated. Weeds could help mitigate carbon pollution, but they will be the same plants that thrive with worsening global warming and, in turn, make allergy sufferers suffer…harder.

Above: your future overlord? ( flickr | Carolina Biological Supply Company )

As noted in an April report from NWF, global warming is expected to intensify respiratory allergies for about 25 million Americans. Ragweed plants, which are projected to thrive and become more irritating with increased emissions, “are likely produce about twice as much pollen as they would have 100 years ago” at modern carbon pollution conditions.

In addition to bringing much human suffering, this phenomenon could cost us dearly in economic terms. According to the report, allergies and asthma cost the U.S. “nearly $33 billion annually in direct health care costs and lost productivity.”

For folks who cling to inhalers and haze-inducing medication during allergy season, this is a bleak picture. For those of us who don’t—Whoo! Finally, some good genes!—there’s always this (PDF):

Poison ivy also grows faster and is more toxic when carbon dioxide increases in the atmosphere. More than 350,000 cases of contact dermatitis from exposure to poison ivy are already reported in the United States each year. These numbers are likely to increase if poison ivy grows faster and becomes more abundant. The reactions may also become more severe because poison ivy produces a more potent form of urushiol, the allergenic substance, when carbon dioxide levels are higher.

Ah, drat. I’m really, really bad at not scratching.

For even more on the itchy and bitey things projected to run wild with worsening climate change, see our Climate Invaders report and accompanying video.