June 14, 2015, by Tim Radford
Ragweed may look harmless, but it can worsen asthma and other conditions
Image: Harry Rose, South West Rocks, Australia, via Wikimedia Commons
Europeans affected by asthma and other breathing problems face pollen counts four times higher than today’s by mid-century, because of an invasive plant. LONDON, 14 June, 2015 − Alien migrants, driven by climate change and taking advantage of local benefits, have started to settle in Europe, and they are not likely to be popular. Ambrosia artemisiifolia, a ragweed from North America, produces potent allergens likely to trigger a number of unwelcome symptoms, and pollen counts are expected to quadruple by 2050. This is not good news for those people vulnerable to rhinitis, conjunctivitis, tracheitis and asthma. Ragweed has already taken root in Burgundy, Auvergne and the Rhone-Alpes region of France, and it tends to produce its peak pollen in August and September. Lynda Hamaoui-Laguel of the Laboratory for the Sciences of Climate and the Environment in Gif-sur-Yvette in France and colleagues report in Nature Climate Change that they thought about seed production, pollen production and the wind that drives the dispersal of pollen, and then used computer simulations to model concentrations by 2050, under a range of possible climate change scenarios. There are all kinds of uncertainties in such calculations, but they found that, at the very least, airborne pollen concentrations would be twice as high; at the extreme outside, they could grow twelvefold. But the likelihood was that 35 years onward, the pollen counts would have quadrupled. The spread of the invader − along with the prevalence of late summer sneezing, watery eyes and breathing problems − would increase in north-central Europe, northern France and the southern United Kingdom, where, for the time being, the pollen counts of ragweed are barely detectable.
The researchers reckon that about a third of the spread of the plant will be due to seed dispersal: that is, the invader would be on the march even without climate change. Humans would accidentally transport the seeds along road and rail routes, and weeds would spring up along agricultural land. The invader arrived from North America some time in the 19th century (it also made it to Australia, South America and East Asia) but in Europe it is concentrated mostly between the latitudes of 42° and 47° North, in northern Italy, south-eastern France and the Pannonian plain embraced by the Carpathian mountains in east-central Europe. Two-thirds of its future spread, however, will happen because of changes in land use and because of climate change. That is, northern Europe will become more welcoming, and greater concentrations of carbon dioxide in the atmosphere – itself a consequence of the burning of fossil fuels – will make the plant more productive of pollen. The scientists warn, too, that the ragweed pollen itself might become more potent as a promoter of allergies. “Once established, ragweed is difficult to eradicate because of its long-lived seed, its capacity to re-sprout after cutting and its propensity to evolve resistance to herbicides,” they warn. “Our results indicate that controlling the current European ragweed invasion will become more difficult as the environment will be more favourable for ragweed growth and spread, highlighting the need for the development of effective and regionally co-ordinated eradication programmes.” − Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.