Expert warning on ragweed pollen
Climate change could help a notorious invasive weed known to trigger severe allergy attacks gain a foothold in the UK, experts have warned.
Ragweed (Ambrosia artemisiifolia) is native to North America but since the 1960s has spread rapidly across warmer parts of Europe.
It is still rare in the UK - but by 2050 could be scattering pollen throughout much of England, afflicting new levels of hay-fever misery on susceptible individuals, new research suggests.
Pollen from the plant not only induces severe allergic reactions but also extends the hay-fever season from summer to autumn.
Last year, researchers from the University of Leicester recorded airborne ragweed pollen levels in the East Midlands high enough to cause significant hay-fever attacks.
The weed is a far more potent allergy trigger than grass and experts fear it could pose a serious public health problem if it becomes established.
Scientists writing in the journal Nature Climate Change found that predicted levels of global warming were likely to create conditions favourable to ragweed across large areas of northern Europe, including the UK.
They concluded: "Climate change and ragweed seed dispersal in current and future suitable areas will increase airborne pollen concentrations, which may consequently heighten the incidence and prevalence of ragweed allergy."
The researchers, led by Dr Lynda Hamaoui-Laguel, from the Laboratory of the Sciences of Climate and the Environment in Gif sur Yvette, France, ran computer simulations that forecast a four-fold increase in European ragweed pollen concentrations by 2050.
"Substantial increases" in pollen load were likely to occur in areas such as north-central Europe, northern France and southern England, where ragweed was rare today.
Depending on the speed of dispersal, pollen levels in some locations could rise as much as 12 times.
The northern spread of ragweed was expected regardless of whether a high or moderate level of global warming occurred.
The scientists added: "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.
"Our results indicate that controlling the current European ragweed invasion will become more difficult in the future 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."
Ragweed is a prolific pollen producer - one plant is capable of generating up to a billion pollen grains per season.
Its wind-blown pollen can travel hundreds of miles and is also resilient enough to survive through a mild winter.