Climate change would be responsible for two thirds of this increase, the remaining third would be due to the colonization of the plant as a result of human activities. These estimates, made by a European team of researchers, show that it is now necessary to establish coordinated management of this invasive plant in Europe followed by long-term pollen and mapping the presence of plants. These estimates are published in the journal Nature Climate Change May 25, 2015.
Ragweed pollen is highly allergenic plant, of North American origin. The main clinical manifestations of allergy caused by this plant are rhinitis, conjunctivitis, and asthma. The pollen peak of this plant, which has already settled in France Burgundy, Auvergne and the Rhone-Alpes region, in August and September, which extends the period of allergies up to autumn for all sensitive people. Several studies have shown that global warming will allow Ambrosia to settle in areas where the climate did not previously favor it, without quantifying the increase in concentrations of pollen in the air.
The geographical evolution of air contamination by pollen depends on several factors: the plant's ability to reach new territories via various dispersion phenomena of its seeds, and climate change that allows the plant to flourish in these new territories. To predict the effect of climate and different seed dispersal modes on the atmospheric concentration of pollen, the researchers used several types of numerical models. They first model simulates climate change based on the amount of greenhouse gases that may be emitted in the coming years by human activities. The second models the invasion of the plant, the production and release of pollen, and their dispersion in the air. With these models, which were used to test different scenarios for the dissemination of seeds and climate change, the researchers determined that the factor of increasing concentrations of ragweed pollen would be an average of four by 2050. To confirm the stated trends, which involve a degree of uncertainty, it is necessary to establish long term monitoring of these pollens and map the evolution of the presence of plants in Europe.
With this study, the researchers also determined the responsibilities of each of these factors in the increase of pollen in the air. Seed dispersal, whether natural, with water trickling and streams, or human via road transport, railways and agricultural practices, is responsible for a third of the increases in the concentration of pollen. Climate change is meanwhile responsible for two thirds. On the one hand, it promotes the expansion of ragweed in North and North-East Europe in particular. On the other hand, its effect is expressed mainly by the increase in pollen production induced by the increase of CO2 and its favorable effect in the development of vegetation.
Bullet points:
• 1/3 and 2/3s is our "best estimate".
• The factor 4 (between 2 and 12) assumes median dispersal rate, but it it will certainly grow.
• The robust messages:
o large potential growth and expansion
o relative insensitivity to climate scenarios
o clear sensitivity to seed dispersal, the CO2 effect, ...
These results, obtained in the framework of the European project Atopica also pave the way for a new generation of short-term forecasting tools for pollen concentrations and should eventually allow for the inclusion of Ambrosia alerts for prevention against allergy.