Climate change and future pollen allergy in Europe. (2024)

Introduction

Climate change is likely to affect allergic disease (Smith et al.2014), and the view of clinical experts is that these diseases willincrease under climate change (Bielory et al. 2012) in part because ofthe impact on allergenic plant species (Shea et al. 2008). Impacts onallergens may be one of the most important consequences of climatechange for human health (Beggs 2015). Climate change has already beensuggested as one factor behind the increasing prevalence of allergicasthma (Beggs and Bambrick 2005). Pollens are a major cause of symptomsin people with allergic disease, but there is no quantitative assessmentof how future climate change may affect the levels of pollen allergy inhumans because the influence of climate change is complex (Reid andGamble 2009; Smith et al. 2014). For example, an altered climate willaffect the range of allergenic species as well as the timing and lengthof the pollen season, and elevated carbon dioxide (C[O.sub.2]) mayincrease plant productivity and pollen production (Beggs 2015). Climatechange may also affect the release and atmospheric dispersion of pollen(Bielory et al. 2012). The overall impact will be alteration of pollenseason timing and load, and hence, changes in exposure. Modeling all ofthese processes is needed to assess the consequences of climate changeon pollen-related allergic disease. Previous studies (reviewed byBielory et al. 2012) have only examined some of the processes along thispathway.

Allergic disease is a key public health problem that has increasedrapidly in recent decades in both developed and developing countries,and it is now recognized as a major global epidemic (Pawankar 2014;Platts-Mills 2015). The economic burden of allergic disease isconsiderable. In 2007, the total cost of allergic disease to the UnitedStates was 19.7 billion USD, and estimates for the European Union rangefrom 55 to 151 billion EUR (Zuberbier et al. 2014). In terms of specificallergic diseases, the World Health Organization (WHO) estimates that400 million people in the world suffer from allergic rhinitis and 300million from asthma (Bousquet and Khaltaev 2007). Within Europe, theprevalence of pollen allergy in the general population is estimated at40% (D'Amato et al. 2007).

Here, we quantify the potential consequences of climate change onpollen allergy, focusing upon the annual herbaceous plant common ragweed(Ambrosia artemisiifolia) in Europe (henceforth referred to as ragweed).In Europe, ragweed is an introduced species in the middle of an ongoinginvasion event (Storkey et al. 2014) and, therefore, represents a caseof a human population being progressively exposed to a novel allergen.Ragweed is highly invasive; it thrives on disturbed land, with eachplant producing [less than or equal to] 62,000 seeds per year. Ragweedis particularly harmful for public health because each plant produces alarge amount of pollen ([less than or equal to] 1 billion grains a year;Fumanal et al. 2007), and its allergenic potential is high (Taramarcazet al. 2005). Unlike other types of pollen, ragweed pollen peaks in thelate summer (Essl et al. 2015). In some parts of Europe, ragweedgenerates ~50% of the total pollen production. In the United States,where ragweed is native, > 26% of the population is sensitized toragweed (Arbes et al. 2005). This study focuses upon ragweedsensitization as a health consequence. Sensitization occurs when thehuman immune system has synthesized antibodies against the pollen andreacts when reexposed, and it is a major risk factor for allergicdiseases such as allergic rhinoconjunctivitis and asthma (Burbach et al.2009).

Methods

This research is the culmination of a large multidisciplinaryEuropean Commission funded project (Atopica[R]; FP7 grant agreement No.282687). Specifically, for the present analysis, we integrated estimatesof current and future ragweed pollen levels (previously developed withinAtopica[R]) with published data on sensitization rates and populationdensity. To estimate pollen levels, the Atopica[R] group first used aprocess-based model of weed growth, plant population dynamics, andcompetition to project the future expansion of ragweed's rangeunder different climate change scenarios (for details, see Storkey etal. 2014). These range results were then inputted into a system modelingplant invasion, pollen production, pollen release, and the atmosphericdispersion of pollen to simulate current (1986-2005) and future(2041-2060) ragweed pollen levels in Europe (for details, seeHamaoui-Laguel et al. 2015). To provide an estimate of uncertainty,these projections were produced for two different suites of regionalclimate/ pollen models (henceforth, CHIMERE and WRF/RegCM;Hamaoui-Laguel et al. 2015). These projections differ in their drivingglobal climate models and in their representation of dynamical andphysical atmospheric processes. Both model suites used CMIP5 data(Taylor et al. 2012) to account for changing land use patterns. Inaddition, pollen levels were simulated under two alternative greenhousegas concentration scenarios [Representative Concentration Pathway (RCP)8.5, which assumes high emissions, and RCP4.5, which assumes moderateemissions] and three different ragweed plant invasion scenarios (slow,rapid, and reference rates of spread) (Hamaoui-Laguel et al. 2015). Theoutputs from these models were daily ragweed pollen levels for 50 km x50 km grid cells across Europe. Two estimates of current levels wereproduced (based on CHIMERE or WRF/ RegCM), as were 12 estimates offuture levels (based on CHIMERE or WRF/RegCM, plus the 2 RCP and 3 plantinvasion scenarios).

For the present analysis, these 14 estimates of current and futureragweed pollen were combined with health and population data to quantifytheir public health significance using ragweed sensitization rate (RSR)as a health consequence. Sensitization to ragweed is related tolong-term pollen exposure; thus, these daily pollen outputs wereaggregated to provide estimates, on a 50 km x 50 km grid, of averagetotal season ragweed pollen.

To produce quantitative estimates of the potential impact of futureragweed pollen levels on RSRs, we first needed to generate adose-response curve that would be representative of populations inlocations with varying ragweed pollen levels in addition tocharacteristics that might confound the association between pollenlevels and RSRs. Although we considered using estimates from an existingmulticenter study [e.g., from the Atopica[R] project (Atopica[R] 2014),the G[A.sup.2]LEN study (Heinzerling et al. 2009), or the EuropeanCommunity Respiratory Health Survey (ECRHS) (Bousquet et al. 2007)],none of these was considered suitable as they either did not sampleacross a wide range of ragweed pollen levels, focused upon a subset ofthe population, or were restricted to patients with existing allergicdisease.

We instead performed a systematic review of Web of Science,Medline, BIOSIS, the Cochrane library, OpenGrey, and Google Scholar togenerate a pooled estimate of the dose-response curve between ragweedand RSR based on all available studies that met a clearly establishedset of criteria. We used the following major search terms as MedicalSubject Headings (MeSH) and all-field text words, as appropriate:immunology, pollen, aeroallergen, allergy, allergens, atopy, sensitize(or sensitise), sensitized (or sensitised), sensitization (orsensitisation), hypersensitivity, skin test, and Immunoglobulin E. Theinitial search identified 1,923 potentially relevant papers (see FigureS1). A first filter of the search results (see Table S1) retained 50papers that included estimates of RSRs for human populations withinEurope (RSRs for 144 locations in total). Two authors (M.A. and I.L.)independently screened the remaining papers and extracted the followingstudy information using standardized forms: location (country, placename), time period, sample characteristics (number, age, andpopulation-based or allergy patients), the reactivity marker used (e.g.,skin prick test, specific ragweed Immunoglobulin E), and the RSR. Wethen further excluded 15 papers that did not clearly report thesensitivity to ragweed alone, that involved a highly restricted samplepopulation (e.g., institutionalized elderly, weed-sensitive allergypatients, patients with symptoms restricted to the ragweed season), thatwere undertaken more than two decades ago (i.e., pre-1993), or that hada small sample size (< 50 individuals). Finally, for studies thatreported multiple RSRs at a single location (such as a series of annualsensitization observations, observations over several time periods, orobservations for more than one age cohort) we selected a single RSRvalue representing the baseline period and the general population.Ultimately, the review comprised 66 location-specific RSRs from 35studies and 20 European countries (see Table S2).

Each location-specific RSR was matched (on geographic coordinates)to modeled average total season ragweed pollen levels for the baselineperiod (1986-2005) reported by Hamaoui-Laguel et al. (2015). We thenused a generalized linear model to estimate the association between thenatural log-transformed mean pollen level (ln-mean pollen) at eachlocation and the corresponding RSR for that location, adjusting for thestudy population type (general population, i.e., a random sample ofindividuals, or atopic population, e.g., allergy clinic patients).Although we considered adjusting for other factors known to affect RSR(e.g., skin prick test vs. allergen-specific IgE, atopiccharacteristics, and population characteristics such as age and sex),relevant data were often missing. The final model included 63location-specific RSRs after excluding 3 locations with very lowbaseline pollen levels (< 10 grains/[m.sup.3]/year). The resultingmodel coefficient for ln-mean pollen was 5.85 [standard error (SE) 1.10,p-value < 0.001; 95% confidence interval (CI): 3.66, 8.04] with anadjusted [R.sup.2] = 0.384. The coefficient for study type (atopic vs.general population) was 9.35 (SE 3.70, p-value 0.014; 95% CI: 1.94,16.76). A plot of the association between mean pollen counts and RSR,adjusted for study population type, is presented in Figure 1.

We then used the model coefficient and the estimated ln-mean pollencount in each 50 km x 50 km grid cell to estimate an RSR for each gridcell. This operation was performed on our 2 current and 12 futureestimates of ragweed pollen across Europe. We combined the gridded RSRdata with NUTS3 boundaries (subdivisions of the 28 EU countries intoregions of 150,000-800,000 residents) and population data, to estimatethe number of sensitized individuals at the NUTS3 level. These data wereaggregated to the NUTS2 level (regions with 0.8-3 million residents)because many NUTS3 areas are smaller in size than the 50 km x 50 km gridcells. NUTS data were sourced from the Statistical Office of theEuropean Union (Eurostat). For 12 non-EU European countries, we usedboundaries and population data from the Global Administrative Areasdatabase (DIVA-GIS 2015). Projections of population change were obtainedfrom the World Bank databank (World Bank 2015) and applied equally toall NUTS2 areas within a country to estimate population counts for2041-2060.

Burbach et al. (2009) indicated that only a proportion of patientssensitized to ragweed experience symptoms and presented estimates ofclinically relevant sensitization rates for ragweed in differentEuropean countries. These estimates were obtained and were applied atthe country level to the numbers of ragweed-sensitized individuals.

To estimate changes in the severity of ragweed allergy symptoms forsensitized individuals and the time period over which the symptoms areexperienced, we also generated monthly maps of estimated ragweed pollencounts over the pollen season.

Results

The pollen RSR dose-response function was applied to the 14 ragweedpollen maps on a 50 km x 50 km grid, and the corresponding populationsensitized to ragweed at the NUTS2 level was mapped and tabulated atEuropean and country levels. Initially focusing upon the reference plantinvasion scenario, 6 RSR maps and country-level data on the sensitizedpopulation were produced (2 current + 4 future). These differedaccording to the regional climate/ pollen model (CHIMERE or WRF/RegCM),time period (baseline or future), and RCP scenario used. These maps arepresented in Figure S2 and Table S3. Estimates of the sensitizedpopulation based on airborne pollen levels generated using the WRF/RegCM model suite were 27-39% higher than corresponding estimates basedon the CHIMERE model suite for both the baseline period and the futureperiod. A comparison of the spatial patterns of current and futuresensitization indicated that these model divergences were greatest innorth and western Europe (Germany, Belgium, the Netherlands, andFrance), with models generated using the WRF/RegCM model suiteindicating a greater sensitized population because of the higher levelsof pollen in these locations. These results also indicated that thechoice of RCP scenario makes little difference to the results by2041-2060, irrespective of model suite; the sensitized populationsdiffered by only ~5%. To provide an indication of the uncertainty, TableS3 also provides 95% confidence intervals (CIs) based upon the pollenRSR dose-response relationship. These indicate that there is relativelylarge uncertainty regarding the current and future sensitizedpopulation, a consequence of the divergent studies presented in Figure1.

Here, the two model suites are considered to be equally plausiblebecause they both show a similar performance in simulating pollenamounts compared with limited available observations (Hamaoui-Laguel etal. 2015). Therefore, the estimated population affected was averagedacross the two model suites for all further analysis. However, in thenumerical results, the data for both model suites are additionallyreported in square brackets as an indicator of uncertainty; thefollowing format is used: [CHIMERE, WRF/ RegCM]. All subsequent resultsare presented for RCP4.5 (i.e., a moderate degree of climate change) forthe sake of simplicity, bearing in mind that the numbers of sensitizedindividuals in the future are very similar between RCP4.5 and RCP8.5.

Our best estimates of the current and future population sensitizedto ragweed from the pollen RSR dose-response relationship shown inFigure 1 are presented in Figure 2. The sensitized population numbersare presented in Table 1 at the country level and are summed for EU28and non-EU28 countries and for Europe as a whole. Overall, our estimatesindicate that under the RCP4.5 emissions scenario and the referenceragweed invasion scenario, the number of people sensitized to ragweed inEurope would increase from approximately 33 million (27 million and 38million based on CHIMERE and WRF/RegCM, respectively) at baseline to 77million (68 million and 86 million based on CHIMERE and WRF/RegCM,respectively) in 2041-2060 owing to higher pollen counts affecting alarger spatial area. Sensitization is projected to increase in countrieswith an existing ragweed problem, such as Romania and Italy, partly as aresult of increased pollen production by established plant populations;however, the greatest proportional increases are likely to be in areaswhere ragweed sensitization is currently relatively uncommon, such asGermany, France, and Poland. By 2041-2060, sensitization to ragweed willbe widespread across the whole of Europe except for Scandinavia, theBaltic States, most of Spain, Portugal, and Ireland.

Table 1 also examines the impact of ragweed invasion scenario uponsensitization rates. Under the reference plant invasion scenario, thepopulation sensitized to ragweed at the European level is estimated toincrease from 33 million (range: 27 million-38 million) to 77 million(range: 68 million-86 million) by 2041-2060. In comparison, a slow plantinvasion scenario reduces the projected future value to approximately 52million (range: 44 million-59 million), whereas a rapid plant invasionscenario increases the projected value to approximately 107 million(range: 98 million-117 million).

The sensitization rates presented in Table 1 were converted intoestimates of clinically relevant sensitization rates using data fromBurbach et al. (2009). These results are presented in Table S4,indicating that compared with the population sensitized to ragweed, thepopulation clinically sensitized to ragweed in Europe is approximately25% lower for both the baseline and 2041-2060. Table S4 also shows thatfuture changes in the European population base do not greatly affect ourprojections, but they suggest smaller impacts in countries withdecreasing populations such as Germany, Poland, and Romania, andaccentuated impacts in countries with increasing populations (e.g.,France, the United Kingdom).

To estimate the potential impacts of future climate-related changeson allergy symptoms for individuals sensitized to ragweed, maps ofaverage total season pollen (mid-July-mid-October) subdivided intomonthly periods were produced and are displayed in Figure 3. Theseestimates indicate that particularly across France and northwest Italy,airborne pollen is likely to be present much earlier in the season(mid-July-mid-August) because of accelerated plant development. In thepeak pollen months (mid-August-mid-September), more ragweed pollen islikely to be present across Europe, with the greatest increasesoccurring away from current pollen hotspots. Our projections suggestthat pollen will persist in the air across most of Europe in themid-September to mid-October period, likely as a result of delayedfrosts (Storkey et al. 2014).

Discussion

It has been argued that climate change is likely to affectpollen-related allergy (Bielory et al. 2012). To our knowledge, this isthe first study to fully model the potential impacts of climate changeon ragweed plant distribution, plant productivity, and pollen productionand dispersal, as well as the resulting impacts on pollen concentrationsand allergic sensitization.

We estimate that across Europe, sensitization to ragweed is likelyto more than double by 2041-2060 and that populations across most ofEurope are likely to be affected. Our projections indicate thatsensitization will continue to increase in countries with an existingragweed problem, but the greatest proportional increases will be inareas where ragweed sensitization is currently relatively uncommon. Muchof the projected change is due to the expected northward expansion ofragweed, consistent with the expansion already observed in the UnitedStates (Ziska et al. 2011). Our estimates indicate thatragweed-sensitized individuals may experience more severe symptomsbecause of increased ragweed pollen concentrations and a longer pollenseason lasting into September and October across much of Europe. Theseprojected changes are predominantly related to climate and associatedland-use change (66%; Hamaoui-Laguel et al. 2015) but also include thedispersal of this alien plant through Europe even without climatechange.

One striking feature of the results is the large influence of theplant invasion scenario. The reference plant invasion scenario uses thecommon assumption that the flux of seeds is inversely proportional tothe square of the distance (Hamaoui-Laguel et al. 2015). The slow andrapid plant invasion scenarios were generated by altering theproportionality coefficient based upon the ranges reported in previousresearch (Richter et al. 2013). The slow plant invasion scenario assumesa limited expansion in the range of ragweed, and this scenario more thanhalves the overall estimated increase in sensitization to ragweedprojected by 2041-2060 under RCP4.5. Thus, it strongly suggests thatcontrol of ragweed is important for public health and as an adaptationstrategy against the impacts of climate change. However, control ofexisting plants is difficult owing to ragweed's long-lived seeds,to its ability to evolve herbicide resistance, and to its capacity toresprout following cutting (Brewer and Oliver 2009). Ragweed thrives onregular land disturbance; hence, management of land is key to itscontrol (Storkey et al. 2014). Controlling long-distance seed dispersalis also important for preventing plant spread, which is predominantlyassociated with human activity. Therefore, controls over contaminatedseed and monitoring areas prone to ragweed invasion are key elements tolimiting spread (Bullock 2010).

We also examined the impact of different RepresentativeConcentration Pathways (RCP 4.5 and 8.5) and highlighted that thesepathways make little difference to the numbers of individuals sensitizedto ragweed. This outcome is likely to be a result of saturation of theC[O.sub.2] fertilization effect at higher concentrations; it may alsoresult from the relatively similar climate between the two RCPs withinthe relatively short future time frame of our analysis. Projectedchanges to the population numbers and distribution across Europe had arelatively minor influence on our results.

This study emphasizes the multiple steps required to model theimpact of climate change on pollen allergy. There are assumptions anduncertainties associated with each step of the process, and as far aspossible, we have been transparent about them and about their impactsupon the results. We compared two regional climate model suites(WRF/RegCM, CHIMERE) that differ in atmospheric processing, in pollenmodeling, and in the driving global climate model, and we foundresponses in the same direction, although with substantial differencesin magnitude. This finding highlights the need for multimodel approachesto the problem of future pollen simulation. Our research was highlysensitive to the assumptions concerning the plant invasion scenarios,which emphasizes the importance of dispersal control [e.g., the measureshighlighted by Bullock (2010)] as an effective tool to minimize ragweedallergy in the future.

A notable element of uncertainty is the pollen/RSR dose-responserelationship (adjusted [R.sup.2] = 38.4%). This low value is a functionof the limited

number of studies reporting sensitization to ragweed and the lack ofstandardization across studies. We have also assumed that thedose-response relationship between pollen and allergy is identicalacross Europe, whereas differences in factors such as geneticpredisposition may lead to a differential impact across the continent.

In addition to climate change, plant invasion and populationchange, other factors may affect ragweed allergy moving into the future.By 2041-2060, levels of ozone air pollution across Europe are likely todecrease (Colette et al. 2012), potentially suppressing theallergenicity of ragweed pollen (Pasqualini et al. 2011). Conversely,ragweed pollen allergenicity may be elevated through higher atmosphericC[O.sub.2] levels and increasing drought (El Kelish et al. 2014; Singeret al. 2005). Inclusion of changing allergenicity is a priority forfuture research. By 2041-2060, the median age of the European populationis projected to increase from 38 to 52 years (World Bank 2015), andragweed allergy is more difficult to treat in aged populations owing togreater difficulty in diagnosis and limited treatment options because ofcomorbidities and ongoing medication use (Cardona et al. 2011).Appropriate management and use of medication can significantly improveallergy symptoms (Pawankar 2014). Such management can be economicallybeneficial, and appropriate therapy for allergic diseases can be 5% ofthe cost of untreated disease (Zuberbier et al. 2014). Therefore, theoverall impact of increasing ragweed allergy will be influenced by theadaptation capacities of individuals and by those of healthcare systemsacross Europe. Ebi (2014) argued that the capacity of healthcare systemsto adapt to climate change will depend upon the development pathwaystaken by individual countries. Pathways leading to increasedinequalities and fragmentation in society present most of the challengesto adaptation (Ebi 2014) and hence to the potential problem ofincreasing ragweed allergy.

Conclusions

Our projections indicate that ragweed pollen allergy will become acommon health problem across much of Europe and that sensitization toragweed will more than double, increasing from the current total of 33million to 77 million people by 2041-2060. According to our projections,sensitization will increase in countries with an existing ragweedproblem (e.g., Hungary, the Balkans) but the greatest proportionalincreases are projected for countries where sensitization is nowrelatively uncommon (e.g., Germany, Poland, France). Our estimates alsoindicate that sensitized individuals may experience more severe symptomsas a consequence of higher ragweed pollen levels and an extended pollenseason that will last into September and October across much of Europe.Our projections are primarily driven by assumptions regarding climatechange (66%) but also reflect current trends in the spread of thisinvasive plant species across Europe. The projected health consequencesare highly dependent upon the rate at which ragweed spreads, which isstrongly related to control measures against the spread of this plantspecies (Bullock 2010). This relationship emphasizes that control ofragweed spread is essential for public health and as an adaptationstrategy in response to climate change.

To our knowledge, this is the first study to model the futureimpacts of climate change on plant distribution, plant life cycles, andpollen production and dispersal, as well as their subsequent impacts onpollen concentrations and allergy. Climate change consequences will notbe restricted to ragweed, and a recent review has highlighted a range ofother pollen-producing species that may be affected (Beggs 2015). Ourmethods provide a framework for other studies investigating the impactsof climate change on pollen allergy for these other species.

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Iain R. Lake, (1) Natalia R. Jones, (1) Maureen Agnew, (1) Clare M.Goodess, (1) Filippo Giorgi, (2) Lynda Hamaoui-Laguel, (3,4) Mikhail A.sem*nov, (5) Fabien Solomon, (2) Jonathan Storkey, (5) Robert Vautard ,(3,4) and Michelle M. Epstein (6)

(1) School of Environmental Sciences, University of East Anglia,Norwich, United Kingdom; (2) Earth System Physics Section, InternationalCentre for Theoretical Physics, Trieste, Italy; (3) Laboratoire dessciences du climat et de l'environnement (LCSE), l'InstitutPierre Simon Laplace (IPSL), Centre d'Etudes Atomiques-CentreNational de la Recherche Scientifique (CEA-CNRS) l'Universite deVersailles Saint-Quentin (UVSQ), unite mixte de recherche (UMR) 8212,Gif sur Yvette, France; (4) Institut National de l'EnvironnementIndustriel et des Risques, Parc technologique ALATA, Verneuil enHalatte, France; (5) Rothamsted Research, Harpenden, Hertfordshire,United Kingdom; (6) Department of Dermatology, Division of Immunology,Allergy and Infectious Diseases, Experimental Allergy, MedicalUniversity of Vienna, Vienna, Austria

Address correspondence to I.R. Lake, School of EnvironmentalSciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, UK.Telephone: 44 1603 593744. E-mail: [emailprotected]

Supplemental Material is available online (http://dx.doi.org/10.1289/EHP173).

This project was supported by the European Community FrameworkProgramme 7, Atopica[R] (Atopic diseases in changing climate, land useand air quality), grant agreement no. 282687. I.R.L. is funded in partby the National Institute for Health Research, Health ProtectionResearch Unit in Emergency Preparedness and Response at King'sCollege London. The research presented in this paper was carried out onthe High Performance Computing Cluster supported by the Research andSpecialist Computing Support service at the University of East Anglia.

The authors declare they have no actual or potential competingfinancial interests.

Received: 2 October 2015; Revised: 12 January 2016; Accepted: 10June 2016; Published: 24 August 2016.

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Caption: Figure 1. The relationship between ragweed sensitizationrate (percent) and mean pollen level (grains per cubic meter), adjustingfor study population. The solid line represents the best fitrelationship (natural log). a3 locations excluded owing to very lowbaseline pollen levels (< 10 grains/[m.sup.3]/year).

Caption: Figure 2. Percentage of population sensitized to ragweedpollen at baseline and in the far future; averaged results for WRF/RegCMand CHIMERE, RCP4.5, and reference invasion scenario. [C]EuroGeographics for the administrative boundaries.

Caption: Figure 3. Monthly current (baseline) and future(2041-2060) ragweed pollen counts (grains per cubic meter) acrossEurope. Data are the average of the CHIMERE and WRF/RegCM model suitesfor RCP4.5 and a reference plant invasion scenario. [C] EuroGeographicsfor the administrative boundaries.

Table 1. Current and future populations sensitizedto ragweed pollen for three different plant invasionscenarios. Data are average of the CHIMERE and WRF/RegCMmodel suites for Representative Concentration Pathway (RCP)4.5 [CHIMERE and WRF/RegCM values given in brackets]. Population sensitized in thousands [CHIMERE, WRF/RegCM values] 2041-2060 Reference ragweedCountry Baseline invasion scenarioAustria 890 [868, 912] 1,749 [1,636, 1,863]Belgium 923 [732, 1,115] 2,364 [2,143, 2,585]Bulgaria 1,150 [1,135, 1,165] 1,763 [1,614, 1,912]Croatia 873 [804, 943] 1,098 [1,041,1,156]Cyprus 7 [0, 15] 36 [1,71]Czech Republic 487 [409, 565] 1,943 [1,756, 2,130]Denmark 0 [0, 0] 96 [29, 163]Estonia 0 [0, 0] 0 [0, 0]Finland 0 [0, 0] 0 [0, 0]France 3,233 [2,256, 4,210] 10,716 [8,849, 12,582]Germany 4,688 [2,282, 7,095] 15,689 [13,337, 18,041]Greece 831 [487, 1,176] 1,764 [1,341,2,188]Hungary 2,289 [2,668, 1,910] 2,899 [3,069, 2,729]Ireland 0 [0, 0] 4 [0, 8]Italy 4,786 [4,097, 5,474] 10,110 [9,563, 10,656]Latvia 0 [0, 0] 0 [0, 0]Lithuania 0 [0, 0] 6 [11,2]Luxembourg 15 [0, 31] 78 [57, 98]Malta 0 [0, 0] 28 [18, 38]Netherlands 2,224 [1,300, 3,148] 3,489 [2,863, 4,115]Poland 1,123 [1,251,994] 4,397 [4,175, 4,619]Portugal 0 [0, 0] 0 [0, 0]Romania 3,097 [3,045, 3,148] 4,772 [4,473, 5,072]Slovakia 626 [790, 462] 1,160 [1,221, 1,100]Slovenia 304 [281,327] 424 [397, 451]Spain 21 [0, 42] 447 [35, 858]Sweden 0 [0, 0] 13 [1,25]United Kingdom 1,196 [1,008, 1,384] 6,173 [5,113, 7,232]Sum EU28 28,764 [23,413, 34,116] 71,218 [62,743, 79,693]Albania 394 [400, 388] 626 [580, 673]Andorra 0 [0, 0] 2 [0, 5]Bosnia and 703 [682, 724] 914 [869, 958] HerzegovinaIceland 0 [0, 0] 0 [0, 0]Kosovo 259 [196, 323] 429 [391,468]Liechtenstein 1 [0, 1] 3 [1,4]FYR Macedonia 300 [291,308] 486 [449, 524]Montenegro 78 [56, 101] 124 [101, 146]Norway 0 [0, 0] 0 [0, 0]San Marino 2 [2, 2] 5 [5, 4]Serbia 1,708 [1,731,1,685] 2,073 [2,042, 2,105]Switzerland 376 [135, 618] 954 [650, 1,257]Sum non-EU28 3,822 [3,493, 4,151] 5,615 [5,087, 6,144]Sum Europe 32,586 [26,905, 38,266] 76,833 [67,829, 85,837] Population sensitized in thousands [CHIMERE, WRF/RegCM values] 2041-2060 Slow ragweed Rapid ragweedCountry invasion scenario invasion scenarioAustria 1,354 [1,282, 1,427] 2,061 [1,954, 2,169]Belgium 1,616 [1,452, 1,780] 2,767 [2,519, 3,015]Bulgaria 1,442 [1,350, 1,535] 2,066 [1,889, 2,243]Croatia 1,037 [973, 1,102] 1,169 [1,124, 1,214]Cyprus 15 [0, 31] 77 [33, 120]Czech Republic 1,150 [1,054, 1,246] 2,844 [2,737, 2,950]Denmark 3 [0, 7] 533 [426, 640]Estonia 0 [0, 0] 5 [3, 7]Finland 0 [0, 0] 0 [0, 0]France 5,989 [4,480, 7,498] 15,646 [14,066, 17,225]Germany 9,321 [6,882, 11,759] 20,928 [19,129, 22,727]Greece 1,284 [911, 1,658] 2,320 [1,908, 2,732]Hungary 2,721 [2,979, 2,464] 3,006 [3,098, 2,914]Ireland 0 [0, 0] 82 [0, 164]Italy 7,480 [6,846, 8,115] 13,450 [13,079, 13,821]Latvia 0 [0, 0] 77 [78, 75]Lithuania 0 [0, 0] 224 [245, 204]Luxembourg 33 [8, 58] 124 [106, 141]Malta 12 [5, 19] 49 [38, 60]Netherlands 2,894 [2,135, 3,654] 3,862 [3,374, 4,350]Poland 2,437 [2,467, 2,408] 8,733 [8,382, 9,084]Portugal 0 [0, 0] 356 [0, 712]Romania 4,016 [3,796, 4,237] 5,500 [5,062, 5,938]Slovakia 895 [1,004, 786] 1,438 [1,419, 1,457]Slovenia 385 [364, 406] 470 [442, 497]Spain 137 [1,272] 2,670 [939, 4,401]Sweden 0 [0, 0] 153 [114, 192]United Kingdom 2,631 [1,988, 3,273] 10,023 [9,270, 10,776]Sum EU28 46,855 [39,975, 53,736] 100,631 [91,434, 109,828]Albania 513 [496, 529] 784 [727, 840]Andorra 0 [0, 1] 9 [7, 11]Bosnia and 855 [819, 890] 980 [937, 1,023] HerzegovinaIceland 0 [0, 0] 0 [0, 0]Kosovo 347 [287, 407] 498 [492, 504]Liechtenstein 1 [0, 3] 4 [3, 6]FYR Macedonia 395 [369, 420] 584 [562, 605]Montenegro 105 [81, 129] 148 [131, 164]Norway 0 [0, 0] 4 [0, 7]San Marino 4 [4, 4] 6 [6, 6]Serbia 1,964 [1,928, 1,999] 2,140 [2,129, 2,151]Switzerland 650 [346, 954] 1,498 [1,222, 1,774]Sum non-EU28 4,833 [4,331, 5,335] 6,654 [6,216, 7,091]Sum Europe 51,688 [44,305, 59,071] 107,285 [97,650, 116,919]

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