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Commentary February 2009 | Volume 117 | Issue 2

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Environ Health Perspect; DOI:10.1289/ehp.11501

Rising CO2, Climate Change, and Public Health: Exploring the Links to Plant Biology

Lewis H. Ziska,1 Paul R. Epstein,2 and William H. Schlesinger3

Author Affiliations open
1U.S. Department of Agriculture Agricultural Research Service, Crop Systems and Global Change Laboratory, Beltsville, Maryland, USA; 2Center for Health and the Global Environment, Harvard Medical School, Boston, Massachusetts, USA; 3Cary Institute of Ecosystems Studies, Millbrook, New York, USA

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  • Background:

    Although the issue of anthropogenic climate forcing and public health is widely recognized, one fundamental aspect has remained underappreciated: the impact of climatic change on plant biology and the well-being of human systems.


    We aimed to critically evaluate the extant and probable links between plant function and human health, drawing on the pertinent literature.


    Here we provide a number of critical examples that range over various health concerns related to plant biology and climate change, including aerobiology, contact dermatitis, pharmacology, toxicology, and pesticide use.


    There are a number of clear links among climate change, plant biology, and public health that remain underappreciated by both plant scientists and health care providers. We demonstrate the importance of such links in our understanding of climate change impacts and provide a list of key questions that will help to integrate plant biology into the current paradigm regarding climate change and human health.

  • Citation: Ziska LH, Epstein PR, Schlesinger WH. 2009. Rising CO2, Climate Change, and Public Health: Exploring the Links to Plant Biology. Environ Health Perspect 117:155–158;

    Address correspondence to L.H. Ziska, Building 1, Room 323, Crop Systems and Global Change Laboratory, USDA-Agricultural Research Service, 10300 Baltimore Ave., Beltsville, MD 20705 USA. Telephone: (301) 504-6639. Fax: (301) 504-5823. E-mail:

    We thank J. Bunce for useful comments and suggestions.

    The authors declare they have no competing financial interests.

    Received: 24 March 2008
    Accepted: 19 September 2008
    Advance Publication: 19 September 2008
    Final Publication: 1 February 2009

The concentration of atmospheric carbon dioxide has increased by 22% since 1960 to a current background level of approximately 385 μmol/mol (Intergovernmental Panel on Climate Change 2007). Recent evidence that the growth rate of CO2 emissions may have jumped from 1.3% to 3.3% per year from the 1990s to 2000–2006, potentially as a result of declining global sinks and increased economic activity, emphasizes the critical need to characterize the probable impacts of this impending climate forcing on human systems (Canadell et al. 2007).

Because CO2 absorbs heat leaving the earth’s atmosphere, there is widespread agreement that increasing CO2 is projected to result in increasing surface temperatures and wider swings in weather. The extent to which temperatures increase and weather patterns shift and the potential consequences for human health, from heat-related deaths to the spread of vector-borne diseases, have been addressed in the scientific literature (Epstein 2005; Gamble et al. 2008; Patz and Kovats 2002). Here we describe additional dimensions of global environmental change: the response of terrestrial plants to the buildup of atmospheric CO2, potential climatic forcing with respect to temperature on plant growth, and the implications for human health and nutrition.

Plant biology is directly affected by rising CO2 because CO2 is the sole supplier of carbon for photosynthesis. Because approximately 95% of all plant species are deficient in the amount of CO2 needed to operate at maximum efficiency, recent increases in CO2 have already stimulated plant growth, and projected future increases will continue to do so (e.g., Poorter 1993), with the degree of stimulation being at least potentially temperature dependent (Long 1991). Critics of the potential of CO2 as a greenhouse-warming gas have stressed that CO2-induced stimulation of plant growth will result in a lush plant environment (Idso and Idso 1994); indeed, much of the literature has focused on agronomically important species (see, e.g., Ainsworth et al. 2002; Kimball 1993). However, CO2 does not discriminate between desirable (e.g., wheat, rice, and forest trees) and undesirable (e.g., ragweed, poison ivy) plant species with respect to human systems.


What aspects of plant biology currently affect public health? How have, or will, changing levels of CO2 and increasing surface temperature change those aspects? For many health care professionals, the role of plant biology has not been fully elucidated, yet it has a number of self-evident impacts, such as nutrition, and perhaps more subtle interactions, such as the spread of narcotic plant species, that deserve our consideration and attention.


Aerobiology. One of the most common plant-induced health effects is related to aerobiology. Plant-based respiratory allergies are experienced by approximately 30 million people within the United States (Gergen et al. 1987). Symptoms include sneezing, inflammation of nasal and conjunctival membranes, and wheezing. Complicating factors, including nasal polyps or secondary infections of the ears, nose, and throat, may also occur. Severe complications include asthma, cardiac distress, chronic obstructive pulmonary disease, and anaphylaxis.

Quantity and seasonality of pollen are likely to be affected by both climate forcing of phenology and direct effects on pollen production. Overall, three distinct plant-based inputs relate to pollen production: trees in the spring, grasses in the summer, and ragweed (Ambrosia spp.) in the fall. In Europe, a 35-year record for birch (Betula spp.), a known source of allergenic tree pollen, indicates earlier spring floral initiation and pollen release with anthropogenic warming (Emberlin et al. 2002). At present, the role of seasonality and/or rising CO2 on pollen production in grasses remains unknown. Warming has been shown to increase pollen production of western ragweed by 84% (Wan et al. 2002). Initial indoor studies examining the response of ragweed to recent and projected changes in CO2 demonstrated an increase in both ragweed growth and pollen production (Rogers et al. 2006; Wayne et al. 2002; Ziska and Caulfield 2000); increased CO2 stimulates ragweed pollen production several times more than it stimulates overall growth, and the pollen produced may be more allergenic (Singer et al. 2005). Outdoor experiments that exploited an urban–rural transect also showed the sensitivity of ragweed pollen production to CO2in situ (Ziska et al. 2003). In addition, recent research on loblolly pine (Pinus taeda) at the Duke University Forest Free-Air CO2 Enrichment (FACE) site demonstrated that elevated CO2 concentrations (200 μmol/mol above ambient) resulted in early pollen production from younger trees and greater seasonal pollen production (LaDeau and Clark 2006). Besides increased pollen exposure, other consequences of increased fossil fuel burning may be synergistic; for example, diesel particles help deliver aeroallergens deep into airways and irritate immune cells, whereas early arrival of spring and late arrival of fall may extend tree and ragweed allergy seasons, respectively (Ziska et al. 2008a).

Alternatively, more subtle interactions regarding plants may be related to indirect effects of CO2 on fungal decomposition. For example, increasing CO2 concentration resulted in a 4-fold increase in airborne fungal propagules, mostly spores (Klironomos et al. 1997). The link between spore formation, potential changes in allergenicity of the spores, and the mechanism associated with spore release in the context of elevated CO2 has not been entirely elucidated; however, direct effects on microbial function and litter decay seem a likely possibility.

These data suggest a distinct role regarding climate forcing and rising CO2 (both at the local urban level, and projected globally) on pollen/spore exposure among the general population. Although the epidemiology of allergic rhinitis is complex, depending on both economic and sociologic factors, the current data also indicate a well-defined role of plant biology in the spread of asthma and respiratory disease. Such associations may help explain the quadrupling of asthma in the United States since 1980 (American Academy of Allergy Asthma and Immunology 2000).

Contact dermatitis. More than 100 different plant species are associated with contact dermatitis, an immune-mediated skin inflammation. Chemical irritants can be present on all plant parts, including leaves, flowers, and roots, or can appear on the plant surface when injury occurs. One well-known chemical is urushiol, a mixture of catechol derivatives. This is the compound that induces contact dermatitis in the poison ivy group (Toxicodendron/Rhus spp.). Currently, sensitivity to urushiol occurs in about two of every three people, and amounts as small as 1 ng are sufficient to induce a rash. More than 300,000 people yearly in the United States suffer from contact with members of the poison ivy group (e.g., poison ivy, oak, or sumac) (Mohan et al. 2006). The amount and concentration of these chemicals vary with a range of factors, including maturity, weather, soil, and ecotype. Recent research from the Duke FACE facility also indicated that poison ivy growth and urushiol congeners are highly sensitive to rising CO2 (Mohan et al. 2006). Overall, these data suggest plausible links among rising CO2, plant biology, and increased contact dermatitis. At present, potential interactions with warmer temperatures and longer growing season in relation to biomass and urushiol content are unknown.

Toxicology. More than 700 plant species are poisonous to humans. Similar to dermatitis, the presence of toxic substances is related to specific plant organs (fruit, leaf, stem), and edible and poisonous parts can exist on the same plant (e.g., rhubarb, Rheum rhabarbarum, and potato, Solanum tuberosa). Bracken fern (Pteridium aquilinum) may represent a toxicologic threat because of production of potential carcinogenic spores or exudates (Trotter 1990). Poison hemlock (Conium maculatum), oleander (Nerium aleander), and castor bean (Ricinus communis) are so poisonous that tiny amounts can be fatal if ingested (e.g., ricin in castor bean has a greater potency than cyanide). Ingestion of plant material continues to be a very common exposure for humans (particularly children) and can account for nearly 100,000 calls to national poison centers annually (Watson et al. 2004). Pediatric patients comprise more than 80% of plant-related exposures. Only a few plants are associated with potentially life-threatening toxicity, and < 20% of plant exposures require medical treatment (Watson et al. 2004). However, the impact of CO2 on the concentration or production of such poisons is almost completely unknown. Rising temperature and longer growing season would, a priori, increase the presence of such species in the environment, but, here too, little is known regarding the interaction between CO2 and toxicology.

Pharmacology. Plants have been used for healing since the beginning of civilization. Diversity in the production of secondary chemical products remains an important source of existing and new metabolites of pharmacologic interest (Table 1). Even in developed countries, where synthetic drugs have replaced herbal medicines, 25% of all prescriptions dispensed from community pharmacies from 1959 through 1980 contained plant extracts or active principles prepared from higher plants (e.g., codeine; Farnsworth et al. 1985). For developing countries, however, the World Health Organization (WHO) reported that > 3.5 billion people, or more than half of the world’s population, rely on plants as components of their primary health care (WHO 2002).

Table 1Table 1 – A partial list of plant-derived pharmaceutical drugs and their clinical uses.

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Less than 1% of terrestrial plant species have been examined in-depth for their possible pharmacologic use (Pitman and Jorgensen 2002), and only a handful of studies have examined how pharmacologic compounds might respond to recent or projected changes in CO2 and/or temperature. Among these, growth of wooly foxglove (Digitalis lanata) and production of digoxin were increased at 1,000 μmol/mol CO2 relative to ambient conditions (Stuhlfauth and Fock 1990). Production of morphine in wild poppy (Papaver setigerum) (Ziska et al. 2008b) (Figure 1) showed significant increases with both recent and projected CO2 concentrations. Concurrent increases in growth temperature and CO2 also affected the production and concentration of atropine and scopolamine in jimson weed (Datura stromonium) (Ziska et al. 2005); however, a synergistic effect on either concentration or production was not observed.

Figure 1Figure 1 – Changes in morphine production and concentration (mean ± SE) from wild poppy (Papaver setigerum) as a function of rising levels of atmospheric CO2 (Ziska et al. 2008b), corresponding roughly to atmospheric concentrations from 1950, today, and those projected for the years 2050 and 2090, respectively. Different letters indicate significant differences as a function of CO2 concentration using Fisher’s protected least significant difference.

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Food security/nutrition. Adequate diet and nutrition remain key aspects of global health. Among climatic factors, two are likely to have severe consequences for agricultural productivity: water and temperature. Flowering is one of the most thermal-sensitive stages of plant growth (e.g., Boote et al. 2005). Chronic or short-term exposure to higher temperatures during the reproductive stage of development can have negative affects on pollen viability, fertilization, and grain or fruit formation relative to vegetative growth (Hatfield 2008). In addition, water supply, particularly water for irrigation, is at risk with declining ice and snow reserves in mountainous regions (e.g., Kerr 2007). Irrigation is vital to maintaining food security in populous regions in East Asia and elsewhere. Conversely, warmer temperatures and additional CO2 could extend growing seasons and boost production; however, there is concern that concurrent increases in CO2 and temperature could further exacerbate reproductive sterility because of the indirect effect of CO2 on transpirational cooling at the canopy level (Horie et al. 2000; Prasad et al. 2006). With respect to nutrition, plants are anticipated to become more starchy but protein-poor, with a subsequent decline in digestibility as CO2 increases (Hesman 2002). In paddy rice, percent protein decreased with both increasing air temperature and higher CO2 concentrations over a 2-year period (Ziska et al. 1997). Increasing CO2 from preindustrial to current levels resulted in decreased protein in both spring and winter wheat (Rogers et al. 1998); other experiments have also shown a CO2-induced reduction in flour protein concentration, as well as changes in optimum mixing time for bread dough, and bread loaf volume (Kimball et al. 2001). Alternatively, strawberries have shown a positive increase in antioxidant capacity and flavanoid content in response to elevated CO2 levels (Wang et al. 2003), and mung bean has shown an increase in omega-3 fatty acid content (Ziska et al. 2007).

Spread of human disease. Plants are not disease vectors per se, but animal reservoirs of disease spread, notably rodents and mosquitoes, rely on plants as a principle food source (although female mosquitoes require blood proteins in order to lay eggs). Given that plant growth, pollen, and seed production among annual plants (including weeds) are likely to increase in response to CO2 (Patterson 1995) and warmer temperatures (Wan et al. 2002), greater availability of food supply could result in a higher abundance of these animal vectors, with consequences for disease epidemiology. Pollen on open ponds, for example, can serve as food for mosquito larvae (Ye-Ebiyo et al. 2000); however, it is unclear if CO2-induced qualitative changes in pollen (Singer et al. 2005) could also affect mosquito fecundity.

Pesticide, herbicide, and fungicide use. Chemical control is the principal means of weed management in most developed countries. Therefore, it is reasonable to ask whether current control efforts could limit any potential or probable impact of climatic forcing or CO2-induced changes in plant biology and public health. Temperature and precipitation are known abiotic factors that can affect chemical application rates and overall efficacy (Patterson 1995). There is also evidence from a limited number of studies that rising CO2 levels can decrease chemical efficacy for the control of annual and perennial weeds (Figure 2) (Archambault 2007; Ziska and Runion 2007). For Canada thistle, CO2-induced reductions in efficacy of glyphosate application were related to greater carbon allocation to roots and a reduction in the systemic effect of the herbicide (Ziska et al. 2004). However, it is not clear if this is a ubiquitous response among perennial weeds. Overall, pests, pathogens, and weeds currently consume some 42% of growing and stored crops annually (Pimentel 1997), and this figure could escalate as a result of higher CO2, warming, altered precipitation patterns, and more weather extremes. Increased use of petrochemicals for control carries further risks for human and animal health because it could increase the presence of these chemicals in the environment.

Figure 2Figure 2 – Change in growth rate (g dry matter/day) for weedy species after application of herbicide at recommended doses, when grown at current CO2 levels (A) and at elevated (600–800 μmol/mol) CO2 levels (B). At elevated CO2 levels (B), all growth rates were significantly greater relative to plants that received the same dosage grown at ambient (370–400 μmol/mol) CO2 levels (A). Herbicide was glyphosate in all cases except where indicated. Increased spraying frequency could overcome CO2-induced reductions in efficacy but could increase residual effects within the environment.

aGlufosinate was active ingredient.

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Uncertainties and limitations. As atmospheric CO2 continues to increase, we can expect fundamental changes in plant biology and plant communities, either from anticipated changes in temperature and other abiotic parameters related to climatic forcing, or directly from CO2-induced changes in physiology and growth. From the initial studies described here, it is evident that there are a number of plant-based links between such anthropogenic perturbations and public health. Yet, there are a number of key questions that remain to be addressed by the scientific community. What other plant species are likely to increase pollen production in response to CO2/temperature increases? How will this affect the epidemiology of allergies/asthma? Will contact dermatitis increase for the general population? Can we expect toxicologic changes in poisonous plants? How will CO2-induced changes in food quality affect human nutrition and health? Is the quality or efficacy of plant-based medicines increasing or decreasing? How might CO2 and/or climate alter the spread and production of narcotic plants? As plant distribution changes with CO2/climate change, how will this affect the ability of mosquitoes or rodents to spread disease? If weed growth is responsive to increasing CO2 and increased levels of herbicides are needed for control, how will this affect levels of pesticides in the environment? What steps must we take to ensure food security and adequate nutrition? None of these questions have been addressed in depth; few field data are available that assess both CO2 and temperature concurrently with respect to these questions.


There is a concerted effort among academic and government institutions both to recognize the degree of health risk posed by climate change and to formulate strategies to minimize adverse impacts (for reviews, see Burns 2002; Epstein and Mills 2005; McMichael et al. 2006; Patz and Kovats 2002). However, in these assessments, the role of plant biology in human health has been largely ignored.

We suffer in many ways by what can be called “plant blindness.” That is, when we look at nature, we are more likely to recognize the diversity of animals and only acknowledge plants as a sort of “green background.” Yet, that green background—essential habitat—is highly dynamic. It affects every aspect of our lives, from air, water, clothing to shelter and medicine. The ongoing increase in CO2 and its projected impact on temperature and climate represent a clarion call to consider plant interactions beyond the realm of agriculture. Assessing the scale and potential impact of these interactions between plant biology and public health is a facet of human-induced climatic forcing that is under appreciated.


AAAAI. 2000. The Allergy Report. Milwaukee, WI:American Academy of Allergy Asthma and Immunology.

Ainsworth EA, Davey PA, Bernacchi CJ, Dermody OC, Heaton EA, Moore DJ, et al. 2002. A meta-analysis of elevated [CO2] effects on soybean (Glycine max) physiology, growth and yield. Global Change Biol 8:695–709.

Archambault DJ. 2007. Efficacy of herbicides under elevated temperature and CO2. In: Agroecosystems in a Changing Climate (Newton PCD, Carran RA, Edwards GR, Niklaus PA, eds.). Boca Raton, FL:CRC Press, 333–336.

Boote KJ, Allen LH Jr, Prasad PV, Baker JT, Gesch RW, Snyder AM, et al. 2005. Elevated temperature and CO2 impacts on pollination, reproductive growth, and yield of several globally important crops. J Agric Meteor Jpn 60:469–474.

Burns WC. 2002. Climate change and human health: the critical policy agenda. JAMA 287:2287.

Canadell JG, Le Quere C, Raupach MR, Field CB, Buitenhuis ET, Clais P, et al. 2007. Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks. Proc Natl Acad Sci USA 104:18866–18870.

Emberlin J, Detandt M, Gehrig R, Jager S, Nolard N, Rantio-Lehtimaki A. 2002. Responses in the start of Betula (birch) pollen seasons to recent changes in spring temperatures across Europe. Int J Biometeor 46:159–170.

Epstein PR. 2005. Climate change and human health. New Engl J Med 353:1433–1436.

Epstein PR, Mills E, editors. 2005. Climate Change Futures: Health, Ecological and Economic Dimensions, Center for Health and the Global Environment. Boston, MA:Harvard Medical School. Available:​CCF_Report_Final_10.27.pdf [accessed 4 August 2008].

Farnsworth NR, Akerele O, Bingel AS, Soejarto DD, Guo Z. 1985. Medicinal plants in therapy. Bull WHO 63:965–981.

Gamble JL, Ebi KL, Sussman FG, Wilbanks TJ, editors. 2008. Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems. Washington DC:U.S. Environmental Protection Agency.

Gergen PJ, Turkeltaub PC, Kovar MC. 1987. The prevalence of allergic skin test reactivity to eight common aeroallergens in the US population: results from the second National Health and Nutrition Examination survey. J Allergy Clin Immunol 80:669–679.

Hatfield J. 2008. Agriculture. In: The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States (Backlund P, Janetos A, Schimel D, eds.). Synthesis and Assessment Product 4.3. Washington, DC:U.S. Climate Change Science Program, 21–74.

Hesman T. 2002. Carbon dioxide spells indigestion for food chains. Sci News 157:200–202.

Horie T, Baker JT, Nakagawa H, Matsui T, Kim HY. 2000. Crop ecosystem responses to climatic change: rice. In: Climate Change and Global Crop Productivity (Reddy KR, Hodges HF, eds.). New York:CABI Press, 81–106.

Idso KE, Idso SB. 1994. Plant responses to atmospheric CO2 enrichment in the face of environmental constraints—a review of the past 10 years research. Agric For Meteorol 69:153–203.

IPCC (Intergovernmental Panel on Climate Change). 2007. Climate Change 2007: Impacts, Adaptation and Vulnerability. Geneva:IPCC Secretariat.

Kerr RA. 2007. Global warming coming home to roost in the American West. Science 318:1859.

Kimball BA. 1993. Effects of increasing atmospheric CO2 on vegetation. Vegetatio 104/105:65–75.

Kimball BA, Morris CF, Pinter PJ Jr, Wall GW, Hunsaker DJ, Adamsen FJ, et al. 2001. Elevated CO2, drought and soil nitrogen effects on wheat grain quality. New Phytol 150:295–303.

Klironomos JN, Allen MF, Rillig MC, Zak DR, Pregitzer KS, Kubiske ME. 1997. Increased levels of airborne fungal spores in response to Populus tremuloides grown under elevated atmospheric CO2. Can J Bot 75:1670–1673.

LaDeau SL, Clark JS. 2006. Pollen production by Pinus taeda growing in elevated atmospheric CO2. Funct Ecol 10:1365–1371.

Long SP. 1991. Modification of the response of photosynthetic productivity to rising temperature by atmospheric CO2 concentrations: has its importance been underestimated? Plant Cell Environ 14:729–739.

McMichael AJ, Woodruff RE, Hales S. 2006. Climate change and human health: present and future risks. Lancet 368:859–869.

Mohan JE, Ziska LH, Schlesinger WH, Thomas RB, Sicher RC, George K, et al. 2006. Biomass and toxicity responses of poison ivy (Toxicodendron radicans) to elevated atmospheric CO2. Proc Natl Acad Sci USA 103:9086–9089.

Patterson DT. 1995. Weeds in a changing climate. Weed Sci 43:685–701.

Patz JA, Kovats RS. 2002. Hot spots in climate change and human health. Br Med J 325:1094–1098.

Pimentel D. 1997. Techniques for Reducing Pesticides: Environmental and Economic Benefits. Chichester, UK:John Wiley and Sons.

Pitman N, Jorgensen P. 2002. Estimating the size of the world’s threatened flora. Science 298:989.

Poorter H. 1993. Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration. Vegetatio 104/105:77–97.

Prasad PVV, Boote KJ, Allen LH Jr. 2006. Adverse high temperature effects on pollen viability, seed-set, seed yield and harvest index of grain-sorghum [Sorghum bicolor (L.) Moench] are more severe at elevated carbon dioxide due to higher tissue temperatures. Agric For Meteorol 139:237–251.

Rogers CA, Wayne PM, Macklin EA, Mullenberg ML, Wagner CJ, Epstein PR, et al. 2006. Interaction of the onset of spring and elevated atmospheric CO2 on ragweed (Ambrosia artemisiifolia L.) pollen production. Environ Health Perspect 114:865–869.

Rogers GS, Gras PW, Batey IL, Milham PJ, Payne L, Conroy JP. 1998. The influence of atmospheric CO2 concentration on the protein, starch and mixing properties of wheat flour. Aust J Plant Physiol 25:387–393.

Singer BD, Ziska LH, Frenz DA, Gebhard DE, Straka JG. 2005. Increasing Amb a 1 content in common ragweed (Ambrosia artemisiifolia) pollen as a function of rising atmospheric CO2 concentration. Funct Plant Biol 32:667–670.

Stuhlfauth T, Fock HP. 1990. Effect of whole season CO2 enrichment on the cultivation of a medicinal plant, Digitalis lanata. J Agron Crop Sci 164:168–173.

Trotter WR. 1990. Is bracken a health hazard? Lancet 336:1563–1565.

Wan S, Yuan T, Bowdish S, Wallace L, Russell SD, Luo Y. 2002. Response of an allergenic species, Ambrosia psilostachya (Asteraceae), to experimental warming and clipping: implications for public health. Am J Bot 89:1843–1846.

Wang SY, Bunce JA, Maas JL. 2003. Elevated carbon dioxide increases contents of antioxidant compounds in field-grown strawberries. J Agric Food Chem 51:4315–4320.

Watson WA, Litovitz TL, Klein-Schwartz W, Rodgers GC, Youniss J, Reid N, et al. 2004. 2003 Annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am J Emer Med 22:335–404.

Wayne P, Foster S, Connolly J, Bazzaz FA, Epstein PR. 2002. Production of allergenic pollen by ragweed (Ambrosia artemisiifolia L.) is increased in CO2-enriched atmospheres. Ann Allergy Asthma Immunol 80:669–679.

WHO (World Health Organization). 2002. Traditional medicine: growing needs and potential WHO Policy. Perspect 2:1–6.

Ye-Ebiyo Y, Pollack RJ, Spielman A. 2000. Enhanced development in nature of larval Anopheles arabiensis mosquitoes feeding on maize pollen. Am J Trop Med Hyg 63:90–93.

Ziska LH, Caulfield FA. 2000. Rising carbon dioxide and pollen production of common ragweed, a known allergy-inducing species: implications for public health. Aust J Plant Physiol 27:893–898.

Ziska LH, Emche SD, Johnson EL, George K, Reed DR, Sicher RC. 2005. Alterations in the production and concentration of selected alkaloids as a function of rising atmospheric carbon dioxide and air temperature: implications for ethno-pharmacology. Global Change Biol 11:1798–1807.

Ziska LH, Epstein PR, Rogers CA. 2008a. Climate change, aerobiology and public health in the Northeast United States. Mitig Adapt Strat Glob Change 13:607–613.

Ziska LH, Faulkner SS, Lydon J. 2004. Changes in biomass and root:shoot ratio of field-grown Canada thistle (Cirsium arvense), a noxious, invasive weed, with elevated CO2: implications for control with glyphosate. Weed Sci 52:584–588.

Ziska LH, Gebhard DE, Frenz DA, Faulkner S, Singer BD. 2003. Cities as harbingers of climate change: common ragweed, urbanization, and public health. J Allergy Clin Immunol 111:290–295.

Ziska LH, Namuco OS, Moya TB, Quilang JPE. 1997. Growth and yield response of field-grown tropical rice to increasing CO2 and air temperature. Agron J 89:45–53.

Ziska LH, Palowsky R, Reed DR. 2007. A quantitative and qualitative assessment of mung bean (Vigna mungo (L.) Wilczek) seed in response to elevated atmospheric carbon dioxide: potential changes in fatty acid composition. J Sci Food Agric 87:920–923.

Ziska LH, Panicker S, Wojno HL. 2008b. Recent and projected increases in atmospheric carbon dioxide and the potential impacts on growth and alkaloid production in wild poppy (Papaver setigerum DC.). Clim Change 91:395–403.

Ziska LH, Runion GB. 2007. Future weed, pest and disease problems for plants. In: Agroecosystems in a Changing Climate (Newton PCD, Carran A, Edwards GR, Niklaus PA, eds.). Boston, MA:CRC Press, 262–279.

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