Global warming and its dermatologic impact

Keywords::

• climate change
• dermatology
• disease vectors
• global warming
• UV radiation

Global surface temperatures rose 0.74 ± 0.18°C during the last century [1]. The last 50 years witnessed almost double the rate of warming of the last 100 years. Over the next century, temperatures are projected to rise several degrees further, depending on the model of climate change followed. While the myriad consequences of global warming are predicted to affect virtually all walks of life, several aspects pose particular challenges for dermatology. Progress on meeting them continues to build.

Climate changes

Evidence points to a causal role for anthropogenic carbon emissions in the context of global warming. Carbon dioxide and other greenhouse gases such as methane trap solar infrared radiation. The increase in atmospheric concentration of carbon dioxide has been attributed to human activities such as burning fossil fuels and deforestation. This rising concentration is thought to be the culprit behind the changes in global surface temperatures.

Some of the consequences of this change in global climates may include increased exposure to ultraviolet radiation, a greater severity of extreme weather events and new patterns of disease vectors.

UV effects

Efforts have been made over the years to raise public awareness of the effects of UV radiation. Concerns have focused on depletion of the ozone layer, as well as social trends such as sunbathing and tanning parlors, but climate change may also affect levels of UV exposure. In addition, rising temperatures may increase the carcinogenic effectiveness of UV radiation. As early as the mid-20th Century, studies on mice showed that elevated temperatures enhanced UV-induced carcinogenesis. Studies of humans suggest similar effects, with each °C rise corresponding to an estimated equivalent impact of +2% in effective UV dose [2].

Such effects will be intertwined with those of changing social patterns, from growth in outdoor leisure activities to countervailing trends to remain indoors. Humans have always had a large say in the matter of their own health. But even human behavior, especially in an age of anthropogenic climate change, may prove the greatest determinant of outcomes. Behavior associated with climate change, as Diffey proposed for the UK population [3,4], may have a larger impact on UV exposure and consequent skin cancer than ozone depletion. In other regions, climate change may compel people to limit their outdoor activities, as predicted by Maloney and Forbes [5] in Australia, increasing the number of days unsuitable for labor or strenuous exercise.

Extreme weather events

Recent years have witnessed many natural disasters, from the Indian Ocean tsunami, to Hurricane Katrina, to the floods in Pakistan and the Mississippi River basin, as well as others too numerous to list. While individually their links to climate change are difficult to parse, collectively they illustrate the impending challenges society and health professionals face from changing weather patterns.

The spread of natural disasters has changed the literature on skin infections. After Hurricane Katrina in 2005, the CDC reported on wound infections with methicillin-resistant Staphylococcus aureus (MRSA), Vibrio vulnificus and Vibrio parahaemolyticus among local residents, and tineacorporis, folliculitis, miliaria and arthropod bites among rescue personnel [6]. Rhoads also reported on cases of V. vulnificus causing problems, including septic shock, for victims [7].

The Indian Ocean tsunami of December 2004 provided the literature with new cases of dermatologic conditions associated with massive flooding. Multidrug-resistant diseases, polymicrobial infections and other unusual pathogens, such as Burkholderia pseudomallei, Cladophialophora bantiana and Mycobacterium abscessus, were found following exposure to freshwater contaminated by flooding [8–10]. In another report, Hiransuthikul et al. found that 515 (66.3%) tsunami survivors with traumatic wounds were diagnosed with skin and soft-tissue infections, with the most common isolated being Aeromonas species [11]. Such challenges may become more familiar to dermatologists if these weather trends continue.

Habitats & disease vectors

Environmental changes wrought by global warming may alter the patterns of diseases and outbreaks. There will be many factors influencing these changes in disease dynamics, such as globalization and demographic shifts; climate change may prove one of the largest.

As climates warm, diseases previously confined to lowlands and the tropics may move into higher elevations and more northern latitudes [12]. An example among animals is the fate of the Monteverde harlequin frog (Atelopus spp.), which fell extinct after an outbreak of the pathogenic chytrid fungus Batrachochytrium, which had expanded its range into the highlands after temperatures warmed [13]. Humans may be susceptible to similar outbreaks as Staphylococcus, Streptococcus and enteric bacteria, for example, fare better in warmer climes [14,15]. McBride et al. found that high temperatures and humidity increased the overall frequency of isolation of Gram-negative bacteria, though with individual differences [16]. Treating outbreaks of such diseases, potentially resistant to antimicrobials, will be a test for dermatologists.

Various authors have explored the potential effects of climate change upon vector-borne diseases such as malaria, dengue, leishmaniasis and tick-borne diseases [17–20]. As an example of the relationships between vector-borne diseases and climate variation, Cárdenas et al.[21] report on the impact of the El Nino Southern Oscillation on the incidences of leishmaniasis in Columbia from 1985 to 2002, which show an increase during El Nino and decrease during La Nina phases [16]. However, the existing literature may not present sufficient evidence to support a casual relationship between global warming and increased incidence for all vector-borne diseases; in the case of tick-borne diseases, Randolph argued that climate change had not been proven to be the cause of the increases in such cases, despite the susceptibility of such systems to climate changes [22]. As is often the case, more research is necessary; what distinguishes climate change is the impact knowlede may have.

Challenges & skin bacteriology

Adapting to the demands of climate change appears an increasingly imposing task. It seems likely that our existing arsenal of tools will require bolstering. Dermatology will need to advance to meet the challenge of treating the largest human organ, in knowledge and practice.

For example, the skin, like the GI tract, is heavily colonized. Recently, dermatologists have learned to appreciate the complexity of this biota and improve their investigations [23]. Such new molecular identification tools, still in their infancy, should provide fertile insights into the role of microbes in health and disease. The implications as they relate to climate control mandate detailed investigation.

Contemplating the future

Considering the breadth of these tasks, their solutions demand collective action (Table 1). With millions of species potentially facing extinction, the challenges facing scientists and modern medicine over the next century are a serious matter [24]. Acknowledgement of the challenges posed has been growing among health professionals [25–28].

Dermatologists will need every tool at their disposal to face the task of caring for patients and preparing society for the coming demands.

Table 1. Potential dermatologic consequences of climate change.

	Changes	Effects	Ref.
Physical	Rise of several degrees Celsius, greater UV exposure	Higher incidence of skin cancer	[1,2]
Weather	Higher frequency and severity of tropical storms, more flooding	More cases of skin infection	[6–11]
Environment	Shifting biomes	Expanded range of tropical diseases, altered patterns of disease vectors	[12,13,16,18–22,24,25]

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.