Global climate appears to be changing at an unprecedented rate. Climate change can be caused by many factors, including variations in solar radiation received by the earth, oceanic circulation, plate tectonics, as well as human-induced alterations of the natural world. Many human activities, such as the use of fossil fuel and the consequent accumulation of greenhouse gases in the atmosphere, land consumption, deforestation, industrial processes, as well as some agriculture practices, are contributing to global climate change. Many have reported on the current trend toward global warming (average surface temperature has augmented by 0.6°C over the past 100 years), decreased precipitation, atmospheric humidity changes, and the rise in global extreme climatic events. The magnitude and cause of these changes and their impact on human activity have become important matters of debate worldwide, representing climate change as one of the greatest challenges of the modern age.
Although many articles have been written based on observations and various predictive models of how climate change could affect social, economic, and health systems, only a few studies exist about the effects of this change on skin and skin disease. However, the skin is the most highly exposed organ to the environment; therefore, cutaneous conditions are inclined to respond to changes in climate.
The World Health Organization predicts that the depletion of the ozone layer could lead to further increased rates of melanoma and nonmelanoma skin cancer. In humans, it has been speculated that a long-term rise of temperature by 2°C could increase the carcinogenic effectiveness of solar UV by 10%.
Strictly speaking, stratospheric ozone depletion is not part of “global climate change,” which occurs in the troposphere. There are, however, several recently described interactions between ozone depletion and greenhouse gas–induced warming. Stratospheric ozone absorbs much of the incoming solar ultraviolet radiation, especially the biologically more damaging, shorter-wavelength UVB wavelengths. We now know that various industrial halogenated chemicals such as the chlorofluorocarbons or CFCs (used in refrigeration, insulation, and spray-can propellants) and methyl bromide, while inert at ambient Earth-surface temperatures, react with ozone in the extremely cold polar stratosphere. This destruction of ozone occurs especially in late winter and early spring.
During the 1980s and 1990s at northern midlatitudes (such as Europe), the average year-round ozone concentration declined by around 4% per decade; over the southern regions of Australia, New Zealand, Argentina, and South Africa, the figure approximated 6%-7%. UV exposures at northern midlatitudes are likely to peak around 2020, with an estimated 10% increase in effective ultraviolet radiation relative to 1980s levels.
The modeling of future ozone levels and UV radiation (UVR) exposures has estimated that, in consequence, a ‘European’ population living at around 45 degrees North will experience, by 2050, an approximate 5% excess of total skin cancer incidence (assuming, conservatively, no change in age distribution). The equivalent estimation for the U.S. population is for a 10% increase in skin cancer incidence by around 2050.
In the mid-1980s, governments recognized the emerging hazard from ozone depletion. The Montreal Protocol of 1987 was adopted, and the phasing out of major ozone-destroying gases began. Some anticipate a slow but near-complete recovery of stratospheric ozone by the middle of the twenty-first century; the Environmental Protection Agency (EPA) estimates recovery by 2065 with strict adherence to protection protocols.
Increased exposure to UVR also leads to increased rates of lens opacification, cataracts, and whole-body immunosuppression. UVR-induced immunosuppression could influence patterns of infectious disease. It may also influence the occurrence and progression of various autoimmune diseases and, less certainly, vaccine efficacy.
Extreme weather events
The International Society of Dermatology Task Force on Climate Change reports that weather phenomena such as El Niño also result in changes to dermatologic conditions. The El Niño Southern Oscillation ( ENSO ) is a complex climate phenomenon occurring in the Pacific Ocean at intervals of 2-7 years. The term refers to fluctuations in ocean temperatures in the tropical eastern Pacific Ocean (El Niño, the warm phase of ENSO, and La Niña, the cool phase of ENSO) and in atmospheric pressure across the Pacific basin (Southern Oscillation). This weather pattern is attributed with causing climate change in certain parts of the world and is associated with disease outbreaks.
El Niño has been associated with increases in the occurrence of actinic keratosis, tinea, pityriasis versicolor, miliaria, folliculitis, rosacea, dermatitis caused by Paederus irritans and Paederus sabaeus, and certain vector-borne and waterborne diseases (such as dengue fever, leishmaniasis, Chagas disease , Barmah Forest virus , and leptospirosis ), and with decreases in the occurrence of dermatitis, scabies, psoriasis, and papular urticaria. La Niña has been associated with increases in the occurrence of varicella; hand, foot, and mouth disease; and Ross River virus (in certain areas), and decreases in viral warts and leishmaniasis.
Separately, global warming is expected to affect the start, duration, and intensity of the pollen season, and secondarily the rate of asthma exacerbations due to air pollution, respiratory infections, and/or cold air inhalation, with probable increases in eczema and other atopy-related conditions as well.
In the past year, the largest Ebola virus outbreak in West Africa has resulted in importation of the virus to other countries and secondary local transmission. Autochthonous transmission of Chikungunya virus has occurred in nonendemic areas, including Europe, the Caribbean, and the Americas. Zika virus has re-emerged in the Pacific with local transmission from imported cases. Climate change, deforestation, and changes in precipitation have been linked to variations in the geographical distribution of vectors of some infectious diseases (leishmaniasis, Lyme disease, and now Zika virus) by changing their spread. A warm and humid environment from global warming can also encourage the colonization of the skin by bacteria and fungi.
Finally, there is a wider, ecological dimension to consider. UV radiation impairs the molecular chemistry of photosynthesis both on land (terrestrial plants) and at sea (phytoplankton). This could affect world food production, at least marginally, and thus contribute to nutritional and health problems in food-insecure populations.
Another reason of many, but from a dermatologist’s point of view, to be mindful of taking care of the planet and our environment.
1. World Health Organization ( WHO ).
Dr. Wesley and Dr. Talakoub are co-contributors to this column. Dr. Talakoub is in private practice in McLean, Va. Dr. Wesley practices dermatology in Beverly Hills, Calif. This month’s column is by Dr. Wesley. Write to them at firstname.lastname@example.org .