Merkel cell carcinoma, the skin cancer that killed beloved Margaritaville singer Jimmy Buffett on September 1, is rare. But it may become more common in the coming decades. Every year the US diagnoses 3,000 new cases of this disease—a number that is estimated to increase to 3,250 cases by 2025. As the US population ages and global warming influences ultraviolet radiation, dermatologists suspect this caseload will only continue to get higher.
“We know that Merkel cell carcinoma occurs in sun-exposed areas and that UV, in particular, is a risk factor,” says Eva Parker, an assistant professor of dermatology at Vanderbilt University Medical Center who has studied climate change’s impact on skin cancer. “I believe we will continue to see increasing rates of both common and less common types of skin cancer.” She pointed to two contributing trends: the delayed period over which skin cancer develops, plus the growing effects of climate change that includes continued pressure humans are placing on the protective ozone layer in the stratosphere.
The relationship between climate change and skin cancer is complex. On one hand, ultraviolet radiation from the sun contributes to skin cancer, because this light can damage our cells’ DNA. And ultraviolet radiation exists regardless of climate change.
On the other hand, there’s circumstantial evidence that factors related to climate change—stratospheric ozone depletion, heat, and air pollution—are likely contributing to the increasing incidence for melanoma and non-melanoma skin cancer. (Fast-growing Merkel cell carcinomas are a subtype of non-melanoma skin cancer.) Research suggests an average global warming of 3.6 degrees Fahrenheit is associated with an 11 percent rise in all skin cancers worldwide. The world is already on track to reach this number by 2050.
[Related: Why doctors almost never say cancer is ‘cured’]
The problem with establishing a direct link to climate change and increasing skin cancer cases is that most of the data is based on animal studies and computer modeling. To definitively say that climate change causes skin cancer, Parker says more epidemiological data on humans is needed. Though she explains how climate change may directly or indirectly contribute to rising skin cancer cases.
One reason is likely because of stratospheric ozone depletion. Think of the ozone layer as a giant hat that covers Earth and blocks out ultraviolet and UVB radiation, which is associated with many forms of skin cancer including Merkel cell carcinoma. In the 1970s, scientists started noticing holes in the ozone layer. Further investigation showed that artificial compounds such as chlorofluorocarbons were destroying ozone. “They’re potent greenhouse gases and incredibly long-lived in the atmosphere,” explains Parker. “The implication is that stratospheric ozone depletion will be ongoing for many decades, even though chlorofluorocarbons have been regulated for some time.”
With less ozone absorbing UVB radiation, people are more exposed to the radiation’s damaging effects on skin cells, leading to an increasing risk of skin cancer. Fortunately, phasing ozone-depleting chemicals has helped to repair this layer, though the healing process has been slow. Environmental scientists estimate it will take until 2040 for ozone to return to the levels they were in the 1980s.
[Related: Wind turbines do not cause cancer]
Missing ozone is one climate-related contributor to skin cancer. Heat is another possible culprit, Parker says. Ultraviolet radiation needs heat to activate its tumor-forming ability. Excess heat could indirectly create an ideal environment for cancer to flourish. And, when combined with high humidity, it messes with the body’s way of regulating body temperature. When a body can’t cool itself down through sweating, this could lead to physiological dysfunctions, including issues with gene expression while increasing inflammation and oxidative stress. Lastly, when it’s hot outside, people usually wear less clothing, which heightens their UV exposure and skin cancer risk.
There is one silver lining: While Merkel cell carcinoma is more aggressive than melanoma, it is curable if caught early and treated successfully, says Ling Gao, an associate professor of dermatology at the University of California, Irvine. “For all skin cancers, early diagnosis greatly improves outcomes.”
You’re better off, though, by preventing skin cancer from appearing altogether. The first step is to identify when you’re most exposed to the sun, says David Leffell, a professor of dermatology at Yale School of Medicine and a fellow of the American Academy of Dermatology. Next, you’ll want to take steps to minimize that exposure. If you often go for a 15-minute walk around the block, stay in the shade and avoid peak hours like noon when the sun is at the highest point in the sky. When you do go outside, shield yourself from ultraviolet rays with SPF 50 sunscreen. What you wear helps, too: A brimmed hat and specialized clothing, such as UPF rated shirts and pants, can block out the sun’s rays.
If you’re unsure whether you should go outside today, consider downloading an app that rates the UV index. Similar to checking weather forecasts, a UV index will tell you whether it’s safer to stay indoors or to pack some sunscreen before heading out.