A Complex Web of Factors Causes Climate Change to Increase the Risk and Burden of Skin Cancer

Skin cancer is one of the most common diseases dermatologists deal with on a daily basis, and as rates increase, it is clear that climate change is a contributory factor, according to Eva R. Parker, MD, FAAD, assistant professor of dermatology, Vanderbilt University Medical Center.

During her session at the American Academy of Dermatology Virtual Meeting Experience, she highlighted the 3 main ways climate change and environmental effects are contributing to rising skin cancer rates: stratospheric ozone depletion, heat due to global warming, and air pollution.

The United States has more than 5 million cases of skin cancer annually, and there has been a steady upward trend in melanoma incidence. The trend also has been seen globally, especially among fair-skinned populations, with melanoma rates increasing 4% to 5% annually.

In the United States, skin cancer treatment costs top $8 billion annually. In addition to being a huge economic burden, the disease diminishes quality of life and carries with it notable morbidity, disability, and mortality, she said.

“I really don’t need to tell a group of dermatologists that the sun causes skin cancer, but it is noteworthy to remind the audience that UV [ultraviolet] is a complete carcinogen, meaning it causes mutations that lead to skin cancer without the need for additional promoters or initiators,” Parker explained.

She called the stratospheric ozone Earth’s “broad-brimmed hat” that is essential to blocking out UVC rays. There are 3 types of UV rays:

• UVA has the longest wavelength and penetrates deeper into the skin. This makes up the majority (90%-95%) of sunlight reaching Earth’s surface.
• UVB rays come into contact with the outer layer of skin. Significantly less (5%-10%) UVB rays reach the Earth’s surface.
• UVC has the shortest wavelengths and is mostly absorbed by the ozone. These are the strongest rays.

Large holes in the ozone layer were first discovered in 1985 with Antarctica having the largest hole, which at times has been 3 times the size of the United States. As a result of these holes, UV radiation is most pronounced in the southern hemisphere and high latitudes. Melbourne, Australia, which is at 38 degrees south latitude, received 10% more UVB as a result of ozone depletion. In comparison, Nashville, Tennessee, which is at 36 degrees north latitude, is receiving 6% to 7% more UVB rays.

A 10% reduction in stratospheric ozone will cause an estimated 300,000 additional skin cancer cases, Parker said. As more UVB rays reach the surface, they will cause more DNA damage and skin cancer.

In 1987, the Montreal Protocol was universally ratified. It is a global agreement to protect the stratospheric ozone by phasing out the production and consumption of ozone-depleting substances.

“Arguably the Montreal Protocol has been a tremendous success, as it is estimated to have already prevented over 20 million cases of skin cancer and will continue to prevent an additional 2 million cases of skin cancer globally per year over the next decade,” Parker said.

The Montreal Protocol was also expected to recover the ozone layer over Antarctica by 2060; however, it is becoming clear that prior modeling may not have been entirely accurate, she said. While ozone density is slowly improving at the poles, it has actually worsened at mid-latitudes, which is particularly concerning since these latitudes are the most densely populated regions of the world.

One of the big reasons the protocol is not on track is because of climate change, Parker explained. Researchers are just beginning to understand how stratospheric ozone concentrations and climate change impact one another.

“It is now thought that climate change forces may delay ozone recovery by 30 years, which is not good news for the future of skin cancer,” she said.

Shifting gears to climate change, Parker pointed out that the planet is experiencing a major shift to hotter weather, as evidenced by the fact that the last 6 years were the hottest on record ever. Importantly, people behave differently when the weather is hot: They spend more time outdoors and wear less clothing, thus exposing them more to UV radiation.

Heat also has an impact on carcinogenesis, and past research has shown that not only is UV radiation more effective at creating tumors at higher temperatures, but that nonmelanoma skin cancer risk increases for every Celsius degree of temperature increase.

“That means that as the planet continues to warm, there’s the possibility that rising temperatures could amplify the induction of skin cancer by UV radiation, further driving increased rates of skin cancer,” she said.

Finally, while air pollution is frequently thought of as a respiratory issue, it also has implications for skin cancer as some particulate matter, an important indicator of air quality, not only penetrates the lungs but also enters systemic circulation, crosses the blood-brain barrier, and can even penetrate the epidermis directly. The impact of air pollution on skin cancer risk is beginning to be better understood, Parker said.

Australia, and its neighbor New Zealand, should be viewed as cautionary tales for the rest of the world, Parker said in conclusion. The country is a mostly fair-skinned population with a sun-centric culture. As a subtropic latitude in the southern hemisphere, the country is particularly affected by stratospheric ozone depletion, and in recent years Australia has seen record heat waves, droughts, and wildfires. Australia and New Zealand have the highest rates of cutaneous malignancy, and these rates have been rising.

“Australia is a perfect storm and is illustrative of how climate change is affecting skin cancer rates,” Parker said.

Some populations will be more vulnerable to the risk of skin cancer as a result of climate change, she pointed out. For instance, certain comorbid conditions, such as albinism and vitiligo, will increase the risk. Outdoor workers and those who live at higher altitudes are at greater risk, and because limited access to health care and systemic racism play roles in vulnerability, skin cancer risk as a result of climate change will disproportionately affect skin of color, indigenous populations, and the poor, she said.

According to Parker, the dermatology audience had an obligation to make climate change research a priority and needed to be advocates for drastic changes to mitigate the health effects.

“Because the human population has doubled in last 50 years, the critical pressures of climate change act as force multipliers, increasingly magnifying the health impact of those pressures,” she said. “We are at a crucial crossroads: our next move will be enormously consequential leading many to consider climate change to be the existential crisis of this century.”