UV radiation reaching Earth’s surface has broadly increased since the late 1970s, driven primarily by thinning of the ozone layer during the decades before international action began reversing the damage. Satellite data covering 1979 to 2008 show significant increases at nearly all latitudes outside the tropics, with the largest jumps in the Southern Hemisphere. But the story is far from a simple upward line. Clouds, air pollution, snow cover, wildfire smoke, and the sun’s own cycles all push surface UV up or down depending on where and when you measure, making “are UV rays getting stronger” a question with a different answer depending on your zip code.
What the Satellite Record Shows
The clearest long-term picture comes from instruments aboard satellites that have been measuring both ozone and surface reflectivity since the late 1970s. An analysis joining multiple satellite datasets from 1979 to 2008 found that surface UV irradiance increased significantly at all latitudes except a narrow band around the equator, with the Southern Hemisphere seeing the biggest jumps. The increase tracked closely with ozone losses measured over the same period.1Journal of Geophysical Research: Atmospheres. Global increase in UV irradiance during the past 30 years (1979–2008) estimated from satellite data A separate satellite-based study using erythemal UV products (a measure weighted toward the wavelengths that burn human skin) found positive changes ranging from 0 to about 5% per decade, with the strongest increases at southern midlatitudes during spring and summer, right where ozone depletion had been worst.2Atmospheric Chemistry and Physics. Use of satellite erythemal UV products in analysing the global UV changes
A more recent global assessment extending through 2023 added nuance. Both the global median and mean UV radiation declined from 1940 to 1980. After 1980, the median rose significantly, but the mean barely changed, which tells us something important: some regions saw large increases that pulled the median up, while other regions saw decreases that dragged the mean back down. From 1990 to 2021, the rising median reflected an overall yearly increase across most of the world, but there were pockets going the opposite direction.3PubMed Central. Global assessment of surface ultraviolet radiation and malignant skin melanoma incidence from 1990 to 2021
That divergence between median and mean is a clue that the forces driving UV changes are not uniform. The answer to whether UV is getting stronger depends heavily on what part of the planet you are standing on and what is happening in the atmosphere above you.
The Ozone Layer and Its Slow Recovery
The dominant reason surface UV climbed in the 1980s and 1990s is straightforward: the ozone layer was thinning. Ozone in the stratosphere absorbs UV-B radiation before it reaches the ground, so less ozone means more UV. The cause of that thinning, chlorofluorocarbons and other halogenated chemicals, was addressed by the Montreal Protocol, signed in 1987. And the protocol has worked. A 2022 analysis of five merged ozone datasets found that total ozone is slowly recovering in both hemispheres, with the near-global recovery trend running at roughly 0.4% per decade after 1995. That recovery rate is about a third of the rate at which ozone was declining before 1995, and the ratio matches the change in stratospheric halogen concentrations, confirming that the treaty is doing what it was designed to do.4Atmospheric Chemistry and Physics. Global total ozone recovery trends attributed to ozone-depleting substance (ODS) changes derived from five merged ozone datasets
Modeling work drives home how much worse things could have gotten. Without the Montreal Protocol’s actions, ozone could have been almost entirely depleted by the end of this century, with continuous increases in stratospheric halogens destroying roughly 80% of the total ozone column.5Atmospheric Chemistry and Physics. Montreal Protocol’s impact on the ozone layer and climate In that counterfactual world, UV levels at the surface would have been catastrophic. Instead, ozone is on a slow upward track, which means the primary driver of rising UV is gradually weakening.
There is an unexpected helper in this recovery. Rising greenhouse gas concentrations cool the stratosphere even as they warm the surface. That cooling weakens the chemical cycles that destroy ozone, effectively giving ozone a boost. One study estimated that up to the year 2000, cooling from increased CO₂ offset roughly 25% of the ozone loss that would otherwise have occurred from ozone-depleting substances. Looking forward, as those substances decline, continued CO₂-driven cooling is projected to account for more than half the increase in upper-stratospheric ozone over the 21st century.6Atmospheric Chemistry and Physics. Quantifying the contributions to stratospheric ozone changes from ozone depleting substances and greenhouse gases In some models, this effect pushes ozone in the upper stratosphere back to 1980 or even 1960 levels several decades before halogen concentrations have fully returned to pre-industrial values.7Geophysical Research Letters. Impacts of climate change on stratospheric ozone recovery
How Much Does the Sun Itself Change
Because UV radiation originates from the sun, a natural question is whether the sun is simply putting out more of it. The sun’s UV output does fluctuate, but on an 11-year cycle tied to sunspot activity, not a long-term upward trend.8Physics Open. Comparison between variations in solar UV radiation and sunspot parameters with Mg II daily index as a proxy Reconstructions of how much UV changes across a full solar cycle show that radiation in the 200 to 300 nm band (which includes the biologically potent UV-B and UV-C wavelengths) varies by about 1.1% from solar minimum to solar maximum. In the 300 to 400 nm band (UV-A, the stuff that tans and ages skin), the swing is much smaller, roughly 0.25%.9Journal of Geophysical Research: Atmospheres. Detection and parameterization of variations in solar mid‐ and near‐ultraviolet radiation (200–400 nm)
Those swings are real, but they are cyclical, not directional. There is no evidence that the sun’s UV output is trending upward over decades. The 11-year cycle can make UV measurements noisy if you are comparing two years that happen to fall on opposite ends of a solar cycle, which is one reason long datasets are so important. But the sun is not the reason your dermatologist is concerned.
Clouds, Pollution, and the Atmosphere Below the Ozone
Ozone dominates the UV story at high latitudes and during the spring, but at low and middle latitudes, the atmosphere between the stratosphere and the ground matters just as much, sometimes more. A comprehensive review found that changes in UV radiation between roughly 0° and 60° latitude over the past 25 years have generally been small, typically less than 4% per decade, and at many ground stations the direction was inconsistent: some sites saw increases, others decreases. The primary drivers were changes in cloud cover and atmospheric aerosol content rather than ozone.10PubMed Central. Stratospheric ozone, UV radiation, and climate interactions
This means that in polluted industrial regions, heavy aerosol loads can actually suppress surface UV, masking whatever increase ozone changes might otherwise deliver. Delhi is a dramatic example. Satellite-derived UV data over 17 years showed UV-A declining by about 10% and UV-B declining by about 20% relative to their means, tracking directly with rising aerosol loads.11Atmospheric Environment. Assessment of satellite-retrieved surface UVA and UVB radiation by comparison with ground-measurements and trends over Mega-city Delhi If India and China continue cleaning up their air quality (as international pressure and domestic policy both push), UV at the surface in those regions will rebound toward pre-pollution levels. The same review noted this explicitly: in regions currently affected by air pollution, UV radiation will increase as anti-pollution measures gradually restore UV intensities to those of a cleaner atmosphere.10PubMed Central. Stratospheric ozone, UV radiation, and climate interactions
Clouds add another layer of complexity. Climate models project that changes in cloud cover at high northern latitudes could reduce yearly average erythemal UV by around 5% relative to 1960s levels by the end of this century, while at midlatitudes clouds slightly moderate the decrease from ozone recovery, effectively keeping UV a touch higher than it would otherwise be.12Atmospheric Chemistry and Physics. Projections of UV radiation changes in the 21st century: impact of ozone recovery and cloud effects In other words, cloud trends can either amplify or counteract ozone-driven UV changes depending on where you live.
Wildfire Smoke and Volcanic Eruptions
Beyond the gradual trends, punctuated events can dramatically alter UV levels in ways that catch atmospheric scientists off guard. Australia’s “Black Summer” fires in 2019–2020 injected enormous quantities of smoke directly into the stratosphere, where the particles triggered chemical reactions that destroyed ozone. Satellite instruments recorded extreme perturbations in stratospheric chemistry, including increases in chlorine compounds that actively consume ozone, far beyond anything seen in the previous 15 years of monitoring.13PubMed. Wildfire smoke destroys stratospheric ozone As wildfire seasons intensify with climate change, this mechanism could produce temporary spikes in surface UV over regions downwind of major burns.
Large volcanic eruptions can have even more extreme effects. Modeling of tropical volcanic eruptions of the magnitude seen in pre-industrial times showed that global clear-sky UV-B could increase by a maximum of 80% in the tropics, with increases exceeding 190% at northern midlatitudes and surpassing 400% during peak Antarctic ozone depletion.14Scientific Reports. Global ozone depletion and increase of UV radiation caused by pre-industrial tropical volcanic eruptions These are extreme, short-lived events, not part of a long-term trend, but they illustrate how quickly and severely the UV environment can shift.
At a more regional scale, fragments of ozone-depleted air from the Antarctic polar vortex occasionally break off and drift over populated midlatitude areas like southern Brazil, temporarily thinning ozone overhead and allowing more UV through.15EGUsphere. UV solar radiation climatology and its behaviour during events of influence of the Antarctic ozone hole over south of Brazil If you happen to be outside during one of these events, you are effectively getting an Antarctic ozone hole’s worth of UV exposure at a latitude where nobody expects it.
Why Measuring UV Is Harder Than It Sounds
One reason the trends remain contested in fine detail is that measuring UV accurately at global scale is genuinely difficult. Satellites can estimate surface UV, but they rely on assumptions about what the atmosphere between the stratosphere and the ground is doing. A comparison of satellite-retrieved erythemal UV doses with ground-based spectroradiometer readings at northern and southern midlatitudes found that the hemispheric differences inferred from ground instruments were much larger than what the satellites showed. The conclusion was that tropospheric effects like low-altitude ozone and aerosol absorption were not adequately captured in the satellite retrieval algorithms.16Journal of Geophysical Research: Atmospheres. Satellite retrievals of erythemal UV dose compared with ground‐based measurements at northern and southern midlatitudes
Snow is another complication. UV albedo over Arctic snow (the fraction of UV reflected back up, some of which scatters to increase total exposure) ranges from 0.5 to 0.8 depending on whether the snow is fresh or melting, and it changes throughout the day.17Atmospheric Chemistry and Physics. Diurnal variations in the UV albedo of arctic snow As snow and ice cover shrinks with warming, this reflective surface disappears, which could reduce total UV exposure in polar regions even as ozone-related changes push it the other way. The interplay of these factors makes simple trend lines misleading unless the underlying assumptions are spelled out.
What the Models Project for the Rest of This Century
Future UV levels depend on which path the world takes on emissions. Climate models participating in the latest round of international comparisons have been used to project UV changes under several scenarios, from aggressive emissions cuts to high-emissions pathways.18PubMed. 21st century surface UV radiation changes deduced from CMIP6 models: part I-evolution of major influencing factors The projections show pronounced changes for the summer hemispheres in the far future (2081–2100), with the direction depending on latitude, season, and the balance between ozone recovery, aerosol changes, and cloud shifts.19PubMed. Projected changes in ultraviolet index and UV doses over the twenty-first century: impacts of ozone and aerosols from CMIP6
Under the most optimistic scenario (low greenhouse gas and aerosol emissions), the UV Index is projected to increase by up to 20% relative to the 1950s in Europe and North America, while decreasing by as much as 10% over tropical and polar regions.20PubMed. Twenty-first century surface UV radiation changes deduced from CMIP6 models. Part II: effects on UV index and plant growth weighted irradiance That result is counterintuitive at first glance: cleaner air in the developed world means fewer aerosols blocking UV, while the ozone layer overhead remains slightly thinner than in the 1950s even after recovery. In the tropics, ozone may actually overshoot its historical levels thanks to the stratospheric cooling effect from greenhouse gases, leading to a UV decrease.
The key takeaway from the modeling work is that UV is not going to settle back neatly to mid-20th-century norms. Even in the best-case climate scenario, some parts of the world will see UV levels higher than any generation alive today grew up with, while other parts will see less.
What Changing UV Means for Living Things
Marine phytoplankton, the microscopic organisms that produce roughly as much biomass as all terrestrial ecosystems combined, live in the sunlit upper layers of the ocean where UV-B penetrates. Research has shown that even ambient levels of UV-B radiation put many phytoplankton species under stress, affecting their photosynthesis, growth, and ability to incorporate nitrogen.21PubMed. Effects of solar UV-B radiation on aquatic ecosystems Because phytoplankton sit at the base of marine food chains and act as a major sink for atmospheric carbon dioxide, even modest sustained changes in UV-B could ripple through ocean ecosystems and global carbon cycling. On land, the interaction of climate change, ozone depletion, and altered UV-B affects crop growth, development, and yield.22PubMed Central. Ultraviolet-B radiation in relation to agriculture in the context of climate change: a review
Infrastructure takes a hit too. UV radiation degrades wood, plastics, and other organic construction materials, and any increase in surface UV combined with higher ambient temperatures from climate change will shorten the service lifetimes of these materials.23PubMed Central. Effects of UV radiation on natural and synthetic materials This is not a speculative concern. Local UV increases are still likely to occur, especially in the tropics and potentially elsewhere due to climate change effects, and such increases taken together with rising temperatures can significantly shorten service lifetimes of building materials.24PubMed. Interactive effects of solar UV radiation and climate change on material damage Architects and material scientists already factor in UV stabilizers, but the required level of stabilization may need to increase if UV exposure does not return to historical norms.
The Melanoma Puzzle
You might assume that if UV is increasing, skin cancer rates would track the increase almost perfectly. The real relationship is surprisingly tangled. A 2022 analysis of all U.S. counties examined the correlation between UV daily dose (a variable developed specifically for melanoma analysis) and melanoma incidence. The correlation was essentially zero. For comparison, smoking prevalence and lung cancer incidence in the same counties were correlated at 0.81. Melanoma incidence was instead correlated with median household income, and counties with the most dermatologists and primary care physicians had the highest incidence despite receiving lower UV doses than more rural, underserved counties.25JAMA Internal Medicine. Association of UV Radiation Exposure, Diagnostic Scrutiny, and Melanoma Incidence in US Counties
This does not mean UV exposure is harmless. There is decades of evidence linking UV to DNA damage, sunburn, and non-melanoma skin cancers. But it does mean that rising melanoma rates are not a straightforward barometer of rising UV intensity. Diagnostic scrutiny, screening access, and the definition of what gets counted as melanoma all appear to play outsized roles in the incidence statistics that headlines typically attribute to UV. If you are trying to gauge whether UV is getting stronger by looking at skin cancer trends, you are looking at a signal contaminated by at least as much noise from the healthcare system itself.