The Sunniest Place on Earth Is a Frozen Desert Where Sunlight Can Rival Venus

If you wanted to find the most intense sunlight on Earth, you’d probably look somewhere unbearably hot. The Sahara, perhaps. Or Death Valley, where summer temperatures can get hot enough to fry an egg on the pavement.

You’d be looking in the wrong place.

High in Chile’s Atacama Desert, more than five kilometres above sea level, lies a barren, windswept plateau where the air is thin, the nights are bitterly cold, and the sky is almost impossibly clear. It’s not exactly anyone’s idea of a tropical paradise.

But this unlikely place gets absolutely hammered by the Sun.

In January 2017, a scientific instrument on the Chajnantor Plateau recorded a burst of sunlight so powerful that it approached the intensity of solar radiation near Venus, the second planet from the Sun. For a brief moment, a patch of Earth’s surface received an extraordinary 2,177 watts of solar energy per square metre.

That’s a staggering amount of sunlight. And what makes it even stranger is that clouds helped make it happen.

The sunniest place on Earth is surprisingly cold

The Atacama Desert is already a land of extremes. Wedged between the Pacific Ocean and the Andes, it is one of the driest places on the planet. Some parts have gone years without measurable rainfall. It’s so bizarre researchers sometimes use it as a proxy for Mars.

None of this is new. But there’s something else extraordinary about this landscape that isn’t talked about as much. The Altiplano, the vast high-altitude plateau stretching across Chile, Bolivia, Peru, and Argentina, receives an almost absurd amount of solar radiation.

Scientists had suspected this for years. Satellites consistently identified the region as Earth’s most intensely irradiated landscape. But there was a problem: satellites could only tell so much about what happened down on the ground.

To settle the question, researchers installed an atmospheric observatory called a pyranometer in 2016 near the edge of the Chajnantor Plateau, at an altitude of 5,148 metres (16,890 feet).

Measuring sunlight

A pyranometer is a small device that measures the amount of solar energy falling on a surface.

Unlike instruments that detect only visible sunlight, it also captures ultraviolet and near-infrared radiation, both of which contribute to the Sun’s total energy. For five years, the observatory quietly recorded what the Sun was doing.

The results were extraordinary.

The plateau received an average of 308 watts of solar power per square metre, counting both daylight and nighttime hours. That’s roughly twice the average reported for Central Europe and the eastern United States, and even higher than measurements from near the summit of Mount Everest.

In a study published in the Bulletin of the American Meteorological Society, the team confirmed that the Altiplano was indeed a record-breaking solar hotspot.

“The Altiplano of the Atacama Desert is the most irradiated place on Earth. Due to its proximity to the equator, the annual irradiation (i.e., the annual dose) is far higher (more than 20%) on the Chajnantor Plateau than in other high-altitude regions,” the researchers note in the study.

But buried in those five years of observations was something even more remarkable.

For a while, it was almost like Venus

In January 2017, the instrument registered an astonishing peak of 2,177 watts per square metre.

To appreciate how extraordinary that is, consider that the Sun normally delivers about 1,361 watts per square metre to a surface facing it just outside Earth’s atmosphere, at Earth’s average distance from the Sun.

And that’s before the atmosphere absorbs or scatters some of that energy.

Yet here was a patch of ground in Chile receiving far more. The amount of incoming sunlight briefly approached what you’d encounter in space near Venus’s orbit. Venus is millions of kilometers closer to the Sun than Earth and has a mean temperature of 464 °C (867 °F).

“It’s actually the radiation that you will be receiving in summer if you are standing up on Venus,” Raul Cordero, first author of the 2023 study and a climatologist at the University of Groningen, told The Washington Post.

This all begs the question: why? Why is this place getting so much sunlight?

Sometimes, the clouds bring more sunlight

We tend to think of clouds as enormous sunshades. They block sunlight and cool the ground; seems straightforward.

Alas, it’s not that straightforward.

If you’ve ever seen the Sun just as it emerges from behind a cloud, the light seems almost painfully bright. The glare becomes very intense, and you’re not imagining it.

Under the right conditions, clouds can actually increase the amount of sunlight reaching a particular spot on the ground. The phenomenon is called cloud enhancement.

Here’s how it works.

Imagine the Sun shining through a gap between clouds. Direct sunlight reaches the ground as usual. But sunlight also strikes the surrounding bright cloud edges, where some of it is scattered toward the same area.

The clouds aren’t creating extra energy, of course. But they redistribute sunlight that would otherwise travel in different directions. When conditions line up just right, the results can be dramatic. That’s what’s happening in Altiplano.

So the most sunlight didn’t come when there were no clouds. It was the clouds, those supposedly reliable blockers of sunlight, that helped push the radiation to extraordinary levels.

Why this frozen desert gets so much sunshine

This phenomenon only explains a part of why Altiplano is such an extraordinary solar hotspot. Several geographical and atmospheric quirks make the region almost perfectly positioned to receive powerful sunlight.

First, there’s the altitude.

At more than 5,000 metres above sea level, sunlight has less atmosphere to pass through before reaching the ground. That means fewer opportunities for incoming radiation to be absorbed or scattered.

Then, there’s the dryness.

Water vapour absorbs some of the Sun’s energy, particularly in infrared wavelengths. The Altiplano’s exceptionally dry air contains very little of it. Concentrations of aerosols and ozone are also relatively low.

And the sky is frequently clear. Together, these conditions allow an unusually large fraction of incoming solar radiation to reach the ground. There’s even a small astronomical bonus.

Earth’s orbit isn’t a perfect circle. Our planet reaches its closest point to the Sun, known as perihelion, in early January, which happens to be summer in the Southern Hemisphere.

That means southern summers receive up to about 7% more incoming solar radiation than northern summers because of the difference in Earth–Sun distance.

Together, all these conditions lead to high amounts of sunlight concentration in the Altiplano.

So then why isn’t it scorching hot?

Because sunlight and air temperature aren’t the same thing. Sunlight is only part of what determines how warm a place gets.

The Sun provides most of the energy that heats Earth’s surface, but the air above it is warmed largely from below, as the ground transfers heat through convection, infrared radiation, and direct contact.

How much of that warmth sticks around depends on the atmosphere.

Greenhouse gases, especially water vapour, absorb infrared radiation and slow the escape of heat into space. At Chajnantor, more than 5,000 metres above sea level, the air is exceptionally thin and dry. There’s less atmosphere to retain warmth, and the surface loses heat rapidly, particularly after sunset.

The result is a strange combination: sunlight powerful enough to rival conditions near Venus, but air temperatures that can hover around freezing.

A solar goldmine with an unexpected problem

So if this place is so sunny, why don’t we just slap a bunch of solar panels on it?

Northern Chile does indeed have enormous potential for solar energy production. The region’s exceptional annual sunlight makes it one of the most attractive places on Earth for harvesting energy from the Sun.

But the extraordinary bursts of sunlight are actually a problem in Altiplano.

Solar panels don’t particularly appreciate sudden, dramatic changes in incoming radiation. Their electrical output can change rapidly as clouds move across the sky, creating challenges for inverters and electrical networks.

There are also implications for human health.

“At this particular location, for people working there … they are aware that the radiation was high, but now we know how really high. If you are exposed to such a high radiation danger, you have to protect your skin.” Cordero said.

Even so, the discovery reveals something remarkable about an ordinary-seeming part of our planet.

There is a cold, lonely stretch of desert high in the Andes where the atmosphere is so transparent, and the clouds can behave so strangely, that the Sun occasionally delivers a burst of energy approaching what you’d expect much closer to our star.