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The planet is warming, and here’s one way to put the brakes on, if we dare: Block the sun. Or so says a cover story in Harvard Magazine, which describes how David Keith, an applied physicist at Harvard, is developing a technique for what’s known as solar engineering.

It’s not familiar to think of the sun as a problem, but in a sense it is: As we saturate the atmosphere with heat-trapping greenhouse gases, the real source of all that heat is the sun itself. If only we could dim the effects of our cherished star, we’d be free to emit to our hearts’ delight—or at least buy ourselves some time.

Blocking the sun sounds as impossible as emptying the oceans or flying across the galaxy, but as journalist Erin O’Donnell explains, Keith and other solar engineers think it might not be so hard. One idea is horizon-spanning space shields; another uses airplanes to shower the stratosphere with particles to reflect some sunlight back into space. Keith hopes to run small-scale field trials of that one.


The idea is littered with red flags. Keith himself worries it could be taken as a permission slip to keep on with bad habits. And at root the idea of blocking the sun is terrifying. Haven’t we all thrown in our lot with photosynthesis? Surely there has to be a better way to deal with global warming than to mess around with the single thing that almost all life on Earth depends on.

That is a global-scale decision, and one that our descendants may see differently than we do. One thing comes through plainly, though: To grasp the magnitude of the climate problem, it helps to consider just how alarming the solutions are.

The hidden patterns of Boston

In the middle of a busy day in Boston, the city seems to swirl with chaotic activity. If you sit in one place long enough, you’ll start to see patterns emerge—of color, shape, and rhythm—as absorbed pedestrians trace one another’s paths.

Photographer Pelle Cass has created an innovative series of images called “Selected People,” which reveals these hidden patterns in Boston life. He takes repeated photographs of the same public place, then artfully compresses elements into a single photo that creates the disorienting feeling of time and people’s lives stacked upon each other. If a place had a memory, it might look like this.



Cass, 58, typically shoots his photographs on his lunch break from his job as a graphic designer. He positions his tripod in a public space, like the Boston Public Garden or the shopping area at the Prudential Center, and takes 200 to 300 pictures in the span of about an hour. Sometimes he knows what he’s looking for, but just as often he’ll only begin to recognize the quirks and patterns in the images later, when he goes through them in Photoshop.

One image, constructed from a series of photographs taken at Quincy Market in the spring of 2012, transforms a jumbled crowd of pedestrians into concentric arcs. In another, taken on a pedestrian ramp along the Esplanade (above), Cass uses the same technique to make it look as though people had randomly ended up walking according to where their shirt colors fall in the visual spectrum. Not all of Cass’s photos are as pleasing, though. In one image, based on photographs of squirrels and pigeons around a tree in the Boston Public Garden, he turned a few wildlife-spotting moments into a tableau of infestation.

In an interview, Cass explains that he got the idea for “Selected People” while looking out his apartment window.

“I was just looking out my window and wondering what has happened on that little patch of sidewalk,” he says. “I realized that over the years it was probably almost totally filled with people.”


Cass’s work is delightful on the surface—fun, colorful, and satisfyingly ordered. But if you look long enough, it’s disturbing, too, as a reminder that each time we walk through a place, we’re wading through the ghosts of everyone who’s ever walked that way before.

You can see more at pellecass.com.

Kevin Hartnett can be reached at kshartnett18@gmail.com.