Diane Ackerman on the natural world, the world of human endeavor and connections between the two.

In the sizzling summer heat I’ve been thinking about igloos. To chill out in, of course, but also because I admire their elemental simplicity. Inuits traditionally used bone knives to carve bricks from quarries of hardened snow. A short, low tunnel led to the front door, trapping heat in and keeping out fierce cold and critters. Mortar wasn’t needed, because the snow bricks were shaved to fit, and at night the dome ossified into a glistening ice fort. The human warmth inside melted the ice just enough to seal the seams.

The idea behind such homes was refuge from elements and predators, based on a watchful understanding of both. The igloo was really an extension of the self — shoulder blades of snow and backbone of ice, beneath which a family slept, swathed in thick animal fur, beside one or two small lamps burning blubber. All the building materials lay at hand, perpetually recycled, costing nothing but effort.

Picture most of our houses and apartment buildings today — full of sharp angles, lighted by bulbs and colors one doesn’t find in nature, built from plywood, linoleum, iron, cement and glass. Despite their style, efficiency and maybe good location, they don’t always offer us a sense of sanctuary, rest or well-being. Because we can’t escape our ancient hunger to live close to nature, we encircle the house with lawns and gardens, install picture windows, adopt pets and Boston ferns, and scent everything that touches our lives.

This tradition of doing and undoing doesn’t really make sense or promote healthy living or a sustainable planet, so there’s an impassioned trend worldwide toward building green cities with living walls and roofs and urban farms in skyscrapers. Referring to “the north 40” would mean crops 40 floors up. In such a cityscape, the line blurs between indoor and outdoor.

Vertical gardens and living roofs are sprouting up everywhere. Mexico City’s three eco-sculptures, carpeted in over 50,000 plants, tower above car-clogged avenues. A blooming tapestry of plants adorns the exterior walls of the Quai Branly Museum in Paris. Inside Lisbon’s Dolce Vita shopping center, a plush vertical meadow undulates. In Milan’s Café Trussardi, diners and flâneurs sit in a glass-box courtyard beneath a hint of heaven: a vibrant cloud of frizzy greens, cascading vines and flowers. The Plant, an old meatpacking building in Chicago, has morphed into an eco farm, home to tilapia fish breeders, mushroom gardeners and hydroponically grown vegetables. Xero Flor America, based in North Carolina, has already sold 1.2 million square feet of living roofs.

Jacob Magraw

Patrick Blanc, a botanist and a pioneer of the vertical garden (whose own house in the suburbs of Paris includes growing walls and an aquarium floor), has designed or inspired living walls for the New York Botanical Garden and a luxury apartment building in Sydney, among dozens of businesses, homes, schools and museums, whose walls whisper and bloom. The goal is homes and public spaces that are live organisms that will scrub the air of pollutants, increase oxygen, reduce noise, save energy and refresh the spirit. Roofs planted with low-maintenance sedums and succulents blossom, changing color with the seasons, providing a habitat for birds and, importantly, reflecting heat.

Big cities are hot spots, on average 13 to 16 degrees warmer than the surrounding countryside. On some summer days in New York City, the air hangs thickly visible, like the combined exhalations of eight million souls. Steam rising from vents underground makes you wonder if there isn’t one giant sweat gland lodged beneath the city.

A big worry to environmentalists is the record number of people fleeing suburbia for city life. Three and a half billion people now live in cities, and scientists predict that by 2050 cities will contain two-thirds of the world’s population and most of its pollution.

As people flock to urban centers where ground space is limited, cities with green walls and roofs and skyscraper farms offer improved health and well-being, renewable resources, reliable food supply, and relief to the environment.

A living building is really an entity with its own metabolism, which needs a brain of some sort to nourish it. That could be a human being, or better yet a robotic Jeeves (or maybe Leeves) who tends its herbal roof, meadow walls and human family with equal pride, and is a good listener. “Smart houses” already have plenty of bells and whistles run by savvy computer brains. Artificial intelligence is growing up fast, as are robots whose facial expressions can elicit empathy and make your mirror neurons quiver.

One can easily imagine the day, famously foretold in the movies “Blade Runner” and “2001: A Space Odyssey,” when computers feel pride, paranoia, love, melancholy, anger and the other stirrings of our carbon hearts. Then the already lively debate about whether machines are conscious will really heat up.

In J. G. Ballard’s science-fiction short story “The Thousand Dreams of Stellavista,” there are psycho-sensitive houses that can be driven to hysteria by their owners’ neuroses. Picture living walls sweating with anxiety, a vine-clad staircase keening when an occupant dies, roof seams fraying from a mild sense of neglect. Some days I swear I’m living in that house right now.