Gilchrist should know. Gensler is behind the newest addition to Shanghai's skyline: Shanghai Tower, a colossal 2,073-foot-tall skyscraper set to become the third-tallest building in the world (after Dubai's Burj Khalifa and Tokyo's Skytree) when it begins operations in mid-2015. It boasts 121 floors, nine dividing sections, and a twisting facade. As its designers call it, the tower will be a “vertical city”—it looks like a city street turned to point upward, with each of the nine sections serving as a “block.” With its massive height, the tower will eke in just ahead of the Abraj Al-Bait Towers (1,972 feet) of Saudi Arabia and Taipei 101 (1,671 feet) in Taiwan. It dwarfs the 1,776-foot tower at One World Trade Center, the tallest tower in the United States. (The Willis, née Sears, stands at a paltry 1,451 feet in Chicago.)

Shanghai Tower will also join the growing number of completed skyscrapers in Asia. The Council on Tall Buildings and Urban Habitat, in its 2014 Year in Review, showed how the completion of skyscrapers (classified as 200 meters—about 656 feet—or taller) underlined transitions in world economic power:

Locations of the World's 100 Tallest Skyscrapers

But even as architects continue to build skyscrapers, the goal of building taller ones has changed. Designing the skyscraper of the future isn't so much about scraping or even piercing the sky, but using it to make its space more efficient than ever.

“The ‘tall building’ embodies that futuristic Blade Runner city, but I'm not necessarily convinced you need tall buildings to evoke that,” Gilchrist says. “We're striving for high performance in our buildings.”

This “high performance” can mean many things: added comfort, better energy conservation, more control for building tenants, etc. Cities will always need more space, which they'll find by building upward, but they also need to meet the needs of people living in a changing world.

That's not an easy task, as it's become harder for engineers to make buildings even taller than before. Take the Sky City project in Changsha, China, for example. The tower was supposed to not only become taller than the Burj Khalifa, but was also supposed to be built in just three months. Delays in design, construction issues, and pushback in the region have left the project on hold.

For most other skyscrapers, though, the challenges begin with elevators, which is the “real limit to technology” designers have faced, as Gilchrist puts it. Steel cords can hold only so much weight before the load becomes too heavy to carry, especially when traveling dozens of floor upward, and elevator cars can move only so fast. The fastest elevator, which will be used in the CTF Financial Center skyscraper in Guangzhou, China, when it opens in 2016, will travel at about 20 meters (about 66 feet) per second. Those speeds can be unforgiving on the bodies—and ears—of their riders.