Skyscrapers are taking over the world.

A new study, co-authored by Yale urban environment professor Karen C. Seto, predicts a major global expansion of urban land over the next two decades. The study, which was published in the Aug. 18 issue of the journal PLosOne, projects that by 2030, cities will gain an amount of land roughly equal to that of Mongolia. This extensive and rapid growth will pose significant challenges to urban environments, the researchers said.

“Fifty years ago we had two mega-cities of ten million [people],” Seto said. “Right now, we have 19 megacities. In another 30 years, we’ll add about another 10 mega-cities.”

While the relocation of people from rural to urban areas has been well-documented, a systematic account of worldwide city land expansion had never been performed, according to the report. The research team, consisting of scientists from Yale, Stanford, Texas A&M University and Arizona State University, performed a meta-analysis on 326 English-language papers about urban land expansion to predict the global increase of “urban extent,” the fraction of land occupied by cities.

The environmental impact of urban land expansion is tremendous, Seto said.

“If cities are configured so that they take up increasingly more land it means that more people drive, as opposed to walk, from point A to point B,” she said. “If you think about the implications of that — across billions of urban people — it doesn’t matter how many emissions we reduce by switching to more energy-efficient cars.”

Urban sprawl, which environmentalists criticize for its tendency to increase pollution and energy inefficiency, is an urgent concern, Yale Student Environmental Coalition president Sam Bendinelli ’13 said.

“With a majority of people now living in cities,” he said, “intelligent land use policy is key to curbing the consumption of energy and natural resources in urban areas.”

Jeremy Madsen, the Executive Director of Greenbelt Alliance, a non-profit environmentalist group based in San Francisco, said cities will only become more important sites for intellectual and technological progress. The important question to ask, he said, is how people can build a symbiotic relationship with the non-urban environment.

Green spaces, such as parks and farms, can serve as watersheds, recreational areas, and food suppliers for city inhabitants, so they are a necessary piece of this relationship, Madsen said.

“We’ve lost a lot of those,” he said, “and we want to protect what we have left.”

To protect green spaces, policymakers can choose from several legislative tools, most of which concern zoning policies and building regulations, Madsen added. But these methods are not always possible, Seto said, because in many developing countries, the institutions required to pass and enforce such regulations are either lacking or nonexistent.

Nevertheless, many environmentalists and scientists remain optimistic about the 21st century, even as cities continue to proliferate and sprawl.

“Because of the challenges and the difficult times we’re living in, it’s a time of great opportunity [for scientists],” Madsen said. “And if we take advantage of that opportunity, maybe we can achieve some great things.”

The world’s most populated city is Shanghai, which contains 14.3 million residents and spans 6,340 square kilometers.