TWENTY-SIX years ago this month, a coalition of New Yorkers led by Jacqueline Kennedy Onassis won a historic victory for Central Park. At issue was a planned building on Columbus Circle by the developer Mortimer B. Zuckerman with 58- and 68-story towers that would cast long shadows on the park. After a lawsuit by opponents of the plan and a rally in Central Park at which over 800 New Yorkers with umbrellas formed a line to simulate the building’s shadow, Mr. Zuckerman relented and agreed to scale down his design, which eventually became known as the Time Warner Center.

“One would hope that the city would act as protector of sun and light and clean air and space and parkland,” Mrs. Onassis said at the time. “Those elements are essential to combat the stress of urban life.” Today, as the city becomes denser and green space ever more precious, New Yorkers’ access to sunlight and blue skies above Central Park is under assault in ways that make Mr. Zuckerman’s original plans look benign.

Fueled by lax zoning laws, cheap capital and the rise of a global elite with millions to spend on pieds-à-terre, seven towers — two of them nearly as tall as the Empire State Building — have recently been announced or are already under way near the south side of the park. This so-called Billionaires’ Row, with structures rising as high as 1,424 feet, will form a fence of steel and glass that will block significant swaths of the park’s southern exposure, especially in months when the sun stays low in the sky.

At New York’s latitude, explained Michael Kwartler, the president of the Environmental Simulation Center, a New York City nonprofit that creates shadow assessments, buildings cast substantial northerly shadows throughout the day in colder months. At noon on the winter solstice, for example, those shadows reach twice a building’s height and fall due north before stretching to 4.2 times its height in a northeasterly direction, 90 minutes before sunset.