Scientists are warning that New York City is becoming increasingly vulnerable to a Katrina-like hurricane, and they are blaming global climate change.

“We are ill-prepared and action is urgently needed,” a senior research scientist at Columbia University, Klaus Jacob, said yesterday at a City Hall hearing convened by the City Council’s Infrastructure Task Force.

Experts testified that the worst-case scenario for New York is a hurricane making landfall off the New Jersey coast, as the worst winds would be directed toward the city, causing widespread flooding. Mr. Jacob estimated such a storm could cause hundreds of billions of dollars in building damage and that additional billions would be required to repair the city’s infrastructure.

A professor at Stony Brook University, Douglas Hill, testified in favor of investing in a series of barriers to reduce the impact of such a powerful storm. He noted that the Weather Channel in 2006 named New York the third most vulnerable city to hurricanes in the country, behind Miami and New Orleans, and that rising tides due to melting ice caps could make storms more frequent and flooding more severe in the future. He estimated that a barrier system would cost about $5 billion to implement, but said it would be worth the expense to minimize harm from an otherwise devastating storm.

Officials from the Department of Environmental Protection and the Office of Emergency Management told council members that the city was working to gather more information before embarking on a large-scale project of the type Mr. Hill described.

“There’s a whole menu of options,” the deputy director of the city’s Office of Long-Term Planning and Sustainability, Ariella Maron, said. “Nothing has been ruled out at this point.”