Times Square is getting ready for a major celebration to welcome in a new decade this New Year's Eve. Twenty years ago, I attended the extravaganza as an eight year old:

Clearly, a lot has changed in New York City since 2000 — and more than just how I look.

New York University Professor Mitchell Moss, who's experienced more than 60 New York New Years, says the 9/11 terror attack was a major turning point.

"After September 11, people thought New York had no future,” said Professor Moss. “Who would live here, who would work here, who would study here, and just the opposite has come true."

Since then, tourism has surged to nearly 70 million visitors a year, and the number of people living and working here has hit records, too. But there is a downside to New York's new popularity.

Due to a lack of affordable living space, rents in some parts of the city are now at all-time highs.

Another turning point for New York came in 2012, when Superstorm Sandy blew through.

"Although it hurt, devastated parts of Staten Island and the Rockaways, it has become the impetus for New York to be aware of climate change," said Moss.

You can see the Sandy effect along the coast, from boardwalks rebuilt with concrete instead of wood to newly designed barriers protecting against storm surges.

The push for sustainability is reflected in newly designed skyscrapers that are more energy efficient, and new laws that trying to make plastic bags and straws a thing of the past.

Another major change: smartphones that have transformed how New Yorkers live, work and explore.

"I think it's just made a lot of commute easier, and just, like, tackling the city faster," said one New Yorker.

Apps like Seamless and Open Table are exposing us to new foods in distant neighborhoods; dating apps are introducing people who otherwise would not meet; rideshare apps like Uber and Lyft make getting around town effortless — as long as the traffic is OK.

According to Mitchell Moss, if the past 20 years are any indication, there are still far more questions about the future than we have answers for

"The great challenges of New York can't be predicted, but we will face them nonetheless," Moss said.