Retailers who want to grow sales in coming years need to “think global,” “think green” and “think mobile,” according to experts speaking Sunday at the National Retail Federation convention in Manhattan.

Global expansion, sustainable environmentally friendly business practices, and using smart phones and iPads to reach consumers were the hot topics as retail executives gathered for the world’s largest retail convention.

The annual convention is expected to draw more than 18,500 attendees this year, with advance registration running well ahead of last year. It also is the 100th anniversary of the first meeting of 37 retailers who formed the original retail industry group, the National Retail Dry Goods Association.

Attendees on the opening day of the conference were in a far happier mood than last year, reflecting recent news that consumers have begun to spend a bit more freely. The convention opened three days after news that U.S. retailers posted the best holiday results since 2006.

But speakers warned that retailers in the future will have to work harder than ever to grow sales, especially in developed countries such as the United States or England,

“Growth in developed markets has peaked,” said Richard Hyman, strategic advisor for accounting firm Deloitte LLP. In North America and Europe, there are already “too many retail mouths to feed – too much floor space, too many stores,” he said. “It is an industry that is self-cannibalizing increasingly.”

Hyman said global retail sales are forecast to grow by $6.1 trillion over the next five years, but that 66 percent of that growth will come in developing markets such as China and India, with only 21 percent occurring in mature economies.

Deloitte on Sunday released its annual “Global Powers of Retailing” report, which ranked the top 250 retailers based on worldwide sales in 2009, the most recent year for which final results are available. Toys “R” Us in Wayne ranked 63 this year, down one spot from 62 last year. Bed, Bath & Beyond in Union moved up 10 spots on the list, to 114. Bed, Bath also was ranked as one of the top 30 retailers in the world based on what Deloitte calls the “Q ratio” – the value the stock market gives to intangible assets like innovation and customer loyalty.

While the convention is hosted by the Washington, D.C.-based National Retail Federation, the gathering is very much an international affair, with international executives attending from more than 70 countries, and most speeches translated into several languages.

Ten of the 22 retail workshops presented Sunday dealt with sustainability, or ways to be a more environmentally friendly retailer. Author and retail researcher Paco Underhill, CEO of Envirosell, cited the example of a Dutch shopping “all” – a combination shopping center and village where the retail stores are located underground, topped with residences and green spaces. In an “all,” as opposed to a mall, he said, consumers can live, sleep, shop and eat all in one place.

Terry Lundgren, president and CEO of Macy’s Inc. and chairman of the NRF, welcomed the attendees to the conference and said localization of stores, so they connect with customers, also will be important going forward.

“Being locally and individually relevant will be the new standard for stores,” Lundgren said.