More than 15,000 participants from around the world converged in Copenhagen for two weeks in December during the United Nation's 15th Climate Change Conference (COP15). The conference was a golden opportunity to showcase an impressive array of investments and initiatives that have put Copenhagen in the forefront of green-meetings destinations. Here's a look at a few.

Copenhagen's King's Square twinkled greetings to COP15 attendees.

Convention Centers: The main venue for COP15 and the largest convention center in the Nordic countries, the Bella Center has invested millions of dollars in energy-saving measures, resulting in a 20 percent reduction in CO₂ emissions from 2007 to 2009. These efforts include installing a windmill in the parking lot, LED lights, new insulation, and upgraded heating systems. The center offers only filtered tap water, cutting 100,000 plastic bottles of waste a year.

The city's new Tivoli Congress Center, seating up to 4,000 people, will open later this year with a Green Key ecolabel, which sets standards for responsible energy and water consumption, waste reduction, and use of organic produce.

Transportation: Both the Bella and the Tivoli convention centers cut transportation costs and emissions. Tivoli is walking distance to the town center, while the Bella is a 20-minute train ride from downtown. (It's estimated that 95 percent of COP15 delegates used public transportation.) Indeed, Copenhagen's vaunted public transportation includes an extensive train and monorail network, as well as a growing number of buses, taxis, and sightseeing boats that use either electric batteries or biofuel. The city has one of the world's first city bike systems, providing free rental bikes, and about 35 percent of Copenhageners bike to work or school year-round.

Denmark's leading airline, SAS Scandinavian Airlines, has announced its goal to reduce greenhouse gas emissions by 20 percent by 2020, with a vision of zero emissions by 2050.

Hotels: Close to 50 percent of Copenhagen hotels have earned an ecolabel (such as the EU Flower, Nordic Swan, Green Key, and/or ISO 14001), according to the city's convention and visitors bureau. The Nordic chain Scandic, with nine hotels in Copenhagen, was recently awarded the IMEX Green Meetings Award for its sustainability efforts. All 10 properties of Arp-Hansen Hotel Group, builders of the new Tivoli center and its adjacent 400-room hotel, have earned a Green Key.

Opened just weeks before COP15, the 366-room Crowne Plaza Copenhagen Towers has set the bar high for sustainable hotels. The CO₂-neutral building has a groundwater based heating and cooling system and a solar-panel-covered façade. The hotel uses no fossil fuels.

The Danish-owned Brøcher hotel chain is the world's first CO₂-neutral hotel chain. Each year Brøcher purchases carbon credits corresponding to its calculated collective CO₂ emissions. Choice Hotels, the largest chain in Scandinavia, has cut its energy consumption by 20 percent since 2003.

Organic Food: According to Copenhagen's convention bureau, 51 percent of all food consumed in the city's public institutions (including conference facilities and museums) is organic, and the city is aiming to increase that to 90 percent by 2015. There has been an explosion of organic eateries in the city, including at the Hilton Copenhagen Airport Hotel, which received its Green Key certification in 2009.

Conference Management: Charged with organizing COP15, the Danish Foreign Ministry understood that security concerns would trump any environmental issues, but that didn't stop them from conceiving COP15 as an environmental case study. A consortium of government and tourism agencies was formed and a consultant was hired to document and measure the environmental impact of COP15. The resultant Copenhagen Sustainable Meetings Protocol, expected to be published this month, was designed as a tool to spur large international conferences to greater sustainability measures.

One example of the many ways COP15 organizers cut waste was to forgo conference bags and gifts for delegates, using the money instead to buy scholarships for 11 students from around the world to study climate change at Copenhagen schools.