Since 1972, the United Nations' World Environment Day has been marked in communities around the world but there was little notice paid to the event in North America.

That's probably because the global event was largely overshadowed by the much better known Earth Day - a grass-roots effort started in 1970 in the United States to raise awareness of environmental problems.

So in recent years, the U.N. has tried to integrate the two environmental celebrations by organizing a six-week series of events that launches in April before Earth Day and culminates on World Environment Day, which this year will be held June 5.

"[World Environment Day] has a huge following around the world but we have to admit that in North America, it's been challenging," said Elisabeth Guilbaud-Cox, deputy director of the U.N. Environment Programme's regional office in Washington, D.C.

Ms. Guilbaud-Cox is in Pittsburgh this week to help kickoff the events as the city plays North American host for World Environment Day 2010.

"Earth Day is really well known, but we don't want to challenge it," she said. "So we came up with the 'bridging the gap' concept." More than 100 events are scheduled in and around Pittsburgh during the World Environment Day time frame, ranging from scientific symposiums to interactive arts displays at the Three Rivers Arts Festival.

Pittsburgh follows Omaha, Neb., and Chicago as North American host cities. "We were trying to do outreach to the heartland of the United States and share with them the accomplishments of the U.N. Environment Programme and the work that we do," said Ms. Guilbaud-Cox.

The U.N. Environment Programme was created in 1972, the same year as World Environment Day, to coordinate scientific information and act as the U.N.'s "leading authority on the environment" and to help countries "set their environmental agenda," she said.

Among its accomplishments, she said, has been establishing the Montreal Protocol, which banned the manufacture of harmful compounds known as chlorofluorocarbons used in refrigeration units; and working to save some endangered species including elephants.

Bayer Corp., the German-based chemicals and drug company with U.S. headquarters in Robinson, was instrumental in making connections for Pittsburgh to host this year's World Environment Day, Ms. Guilbaud-Cox said.

While all the activities scheduled locally should expose the community to environmental issues, she believes the most significant event is the Water Matters conference, scheduled for June 3 at the David L. Lawrence Convention Center.

Water as a resource is the theme of the Pittsburgh events and the June 3 conference, expected to attract participants from outside the region, will feature business owners, community leaders and others providing expertise on how best to use and conserve water.

Another important event, she said, is a May 27 symposium at the Carnegie Museum of Natural History that is being organized by the Rachel Carson Homestead and will feature E.O. Wilson, a scientist and professor emeritus at Harvard University who provided Ms. Carson, a Springdale native, with research for her book, "Silent Spring."

A number of events converged in the city this week to mark the launch of World Environment Day activities.

As part of the kickoff, Global Pittsburgh is hosting representatives from 11 countries who are being encouraged to consider the city for potential business partnerships and economic development opportunities.

Among the delegation were officials from Vietnam, Canada, Ireland, Belgium, Czech Republic, Germany, the Netherlands, Oman, South Africa, Switzerland and the United Kingdom.

The group dined Wednesday night at the International Bridge Awards at Heinz Field and had lunch earlier in the day at Phipps Conservatory and Botanical Gardens.

Tours and symposiums on the group's agenda focused on local initiatives in energy, life sciences and education, and were designed to showcase why the city was selected for last year's G-20 Summit and as a host city for World Environment Day.

On Wednesday the delegates visited the energy center at the University of Pittsburgh in Oakland, and today the group was scheduled to attend panel discussions featuring experts in carbon capture, Marcellus Shale, nuclear, wind and solar energy sources before touring UPMC Children's Hospital in Lawrenceville.

Also Wednesday, the city hosted the Women's Health and the Environment Conference, a free event at the convention center where a capacity audience heard Teresa Heinz and other speakers discuss links between the environment and health.

And tonight, winners will be announced at the CAUSE (Creating Awareness and Understanding of Our Surrounding Environment) Challenge High School Film Festival at the Carnegie Science Center. Students from throughout the region were invited to produce and submit films of five minutes maximum length featuring this year's theme, "Mutual Impact: The Environment and You."

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