"Some say our planet is too crowded. I say we are 7 billion strong. But we will only be able to use that strength for the benefit of all if our societies are built on mutual respect and understanding," Moon said.
The world's population will reach the landmark seven billion mark on Monday.
Moon said the world must come together "on this special day... in the name of the global common good." He said while the world has made remarkable progress as it has aged, with more of its children surviving and more people living under democratic rule of law, the progress cannot be taken for granted.
The world is "under threat from climate change, economic crisis, joblessness, inequality and intolerance. Around the world, too many people live in fear. Too many people believe their governments and the global economy can no longer deliver for them," he said.
The answer to the current turbulent times is "unity of purpose." "Global problems demand global solutions. They compel all nations to unite in action on an agenda for the world's people."
The UN chief said the challenge for nations is to build a more just, tolerant and inclusive world. "We all have something to give and something to gain by appreciating each other's diversity and working together in common cause."
Meanwhile, UN Population Fund's Executive Director Babatunde Osotimehin said actions taken now will decide whether the future of the seventh billion baby will be healthy, sustainable and prosperous or marked by inequalities, environmental decline and economic setbacks.
"The world must seize the opportunity to invest in the health and education of its youth to reap the full benefits of future economic development or else face a continuation of the sorry state of disparities in which hundreds of millions of people in developing nations lack the most basic ingredients for a decent life," Osotimehin said.
He said planning and the right investments in people will empower them to make choices that are not only good for themselves, but also for a world of seven billion.
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