NEW YORK ― The world can breathe easier with the reelection this month of United Nations Secretary-General Ban Ki-moon to a second term in office. In a fractious world, global unity is especially vital. During the past five years, Ban Ki-moon has embodied that unity, both in his unique personal diplomacy and in his role as head of this indispensable global organization.

Winning reelection to lead the U.N. is no straightforward matter. As head of an organization of 192 member states, the secretary-general inevitably feels the powerful crosscurrents of global divisions. On almost any issue, the secretary-general is likely to find himself between contending groups of countries. Yet Ban has inspired global confidence in his leadership to the point of securing an uncontested and unanimous second mandate.

The consensus in favor of Ban’s reelection is all the more striking because it includes the so-called P-5, the five permanent members of the U.N. Security Council ― the United States, the United Kingdom, China, France, and Russia. These five powerful countries owe their U.N. preeminence to the post-World War II settlement, when they were allies in victory. Under the U.N. Charter, all five must endorse the election of every secretary-general. Ban Ki-moon has maintained the strong backing of all five permanent members.

I have the honor to serve as the secretary-general’s special adviser on the Millennium Development Goals. In that capacity, I see the secretary-general in action in all parts of the world. It is a rewarding experience, one that gives me great hope for ultimate success in resolving global problems such as poverty, environmental threats, and violent conflict.

The world’s many problems make their way to the secretary-general’s office day and night. Whether the issues are war and peace; revolutions and coups; natural disasters; epidemics; disputed elections; or the grinding challenges of hunger, poverty, climate change, and mass migration, the crises inevitably demand the secretary-general’s attention. It is a workload that boggles the mind, and demands the round-the-clock commitment of the secretary-general and his team.

During a recent trip with Ban to Egypt and Tunisia, I watched in awe as he deftly backed the democratic changes underway in those two countries while simultaneously dealing with many other upheavals in the region. Ban generously and inspiringly offered his support to the brave youth leaders in both countries who are at the forefront of the political changes set in motion this year.

From his first days in office, Ban emphasized that many or most of the world’s greatest challenges come down to a simple yet stark reality: we are now a crowded, interconnected, global society, with seven billion people struggling to find a foothold on a highly vulnerable planet. The challenges of feeding the world, keeping it safe from epidemic diseases such as malaria and AIDS, and combining economic progress with local and global environmental safety are the defining challenges of our time. War and violence often have as underlying causes hunger, poverty, and environmental degradation, such as human-induced climate change.

We are, in short, in a new global era, which may be defined as the Age of Sustainable Development, in which our security, even our survival, will depend on the world forging a triple commitment: to end extreme poverty; to ensure human rights for all; and to protect the natural environment from human-induced crises of climate change, destruction of biodiversity, and depletion of fresh-water reserves and other vital resources. Ban has tirelessly emphasized the need to put sustainable development at the center of our thinking.

The challenges of poverty, resource depletion, climate change, and human rights will dominate Ban’s second term, and the work of those who will follow him as Secretary-General. In 2012, world governments will reunite in Rio de Janeiro, 20 years after the historic conference at which they signed the first comprehensive treaty to fight human-induced climate change. Far too little has been accomplished since, and, behind the scenes, Ban is working relentlessly to clear the bottlenecks and avert climate disaster.

At the start of the third millennium, Ban’s predecessor, Kofi Annan, brought the world’s leaders together to adopt the Millennium Development Goals, which established ambitious targets to be achieved in the fight against poverty, hunger, and disease by 2015. Ban has been a tireless champion of the MDGs, and has initiated several highly creative campaigns to enlarge worldwide engagement with them.

This past year, for example, Ban launched a bold new global initiative, “Every Mother, Every Child,” to improve health care for women and children. He has championed the fight against HIV/AIDS, tuberculosis, and malaria, bringing many global leaders and public figures to the cause. Under Ban’s leadership, remarkable progress is being made, though as he emphasizes, even faster progress is both possible and needed. In 2015, the secretary-general will help guide the world towards even bolder commitments in the fight to end extreme poverty and deprivation in the coming two decades.

There is a great personal satisfaction in Ban’s own story, one that gives hope for all. When Ban travels to Africa’s impoverished regions, he mingles with villagers and recounts his own upbringing amid the poverty and deprivation of Korea in the 1950s ― and how, by committing itself to hard work, education, modern science, and shared values, South Korea became one of the world’s richest and most successful countries.

Ban’s rise from poverty to global leadership parallels his country’s trajectory. It is a story of decency, commitment, and generosity that has won global confidence, and that can help to guide the world at a time of unprecedented risks and unique opportunities.

By Jeffrey D. Sachs

Jeffrey D. Sachs is a professor of economics and director of the Earth Institute at Columbia University. He is also special adviser to the U.N. secretary-general on the Millennium Development Goals. ― Ed.

(Project Syndicate)