Supporters say there is no choice but to go big in a world of expanding population, growing inequality, dwindling resources and the existential threat from global warming.

A season of goal-setting begins this month as the United Nations launches a new 15-year plan to fight grinding world poverty, improve health and education and quell climate change.

The Sustainable Development Goals are set for adoption by the 193 U.N. member states shortly after Pope Francis brings his activist message to the world body on Friday – a message sure to include calls to pull back from the abyss of a heating world and to spread global wealth among the neediest.

More than 150 world leaders, including President Barack Obama and Chinese President Xi Jinping, are expected to speak at a three-day summit dedicated to adopting the goals. That meeting precedes the annual gathering of world leaders at the U.N. beginning Sept. 28.

The new goals land on the global agenda in advance of December’s world meeting in Paris aimed at a comprehensive agreement on curbing accelerating global warming.

The SDGs consist of 17 broad goals and 169 specific targets. They replace the United Nations’ expiring Millennium Development Goals, eight of them, adopted in 2000.

Despite significant progress, the only one of those original goals achieved before this year was halving the number of people living in extreme poverty. That was due primarily to economic growth in China.

Critics of the new goals say they are too broad, lack accountability and will lead to disenchantment among those in the world most in need of hope.

Supporters say there is no choice but to go big in a world of expanding population, growing inequality, dwindling resources and the existential threat from global warming.

“Let’s be realistic about this. This is about survival,” said Susan Brown of the World Wildlife Federation International. “We actually don’t have another choice. We are expanding into our natural resources at a rate which is not sustainable. And I don’t want to think about what the end-game looks like in 15 years if we don’t get this right.”

The goals are estimated to cost the world between $3.5 trillion and $5 trillion a year between 2016 and the end of 2030.

They were the work of a long process involving most countries as thousands of people came together in many gatherings to hash out the new agenda. It will be financed not only by the so-called “developed North” but also by the “needy South” from national development – reaping financial benefits from economic advances among people who are healthier, more equal and better educated.

The earlier Millennium Development Goals relied more on wealthy nations helping poorer ones, and were devised by people working for then-U.N. Secretary-General Kofi Annan.

That kind of top-down approach “wasn’t going to be the case,” with the new agenda, said Michael Elliot, CEO of One.org, an anti-poverty advocacy group. It was clear “the new development agenda had to be truly South as well as North, that it had to be universal, it had to be global, that it had to have from the start a component that reflected a whole set of concerns on the part of developing nations.”

Roger-Mark DeSouza, director of climate, security and population at the Wilson Center, applauds the goals and process that produced the new goals, but he worries about implementation. “That’s the crux of the matter, and I think that is still to be determined.”

“To make the goals realistic across these different country settings, there needs to be more opportunities for community engagement,” he said.

The 169 targets have not been fully outlined in terms of how success would be measured.

“The targets become critically important to watch in New York (when the goals are officially adopted),” said Ken Conca, an expert in water development and professor at American University’s school of international service. “The things that are most wildly aspirational tend not to be the targets.”

Secretary-General Ban Ki-Moon has praised the goals but warned that “further progress will require an unswerving political will, and collective, long-term effort. We need to tackle root causes and do more to integrate the economic, social and environmental dimensions of sustainable development.”