More than 2,000 representatives of 902 non-governmental organizations convened Wednesday at the United Nations to discuss climate change and an action agenda for how to proceed after 2015, the target date set in 2000, when UN member states adopted the Millennium Development Goals.

The conference – the largest such gathering since it began annual meetings 65 years ago — marked a “once-in-a-generation opportunity for transformational change,” said Jeffery Huffines, the conference co-chair, to a capacity crowd as well as to thousands more people who were watching the event on video screens in two overflow rooms at UN Headquarters and on the Internet. “Let us be ambitious and prepare to launch a global partnership for sustainable development in 2015.”

The conference theme is the role of civil society in the post-2015 development agenda with a focus on poverty eradication, sustainability, human rights and climate justice.

It comes less than a month before the Climate Summit, to be held 23 September, in New York, where more than 100 heads of state are expected to be in attendance. The issue of climate change is “more pressing than ever,” said UN Chef-de-Cabinet to the Executive Office Susana Malcorra. “We have a duty to be bold. That is what people want; that is what the world needs.”

The United States’ permanent representative to the United Nations, Samantha Power, noted that much progress has been made toward achieving the MDG goals. Since they were set, more than 600 million people have moved out of extreme poverty, girls and boys are now attending primary school in roughly equal numbers and nearly 14 million people have received lifesaving antiretroviral treatment for HIV/AIDS.

But those advances are threatened by an issue that was not even among the goals set in 2000. “Today, thankfully, we understand that if we don’t aggressively rein in climate change, its negative consequences could wipe out all of the progress we stand to make on other fronts,” she said.

Climate change has taught the world that the next set of development goals must consider the needs of people across the globe, not just in individual regions, she said. “Our new goals must be relevant for all countries, just as they must be defined by all countries,” she added. “This time around, our agenda must be a truly universal one.”