UNITED NATIONS, Sept. 10 (Xinhua) -- UN Secretary-General Antonio Guterres said on Monday that with climate change a direct threat to mankind youth should fight for their future and global leadership should "step up" to lead the campaign.

"Climate change is the defining issue of our time, and we are at a defining moment," he said. "We face a direct existential threat. Climate change is moving faster than we are."

"If we do not change course by 2020, we risk missing the point where we can avoid runaway climate change, with disastrous consequences for people and all the natural systems that sustain us," Guterres said in a major speech here at UN Headquarters, underlining the threat to future generations.

"That is why, today, I am appealing for leadership -- from politicians and leaders, from business and scientists, and from the public everywhere," he said. "We must break the paralysis. We have the moral and financial reasons to act. We have the tools to make our actions effective."

In roughly the next 10 years the world will invest some 90 trillion U.S. dollars in infrastructure.

"We must ensure it is sustainable or we will lock in a high-polluting dangerous future, and for that to happen, the leaders of the world need to step up," he said.

Guterres called on civil society and young people in particular to campaign for climate action. "Let us use the next year for transformational decisions in boardrooms, executive suites and parliaments across the world. Let us raise our sights, build coalitions and make our leaders listen."

He said it is time "for our leaders to show they care about the people whose fate they hold in their hands. We need them to show they care about the future -- and even the present."

"That is why I am so pleased to have such a strong representation of youth in the audience today," Guterres said. "It is imperative that civil society -- youth, women's groups, the private sector, communities of faith, scientists and grassroots movements around the world -- call their leaders to account."

The UN chief, in particular, called on the leadership of women and praising that leadership.

"When women are empowered to lead, they are the drivers of solutions. Nothing less than our future and the fate of humankind depends on how we rise to the climate challenge," he said. "It affects every aspect of the work of the United Nations. Keeping our planet's warming to well below 2 degrees is essential for global prosperity, people's well-being and the security of nations."

Guterres also said it was important for rich countries to help poor ones, which suffer the brunt of climate change, much of which has been blamed on rich, industrialized nations.

"There is no more time to waste," he said. "As the ferocity of this summer's wildfires and heat waves shows, the world is changing before our eyes. We are careering towards the edge of the abyss. It is not too late to shift course, but every day that passes means the world heats up a little more and the cost of our inaction mounts."

"Every day we fail to act is a day that we step a little closer towards a fate that none of us wants -- a fate that will resonate through generations in the damage done to humankind and life on earth," Guterres said.

The UN chief promised to make the same plea at the annual VIP-rich UN General Assembly General Debate beginning Sept. 25.

He already has scheduled a climate change summit for September 2019.