New York (CNN)Hindou Oumarou Ibrahim, a fiery 32-year-old from Chad, took the podium here at the United Nations on Friday morning in front of nearly 200 world leaders.
They'd gathered in record numbers on Earth Day to sign the Paris Agreement, humanity's best shot to date at fixing climate change and preserving a habitable planet for future generations.
But when she looked out at the crowd, her mind went blank.
Ibrahim didn't see the diplomats, she told me later.
She only saw her mother -- and her nomadic community in the Sahara.
So she felt compelled to tell their story.
In three languages, she spoke about how her mother used to walk 10 kilometers (6 miles) to get water from Lake Chad in North Africa. "Today young mothers are becoming climate refugees" because of drought, she told the assembly. "They cannot walk to Lake Chad because it is vanishing. Our pasture, our livestock, our food, our land -- is vanishing."
This was truly an historic Earth Day. Leaders from at least 175 countries came to New York to sign an international treaty that aims to limit global warming to well below 2 degrees Celsius. That's regarded as the danger zone for climate change -- when droughts get even worse and low-lying islands disappear.
They walked one by one up to a desk, sat down and signed their names, indicating their intent to help the world get off of fossil fuels by the end of the century and, hopefully, prevent catastrophic warming.
Signing the accord puts it one step closer to becoming international law. Nations still must ratify it on the national level. Several island states, which could disappear if the world keeps warming and seas keep rising at an alarming rate, already had ratified the agreement at home and submitted those ratifications to the United Nations at the ceremony Friday. In all, 15 countries ratified the treaty Friday, according to the United Nations.
Major powers, including the United States and China, promised to ratify the treaty this year.
Once 55 countries representing 55% of global greenhouse gas emissions have ratified the Paris Agreement, then it becomes law, and it's harder for countries to back out of it.
That appears to be a likely reality.
So there was plenty of hope in the room as world leaders gave speeches and patted themselves on the back for turning a major corner in the war against pollution and climate change.
They're right to do so.
But the speeches of two women -- Ibrahim and a 16-year-old from Tanzania -- underscored the importance of making sure this agreement becomes more than just a document with signatures.
It has to be translated rapidly into action. We have to stop using fossil fuels that warm the planet, causing ice to melt, seas to rise, droughts to intensify and floods and storms to worsen. We have to stop chopping down rain forests, which has a similar effect.
And we must, above all, do this quickly.
"We are in a race against time," said U.N. Secretary-General Ban Ki-moon. "The window (to hold temperatures at safe levels) is rapidly closing."
Ibrahim, the woman from Chad, described how hot it's already become.
"When I left last week it was 48 degrees Celsius (118 Fahrenheit)," she told me later. "It's crazy. Imagine. When they say it's 35 or 40 degrees (95 to 104 Fahrenheit) people are saying, 'Oh my god, it's so hot.' But for us 'too hot' is not just feeling it in your body and needing sunglasses to go out, or an umbrella to go out. For us, it's, 'Oh my God, it's too hot this year, what will be our survival? How will the rainy season be? Are we going to get calves? Are we going to get water?'
"That's the worry of the sun."
Drought and heat are "killing hundreds," she told world leaders, "in silence."
Getrude Clement, the bright-eyed 16-year-old from Tanzania who opened the ceremonies Friday, told me there already have been devastating floods in her community.
She wore a baby blue U.N. T-shirt and sneakers as she stood in front of a room of suits and declared that climate change is a moral crisis for everyone -- but especially for future generations.
"Climate change poses big problems for the entire plant," she told the room. "But children, especially the poorest and most vulnerable, will feel most of its effects, now and in the future.
"Climate change threatens our life, our Earth as well as our education. You might think we are too young to know about the risks and realities of climate change but we see it our daily lives. As young people the future is ours, but this is not the future we want for ourselves."
Clement, who helps produce a UNICEF radio program for young people in Tanzania, told me she's inspired by the Paris Agreement but it must become more than just a promise for change.
Together, these two women underscored the moral urgency with which we have to act on this crisis. The Paris Agreement sets a framework for real change to take place. But businesses, governments and everyday people have to agree to take action and make a real change.
Signing the document is an important, laudable start.
It's a turning point in the history of the world.
A decisive victory for future generations.
But let us remember Ibrahim and Clement.
At the end of our conversation, Ibrahim told me that she gets overwhelmed with emotion when she thinks of all the people back home in Chad who are counting on her to bring help.
People tell her they're putting all their hopes on her.
She teared up as she explained this to me.
Ibrahim feels the weight of this responsibility.
So should we.