The road to the Paris climate talks has been paved across decades.
And as leaders convene in the capital today, they'd do well to look to those campaigners - past and present - whose resolve, courage and vision has roused the world to reach this moment.
Trailblazers including the late biologist and environmentalist Rachel Carson, who so compellingly sounded the alarm bells on signs of climate change.
Echoing now down five decades, Carson's Silent Spring remains a piercing wakeup call as we finally arrive at this defining crossroad: 'We stand now where two roads diverge,' she said back in '62. 'The road we have long been travelling is deceptively easy, a smooth superhighway on which we progress with great speed, but at its end lies disaster. The other fork of the road - the one less travelled by - offers our last, our only chance to reach a destination that assures the preservation of the earth. The choice, after all, is ours to make.'
We don't have another half century to drag our feet. This year we reached the halfway mark to dangerous global warming.
But fifty years on from Carson's crossroads, we have hope still. I saw it at the People's Climate March yesterday - and it's a force to be reckoned with.
That hope must now be translated into action - and that action must be sustained.
I've attended many of these summits, and I agree the lead-in to Paris feels different. It won't offer a full stop, but it does present a brave new chapter - one that shouldn't be left to governments alone to write.
In Parliament, Paris and across our communities, Labour is standing up for jobs, justice and climate action. We're fighting for community energy initiatives, warmer homes and crucial flood defences - and fiercely opposing the Government's assault on renewables. I'm proud that the last Labour government passed the Climate Change Act - a visionary move and global first. And that, just last week, 50 Labour councils boldly pledged to run their cities entirely on green energy by 2050.
But a climate revolution must also be a people's movement - globally and locally - and they must to be able to hold governments to account on the Paris pledges.
In the same decade Carson gave us Silent Spring, Robert F Kennedy - whose brother John defended Carson's work against the inevitable backlash from polluting industries - told us the future 'does not belong to those who are fearful of new ideas and bold projects'.
Yesterday's climate marchers championed a bold, forward-looking narrative that can inspire our children for the next fifty years. They marched for clean energy and healthy air. They marched for forests filled with life and oceans teeming with fish. They marched for sustainable living as an opportunity, and for climate action as a matter of social justice.
This month the World Bank warned that, without urgent action, climate change could push 100 million more people into extreme poverty in the next 15 years. Since 2008 natural disasters have displaced one person every second, and it's a rising trend. In 2013, three times more people were displaced by natural disasters than by conflicts and, in 2014, 17.5 million were displaced by extreme weather events.
Our march yesterday to protect the planet was also our fight to alleviate poverty and water scarcity, promote stability, ensure food and energy security, address global health, education and gender equality, create jobs and stimulate sustainable economic growth. It's the fight to protect UK homes and businesses from flooding, and families in Ethiopia from famine.
We can't afford not to act. Whether you're a banker or a botanist - the economic benefits of a clean energy revolution are compelling.
But in the UK, scattergun Government cuts to subsidies, jobs and - with it - investor confidence is severely stunting growth. The UK is now falling 10% short on its legally-binding emissions targets.
We're setting bolder targets yet being locked further into a polluting fossil fuel future with a limited lifespan. Gas must be off the grid within 20 years if we're to meet our emissions pledges, but - days before the Paris summit - the Conservative government announced further subsidies for the sector.
I will be in Paris this week, fully supporting any government that attempts to secure a bold and binding agreement - I'll also continue to hold our UK government to account in Parliament if it falls short on its commitments.
At COP21, we need:
•Leaders to do more to help poorer countries transition from high fossil fuel dependency to a new low carbon economic model and mitigate climate change impacts. These are the countries feeling the sharpest edge of a crisis they didn't create
•Independent and legally binding safeguards to ensure Government promises are kept. That will require robust and transparent recording, monitoring and verification of emissions in each country
•But even if every country sticks to its Paris pledge - which would be an incredible step forward - the earth's temperature would still rise by at least 2.7C: beyond the dangerous threshold. At the very least, we need a clear and robust system to ensure current promises can be tightened or ratcheted up
From Rachel Carson and other visionaries we inherited the warnings of climate change. It has taken us too long to arrive at Paris. Now we must be the visionaries for future generations. They will judge us on the road we now choose.