This letter is a bit more direct and longer than most of those which I write, but I hope you will be okay with that, because the times seem to call for being plain.

A few weeks ago I got a text message from an old and dear friend —let’s call her Hannah.

I have enough shared life with Hannah that, whenever we talk, the conversation always feels current and effortless, despite gaps of months or even years.

Hannah has been talking with her son — we’ll call him Neil — who is a teenager and doing well in school, but wildly worried about the state of the world, including the imminent trajectory of global warming. Hannah and I don’t text each other other very often, but on this occasion she’s reached out with something visceral:

Neil has challenged me to point him to something hopeful, if I can find it. He says so far no one is showing any will to uphold the Paris Agreement. I am checking in to see how you still manage to have real hope.*

Then, just a few days later, the United Nations Environment Programme Limiting Overshoot report landed, containing the principal finding that it is likely the global temperature will soon exceed 1.5°C.

After that news, and the real time devastation in Nepal, and in the context of the broader state of the world, I found myself having multiple conversations with friends and colleagues about the structure of hope. I want to openly share that after a few of these exchanges, I metaphorically closed the blinds, and wondered how to feel, and what to do, because there is no avoiding the dreadfulness of the news, and what it means for the suffering of people and life on Earth.

But if you are fortunate enough to have time, space and security to do so, then after the darkness, you open the shutters and once again there is light. This is the structure of my innermost resolve.

* * *

Our lives — those of us living on our magnificent earth now — have the greatest possible purpose.

There is virtually no problem that we endlessly clever and creative, human beings cannot solve, when we work together.

And we are not just intelligent and ingenious; we are inherently social, nurturing and brave; capable of the deepest enduring love.

Each of the roughly 12,000 generations of humanity so far has made life possible for those who have followed, through acts of devotion.

Babies have been held and fed. Water and food have been found and shared. Shelter has been built. For 12,000 generations we have held the hands of our children.

Every single one of us was once carried in the arms of another, unable to walk ourselves. It is our thoughtfulness, kindness and care that have seen us through as a species. Sometimes this has been in the most exigent of circumstances, when enough of our ancestors did not give in, faced incredibly difficult things, to somehow make it through.

And so it comes to this. To what we now must do. We must do as 12,000 generations of people did for us.

The struggle to keep global warming to under 1.5 degrees may be over. The battle of return—to get our planet back to safe temperatures at emergency speed and scale — is just beginning. Upon this struggle depends the future of all we care about, and that of all life on Earth. The prospects of the next 12,000 generations are conditioned by our efforts now.

Our work now is to keep the overshoot as low as we can, make it as brief as possible, and do everything within our power to alleviate other pressures on nature. It is to take care of humanity — of one another — in the face of mounting climate and ecological damage. And by these efforts, create the conditions for future flourishing. Every fraction of every degree matters.

What must now be done is hard, much tougher than should have been necessary, because of the vested interests in coal, oil and gas and deforestation, and the failures of decision makers. And while renewable energy has surged, making the case for change much simpler, on the other side of the ledger there’s the reactionary and gangsterist turn of politics and the multiplier effects of wars and mass violence, with the existential destabilisation of big tech looming over all.

There is no sugarcoating the scale of difficulty. But what is necessary remains within our collective power. We must never, for one second, say that returning our planet to flourishing is impossible — many of the obvious solutions already exist; but even where transformation relies on reforms, technologies or capabilities that might sound fanciful, or historical changes that are unprecedented, this can be no barrier to our conviction. After all, much of what we take for granted today as ordinary features of social life, would have been considered impossible by every single generation before us.

The world has not been destroyed by nuclear war; we solved the growing hole in the ozone layer; Antarctica was kept sacrosanct from exploitation. Humanity has collectively triumphed before, and can do so again.

We can find the necessary social and political will to do what is needed because these are endlessly renewable resources. The necessary financial capital exists. Apart from the fossil fuel industry, the greatest barrier we face is to mistakenly concede that what lies before us is insurmountable. It is not.

We must avoid the siren song of fatalism. Because. It. Is. Never. Too. Late.

None of which is to be insensitive to the horrors already unleashed — the deadly and grotesque harm to people, places and species that cannot be undone; or to be blind to the impacts that are coming. But where we have the power to act, we also have the responsibility — and the extraordinary privilege — to do what must be done.

Although she is wounded, our planet is still alive and beautiful beyond all of our comprehension. Hundreds of billions of creatures live and thrive still upon this earth. Nothing has happened until it has happened, and life fights for life. Every beetle, every tree, all the fish in the ocean, the smallest of the geothermal shrimps, the greatest of the whales and the mightiest of the birds — all demand life every second of their existence, so that their species too may have future generations.

No individual has to know how to solve this alone. Indeed, finding some detachment and humility is essential to concentrate on the role that each of us can play.

Hope is not merely a mindset or a story we tell ourselves. Collective power is not abstract; it is what we do, together, applying ourselves to the practical mechanics of change and contestation within society, by being part of the organisations and networks of people that are dedicated to effective strategies. It is why I am so committed to Greenpeace.

Working from without and within, there are opportunities to make rapid change within institutions, governments, businesses and communities to create the social, economic and political momentum for emissions reduction at speed and scale, reminding ourselves always of what remains possible, even if it hasn’t happened yet.

We can return the planet to safer temperatures. We can put technologies back in the service of people and life. We can return to the assumptions that seemed so obvious just one generation ago — that it is both possible, and our obligation, to build a better future for all people, and for life on Earth.

I did write back to Hannah and Neil, to say honestly to a treasured friend and her son, that yes, as a matter of faith, conviction, evidence and strategy, absolutely there is real hope. And this is a pledge not just to Neil and his generation, but to the next 12,000.

Together, we have the power. Together, we cross this bridge through the dark. To secure an Earth capable of nurturing life in all of its magnificent diversity.

We did not choose to carry this historic responsibility, but here we are. And it is so lucky that we are here.

I wouldn’t choose any other time to be here, alive on Earth, with you.

Alive on Earth, with you