Sometimes you can see the end of the old world and the beginning of the new one as clearly as a seam. Transformations that were once barely perceptible, recognisable only after the fact, this summer have become akin to a crossing. You can see the line as you step over it.

It’s the first summer of this new decade. Welcome. It’s the summer of ash washed up on the beaches, like a long, deranged message unfurled from its bottle. It’s the summer of a billion animals killed by flames and starvation, it’s collapsed biospheres, charred forests, epic dust storms, hailstones and racing clouds carrying fire.

It’s the summer of the worst air quality in the world, of breathing masks and of keeping children indoors. It’s the summer of cancelled holidays, of anxious evacuations on jammed roads out of coastal hamlets. It’s fire raining on beaches, and skies that glow red at night and darken in the day. It’s the summer that Australia’s colours on Instagram went from saturated to sepia, starting in early December when people in Sydney shared photos of the weird red sun. The image at first seemed singular and disorienting until it was repeated so often (so many skies, in different cities, on so many feeds) it just came to be disorienting, and later very familiar.

It’s the summer of asking about people’s holiday plans and also their fire plans. It’s the summer of both generalised and specific anxiety – where despair and dread coalesced into a sort of collective bad vibe and common understanding that this is a terrible summer.

I found myself deep in plans with strangers to join some agrarian farming collective

It’s the summer when faith in the political class entered some new, nihilistic nadir, where the national hero was the volunteer firefighter who said on camera that the prime minister should “get fucked” and if we believed in such a thing as a centre we would say this was the summer the centre no longer held.

But it’s also the summer where we held and kept faith with each other: people saving their neighbour’s home at risk to their own safety; people driving hundreds of kilometres with food for fire-affected regions; people donating water to drought-stricken farms; every coffee shop and concert and celebrity hosting a fundraiser.

It’s the summer when what we thought of as the union between humans and the natural world seemed suddenly and irrevocably rent. The contract was nullified. The collapse appeared total at times. A billion animals died. Some species may never return.

It’s the summer when climate change stopped being something we talked and argued about, an abstract thing to be debated. Instead it was the ash we breathed into our bodies, the devastation we saw with our eyes and pain felt in our hearts. When you feel it there, you can no longer deny it.

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Those of us several degrees removed from the fire zone – who had stayed in the cities or on the unburnt side of Victoria – experienced fires as an anxiety-generating, feral echo. It was the smoke in the air and sudden drops in temperatures – 46 degrees one day, 20 the next, dust storms and large lumps of hail.

This summer, Sydney was a ghost town, populated by sad looking people in breathing masks. The lockout laws were repealed but it seemed like a bad time to restart the party. People stayed at home and ordered UberEats.

The world’s media reported our situation with alarm. For a nation that craves attention we should have been pleased to be first at something. But being on the frontline of a major climate catastrophe didn’t feel so good.

Expats felt a sudden need to return home, the way you rush to the airport and board a red eye to visit a relative on their deathbed.

Some immigrants who had come for the “lifestyle” were similarly rethinking their choices, and talking of making the journey in reverse.

The good life in Australia wasn’t looking so good any more.

For Australians, a collective grief emerged. We yearned for the past. All summer, we spoke of previous summers – long, dusky days and evenings at the beach, unbroken weeks of sunshine and clear water, skin browning, and the days and weeks merging like a hot, salty dream – as if they were scenes from another epoch, a lost idyll.

Part of the anxiety of this summer was that the idyll might be gone forever. In its place was strange, unpredictable weather and humans and animals that moved through this weather tentatively and with a measure of fear.

It’s the summer where for the first time I heard people, young people not usually prone to hyperbole or paranoia, speak plainly about the world ending.

My Sydney GP told me he had seen four people already that day with climate change-related anxiety and depression. He was offering them antidepressants.

At a lunch in Bondi, someone said we have 60 harvests left before the world will run out of food.

That everyone she told was alarmed and also accepting of this, and that also no one seemed to know exactly what a harvest was (is it annual, we asked – like yearly??) seemed to be both an allegory and an explanation for how we had got here.

After some weeks of weird weather and non-stop fire news around the start of January, there were detectable Weimar republic vibes. Strange currents moved between unlikely people. Friends who lead stable middle-class lives had uncharacteristic nights of chaos, and found themselves going home with strange men they’d met in bars, or on drug binges with kids they had mentored, or discussing with their friends whether they would or would not kill themselves if the climate catastrophe got too bad. I found myself deep in plans with strangers to join some agrarian farming collective they were starting in the Otways and accepting detailed advice about how to build a bunker on my property, which I was scared enough to actually contemplate because my fire plan involved escaping on a bicycle.

Meanwhile, all throughout this summer, the smoke moved around us, like a viral social media campaign, documented and populating the social media feeds of people first in Sydney, then Canberra and later Melbourne.

One day in mid-January I woke up in my cottage in central Victoria and there it was – a heavy taint in the air that had the previous day smelt so pure and clean, of oat grass dried in the wind.

That day it was hot and a friend and I went swimming in a reservoir out of town. The water was brackish and warm and all around was the bush, dry, silent and crackling in the 35-degree heat. As we rounded the bend (dense forest on either side, the tall gums bent and meeting like a cathedral roof) the scene was not one we interpreted as picturesque but through the lens of the Pyrocene. “Imagine all this on fire,” my friend said as we drove through it.

How much of this summer is not just imagining yourself in another’s place but is the collective collapse between imagination and reality? This summer we no longer have to imagine any more.

• Brigid Delaney is a Guardian Australia columnist