I have a grim message for you from the future. About three weeks into the future, to be precise.

My wife, our two daughters and I stepped off the plane in Los Angeles earlier this week as if emerging from a dream — or was it entering one? The reality we walked into seemed nothing like the one we had left in New York a few hours earlier.

In our home neighbourhood in Brooklyn, friends had become strangers, and strangers had become threats.

Our usual Sesame Street existence — in which a life of shared outdoor space turned every walk along the brownstones into a string of impromptu conversations with neighbours, crossing guards and shopkeepers — had descended into a lonely and menacing dash for essential supplies.

People would cross the street as they saw you approaching. Regulars at our local cafe, when it was still open, would shout at others in line to keep their distance; parents in the park would usher their kids away from you with surgical-gloved hands.

Everyone was a threat. Anyone could kill.

After a string of cancellations and last minute re-bookings, we finally made it onto one of the last flights out — a hasty emigration brought forward by circumstance, all of our belongings left behind indefinitely. The plane was empty.

When an airport worker at LAX started yelling at us to bunch closer together, two by two instead of single-file, I realised the coronavirus did not seem to represent the threat it did in Brooklyn.

Fifteen hours later, as we disembarked in Sydney, it did not seem to exist at all.

It's too late for New York, but not for Sydney

Like the background noise of an airplane safety demonstration, we were given vague instructions by quarantine officers to self-isolate for two weeks, handed a Department of Health fact sheet, then released into the wild.

We stepped outside to be transported back in time, to New York three weeks ago.

Schools and businesses were still open, beaches were packed (later that day Bondi closed and further shutdowns were announced), and people mingled — perhaps in denial of the new reality headed their way.

Ed Coper with his wife and daughters in New York, in happier times. ( Supplied )

There's a meme circulating the internet at the moment, that climate change wishes it had the same PR person as COVID-19.

But it's the similarities of the two crises we should be looking at, not the differences.

The main barrier to effective action on either is that we seem incapable of taking action until we see the problem manifest itself before our eyes, and the longer we leave it, the more drastic the intervention will be needed.

Sydney, you still have a chance to take the pandemic seriously — to take small but swift steps now and potentially avoid more significant disruption later.

For New York City, which is emerging as the epicentre of the virus's spread in the US, it is too late. The healthcare system is already beyond breaking point and cases are said to be doubling every three days.

It may not seem real to you until you know someone who is infected.

We know a dozen or more — young, healthy people now seriously ill. A parent at our local school. A friend's newborn baby. Hopalong Andy, our kids' singalong cowboy musician.

Prologue to a farce or a tragedy—or both

If New York could have the last three weeks back, it would. That innocuous play on the swings. That last trip on the subway to work. That last catchup at the pub before the "serious" lockdown started. All of these things now seem reckless in hindsight.

But you still have those three weeks ahead of you, Sydney.

You can still rethink that barbecue with your healthy-looking neighbour, that playdate in lieu of day care, that beer with your friend — after all, they would never get the virus, it's for cruise passengers and international arrivals.

A little bit of self-control, of erring on the side of caution, can still arrest the exponential tsunami that is already spreading through your city.

Ed Coper and his family are currently in 14-day isolation in Sydney. ( Supplied )

Back in Brooklyn, nobody looked sick in our community; we now know it has been circulating there for weeks and possibly longer — some who had the flu last month are now being told it was probably COVID-19.

One of America's founding fathers, James Madison, warned in 1822 that a "A popular Government, without popular information, or the means of acquiring it, is but a Prologue to a Farce or a Tragedy; or, perhaps both."

He was imploring the fact that an informed citizenry was necessary for democracy to thrive.

Australia's leaders are armed with all the information they need to avert disaster.

They see Italy (where 900 people died just on the day we landed in Sydney), they see America (where experts are warning of deaths likely in the millions).

Incremental piecemeal closures were the cause of Italy's historic catastrophe, they're saying.

Australians are now armed with information to prevent this prologue becoming a full-blown tragedy.

It is not just coming for your boomer parents who are still insisting on attending christenings in Bowral, it is coming for you.

For the doctors and nurses you will rely on to help you. For your cancer-surviving colleague; your diabetic friend. People you know will die.

Then you will look back and wonder why, in the face of all this information, did we not act like our lives depended on it.

Ed Coper is executive director of the New York-based Center for Impact Communications, and is currently a few days into two weeks of isolation in Sydney.