In most disaster movies there comes a singular moment where humanity launches a last-ditch attempt to save itself.

Sometimes it's a nuclear-equipped space shuttle sent to destroy an asteroid heading for Earth.

In others it's a fleet of World War Two-era planes, sent on a hopeless mission to fight the alien mothership.

Today, on 6 June (aka 'IPv6 Launch'), it's the internet's turn.

A crucial PR offensive to move to a new internet address system is being rolled out on Wednesday, ahead of what experts say could be the end for the web as we know it.

The issue is that the Internet was built with space for only a couple of billion addresses for businesses, users and ISPs.

In the mid-90s it was realised that this system - IPv4 - was not large enough to cope with the Internet's growth, and a much more effective version - IPv6 - was developed to replace it. But the switch still hasn't happened and now we've virtually run out of space.

If we do run out of addresses the internet would continue to run. But new customers would be signed up to IPv6 and would not be able to access many old websites. The result would be catastrophic for growth, says the IPv6 Act Now campaign.

'IPv6 Launch', which follows a one-day switchover test last year, is the moment that the internet decides to save itself, explains Axel Pawlik, MD of Ripe, the internet registry for Europe, Middle East and Central Asia.

Websites and ISPs including Google, Facebook, Time Warner Cable, Yahoo and Microsoft are officially making the switch on Wednesday, but now the IPv6 Act Now campaign says others must follow suit.

"We have very few months left," Pawlik told the Huffington Post. "Something needs to be done."

"The design question when the Internet was created was 'how many will we ever need?'" he explains. "Okay, it's a small network, academia, a bit of a sandbox, let's say a couple of million.' So they designed it to have 32 bits of address space."

"Then there was an agreement that the next generation protocol would be IPv6, with basically the same features only many more addresses."

"It's such a big number that people have difficulty finding the term for that number."

So... we just make the switch. Sounds simple, right?

Nope.

First, many internet service providers (ISPs) and some web services have been - and still are - reluctant to make the move to IPv6. That will include new hardware for consumers, who will eventually have to move to IPv6 themselves.

"They all had more important things to do next week, next month and next year, like get money from customers, and those customers never asked for IPv6... The pressure from the market wasn't there."

Now many ISPs are on board. But some businesses are yet to be convinced.

So if some are still dragging their feet, what is actually being launched on IPv6 Launch Day?

"Frankly," Pawlik says. "The PR."

Last year's IPv6 Day was intended to prove the new protocol wouldn't break the Internet, he says. And it worked.

"It went fairly well, a bit of a non-event - which is good news. But what we also saw is that after the nice experiment many people switched off IPv6 again. Why switch it off if it works? What we want this year is to convince people not to switch it off."

Now IPv6 Launch is intended to mark the official opening day of the new protocol.

"We want people to become aware and call their ISPs and say 'I want IPv6!"

"Then maybe that remaining ISP that was a bit late, actually does something about it before it's too late."

Unfortunately for now customers are still at the mercy of the ISPs.

Including Pawlik.

"At my home I am connected to a cable provider and for years they've said 'no we have no IPv6 plans," he said.

"I ask them once a year - they say 'don't worry'. I hate it when they say that... Now they've said yes, we know about it and we are planning. But I still don't have IPv6 at home yet."

"But I fully expect next time they send me a router, I will."